Model III ROM Explained - Part 2

Go put a comma or decimal point in the input buffer if necessary.

105E-105F

LD (HL),"0"

Save a 0 character at the location of the input buffer pointer in register pair HL.

1060-1062

CALL Z,09C9H

If there was no scaling, GOSUB to 09C9H to bump the value of the input buffer pointer in register pair HL if necessary.

1063-1065

Go convert the binary value in REG 1 to ASCII, the result being stored in the input buffer pointer.

1066

DEC HL

Backspace the last character by decrementing the value of the input buffer pointer in register pair HL.

1067

LD A,(HL)

Load register A with the value at the location of the input buffer pointer in register pair HL (which is the previous character).

1068-1069

CP 30H

Check to see if the value in register A is a 0 (which is 30H).

106A-106B

JR Z,1066H

Loop until the character at the location of the input buffer pointer in register pair HL is not a zero character.

106C-106D

CP "."

Check to see if the character at the location of the input buffer pointer in register A is a ..
NOTE: Results from a CP:

Z: A and * are the same
NZ: A and * are NOT the same
C: A < *
NC: A => *

106E-1070

CALL NZ,09C9H

If its NOT a decimal point, GOSUB to bump the value of the input buffer pointer in register pair HL.

1071

POP AF

Get the value from the stack (i.e., the exponent) and put it in register pair HL.

1072-10731

JR Z,1093H

If the exponent is zero, jump to 1093H.

1074

PUSH AF

Save the exponent (stored in AF) back to the stack.

1075

RST 20H

We need to check the value of the current number type flag, so we call the TEST DATA MODE routine at RST 20H.
NOTE: The RST 20H routine determines the type of the current value in REG 1 and returns a combination of STATUS flags and unique numeric values in the A Register according to the data mode flag (40AFH).

The results are returned as follows:

If the Variable Type is ...	and the Flags are set ...	... then Register A will be set ...
Integer	NZ/C/M/E	-1
String	Z/C/P/E	0
Single Precision	NZ/C/P/O	1
Double Precision	NZ/NC/P/E	5

1076-1077

LD A,22H

Load register A with the starting value for a D or E character.

1078

ADC A,A

Multiply the value of the character in register A by two and add in the value of the CARRY FLAG from the number type flag test. This will result with A it being a D if the value is SINGLE precision and an E if the value is DOUBLE precision.

1079

LD (HL),A

Save the exponent designation (the D or E in register A) at the location of the input buffer pointer in register pair HL.

107A

INC HL

Bump the value of the input buffer pointer in register pair HL, which is the first position of the exponent in the buffer.

107B

POP AF

Get the value of the exponent from the stack and put it in register A.

107C-107D

LD (HL),2BH

Save a + (=2BH) at the location of the input buffer pointer in register pair HL.

107E-1080

JP P,1085H

Skip the next 3 instructions (by jumping to 1085H) if the exponent is positive.

1081-1082

LD (HL),2DH

Save a - (which is 2DH) at the location of the input buffer pointer in register pair HL.

1083

CPL

Convert the negative exponent to positive by reversing the value of the exponent in register A and ...

1084

INC A

... bumping the value of the exponent in register A.

1085-1086

LD B,2FH

At this point, the exponent is positive. Next step is to load register B with a 0 minus one (which is a /).

1087

INC B

Bump the value of the ASCII character in register B (so now it is an 0). This is the start of a 3 Opcode routine to divide by 10 using compound subtraction.

1088-1089

SUB A,0AH

Subtract ten from the value of the exponent in register A.

108A-108B

JR NC,1087H

Loop until the value of the exponent in register A is less than ten. B holds the quotient (e.g., the number of times the subtraction had to occur to get to a remainder less than 10).

108C-108D

ADD A,3AH

Since A is holding the remainder of the 'divide-by-10' routine above, add 3AH to it so that it will be an ASCII digit.

108E

INC HL

Bump the value of the input buffer pointer in register pair HL.

108F

LD (HL),B

Save the ASCII character in register B (which is the first digit of the exponent in ASCII) at the location of the input buffer pointer in register pair HL.

1090

INC HL

Bump the value of the input buffer pointer in register pair HL.

1091

LD (HL),A

Save the value of the ASCII character in register A (which is the second digit of the exponent in ASCII) at the location of the input buffer pointer in register pair HL.

1092

INC HL

Bump the value of the input buffer pointer in register pair HL.

1093-1094

LD (HL),00H

Save an end of the ASCII string character (designated as 00H) at the location of the input buffer pointer in register pair HL.

1095

EX DE,HL

Load register pair DE with the ending address of the input buffer pointer.

1096-1098

LD HL,4130H

Load register pair HL with the starting address of the input buffer pointer.
NOTE: 4130H-4149H holds Internal print buffer.

1099

RET

Return.

109A

INC HL

Bump the value of the input buffer pointer in register pair HL.

109B

PUSH BC

Save the value in register pair BC to the stack (currently B has the number of #'s before the current vale of the input buffer pointer and C has the number of #'s after).

109C-109D

CP 04H

Check to see if the current number type in REG 1 is single or double precision. Results:

If A=04H it sets the ZERO FLAG
If A<04H then the CARRY FLAG will be set
If A>=04H then the NO CARRY FLAG will be set

109E

LD A,D

Load register A with the value of the edit flag in register D.

109F-10A1

JP NC,1109H

Jump to 1109H if the current value in REG 1 is either single precision or double precision (i.e., A>=04H since 4=Single precision and 8=Double precision

10A2

RRA

Rotate A right one bit to put the value of the exponential notation flag into the CARRY FLAG.

10A3-10A5

JP C,11A3H

JUMP to 11A3H if exponential notation is requested.
Alternative interpretation is Jump to 11A3H if the variable is a string; which will leave us now with only an integer value.

10A6 - This is where the PRINT USING routine will edit for INTEGER values.

10A6-10A8

LD BC,0603H

Load register pair BC with a default value of 0603H (so that Register B has the number of leading digits of 6 and Register C has the comma counter of 3).

10A9-10AB

CALL 1289H

Go check to see if commas are requested. If no comma is requested, set Register C to zero.

10AC

POP DE

Get the value from the stack and put it in register pair DE. This will put the number of #'s to the left of the decimal point into D.

10AD

LD A,D

Load register A with the number of digits requested to the left of the decimal point in register D.

10AE-10AF

SUB A,05H

Since the maximim number of digits allowed for an integer to the left of the decimal point is 5, subtract 5 from the number of digits to the left of the decimal point requested.

10B0-10B2

Go put leading zeros into the input buffer if the number of digits to the left of the decimal point requested is greater than the number of digits to the left of the decimal point for the maximum length of an integer value (meaning, the POSITIVE flag has been set).

10B3-10B5

CALL 132FH

Call the INTEGER TO ASCII routine at 1232F (which converts the integer in REG 1 to ASCII and stores the ASCII string in the buffer pointed to in HL).

10B6

LD A,E

Load register A with the number of digits to the right of the decimal point requested (which is stored in register E).

10B7

OR A

Check to see if there are any digits to the right of the decimal point requested and set the status flags accordingly.

10B8-10BA

CALL Z,092FH

Go decrement the value of the input buffer pointer in register pair HL if there are no digits to the right of the decimal point requested.

10BB

DEC A

Decrement the number of digits to the right of the decimal point in register A. This tests to see if no count was given.

10BC-10BE

If the POSITIVE flag is set, gosub to 1269H to add trailing zeros to the ASCII string if necessary.

10BF

PUSH HL

Save the current input buffer pointer (stored in register pair HL) to the stack.

10C0-10C2

CALL 0FF5H

Go edit the ASCII string in the input buffer.

10C3

POP HL

Get the saved input buffer pointer value from the stack and put it in register pair HL.

10C4-10C5

JR Z,10C8H

Jump to 10C8H if the sign follows the ASCII string.

10C6

LD (HL),B

So now we know a sign does not follow the value so we save the character in register B (which should be a space) at the location of the input buffer pointer in register pair HL.

10C7

INC HL

Bump the value of the input buffer pointer in register pair HL

10C8-10C9

LD (HL),00H

Terminate the buffer by saving an end of the ASCII string character (=00H) at the location of the input buffer pointer in register pair HL.

10CA-10CC

LD HL,412FH

Load register pair HL with the starting address of the input buffer pointer (which is 412FH) minus 1 (because the first instruction of the following common code is add 1 to HL).

10CD

INC HL

Bump the value of the input buffer pointer in register pair HL.

10CE-10D0

LD A,(40F3H)

Load register A with the LSB of the address of the decimal point for the ASCII string.
NOTE: 40F3H-40F4H holds the temporary storage location.

10D1

SUB A,L

Subtract the LSB of the input buffer pointer address in register L from the value in register A.

10D2

SUB A,D

Subtract the number of digits to the left of the decimal point in register D from the adjusted value in register A.

10D3

RET Z

Return if the input buffer pointer in register pair HL points to the start of the ASCII string.

10D4

LD A,(HL)

So now we know we are not at the start of the field, so we fetch the character at the location of the input buffer pointer in register pair HL into Register A.

10D5-10D6

CP 20H

Check to see if the character at the location of the input buffer pointer in register A is a space (which is a blank).

10D7-10D8

JR Z,10CDH

Jump back to 10CDH if the character at the location of the input buffer pointer in register pair HL is a space so that we keep looking until we are either at the start of the field, or a "+", "-", or "$" is found.

10D9-10DA

CP "*"

Check to see if the character at the location of the input buffer pointer in register A is a *.

10DD

DEC HL

Since we want to ignore "*"'s decrement the value of the input buffer pointer in register pair HL so it will get re-tested.

10DE

PUSH HL

Save the value of the input buffer pointer in register pair HL to the stack.

10DF

PUSH AF

Save the value in register pair AF (which is the current character) to the stack.

10E0-10E2

LD BC,10DFH

Load register pair BC with the return address for use in case we have a -, a +, or a $.

10E3

PUSH BC

Save the return address in register pair BC to the stack.

10E4

RST 10H

Since we need to bump the current input buffer pointer in register pair HL until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

10E5-10E6

CP "-"

Check to see if the character at the location of the input buffer pointer in register A is a -.

10E7

RET Z

Return (to 10DFH) if the character at the location of the input buffer pointer in register A is a -.

10E8-10E9

CP "+"

Check to see if the character at the location of the input buffer pointer in register A is a +.

10EA

RET Z

Return (to 10DFH) if the character at the location of the input buffer pointer in register A is a +.

10EB-10EC

CP "$"

Check to see if the character at the location of the input buffer pointer in register A is a $.

10ED

RET Z

Return (to 10DFH) if the character at the location of the input buffer pointer in register A is a $.

10EE

POP BC

We don't need a shortcut to jump to 10DFH anymore, so let's get the real return address from the stack and put it in register pair BC.

10EF-10F0

CP "0"

Check to see if the character at the location of the input buffer pointer in register A is a 0.

10F1-10F2

JR NZ,1102H

Jump to 1102H if the character at the location of the input buffer pointer in register A isn't a 0.

10F3

INC HL

Bump the value of the input buffer pointer in register pair HL so that we skip to the next character.

10F4

RST 10H

Since we need to bump the current input buffer pointer in register pair HL until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

10F5-10F6

JR NC,1102H

Jump to 1102H if the character at the location of the input buffer pointer in register A isn't a numeric character.

10F7

DEC HL

Decrement the value of the input buffer pointer in register pair HL to backspace to the last character examined.

10F8

01 2B 77

Z-80 Trick! The byte at this memory location, 01H, is there to turn the real instruction that follows in 10F9H into a harmless LD BC,xxxx. This way, if you are processing straight down in order, it skips the next command at 10F9H (in this case a DEC HL) because it wasn't a command, it was a hex number to be loaded into BC! Instead, if you jump to 10F9H, you skip this byte and it is an DEC HL.

10F9

DEC HL

Decrement the value of the input buffer pointer in register pair HL (we needed that Z-80 trick to avoid a double backspace in passing through).

10FA

LD (HL),A

Save the character in register A at the location of the input buffer pointer in register pair HL.

10FB

POP AF

Get the value from the stack and put it in register pair AF.

10FC-10FD

JR Z,10F9H

Loop until the end of the field is reached (by finding a 00H).

10FE

POP BC

Clear the stack.

10FF-1101

JP 10CEH

Jump back to 10CEH to restart the scan.

1102

POP AF

Restore the character at the start of the field from the stack and put it in register pair AF.

1103-1104

JR Z,1102H

Loop until the beginning of the field is found.

1105

POP HL

Get the starting address of the field from the stack and put it in register pair HL.

1106-1107

LD (HL),25H

Save a % character at the location of the input buffer pointer in register pair HL (which is the starting address).

1108

RET

Return.

1109 - This is where the PRINT USING routine will edit for FLOATING POINT values.

1109

PUSH HL

Save the current input buffer pointer in register pair HL to the stack.

110A

RRA

Rotate A right one bit, with Bit 0 going to the CARRY FLAG. This will allow us to test bit 0 of the edit flags to see if exponential notation is requested by the edit flag in register A.

110B-110D

JP C,11AAH

Jump to 11AAH if exponential notation is requested by the edit flag in register A on a floating point number.

110E-110F

JR Z,1124H

Jump to 1124H if the current value in REG 1 is single precision.

1110-1112

LD DE,1384H

Load register pair DE with the address of the DOUBLE PRECISION value to be compared to the current value in REG 1. Register pair DE points to a double precision constant equal to 1el6.

1113-1115

CALL 0A49H

Go compare the double precision constant pointed to by register pair DE (which is 1el6) to the double precision value in REG 1.

1116-1117

LD D,10H

Load register D with the maximum length of a double precision value (which is 16).

1118-111A

JP M,1132H

Jump to 1132H if the double precision value in REG 1 is less than or equal to 1el6.

111B

POP HL

So now we know the double precision value in REG 1 exceeds 1x10^16. Get the current input buffer pointer from the stack and put it in register pair HL.

111C

POP BC

Get the value from the stack and put it in register pair BC, resulting in B containing the number of #'s before and C containing the number of #'s after.

111D-111F

CALL 0FBDH

Go convert the double precision value in REG 1 to an ASCII string. The goal is to reenter the edit routine until the double precision value is less than 1x10^16.

1120

DEC HL

Decrement the input buffer pointer in register pair HL to get it back to the current position.

1121-1122

LD (HL),"%"

Save a % character at the location of the input buffer pointer in register pair HL.

1123

RET

Return.

1124H - Continuation point if the current value in REG 1 is single precision.

1124-1126

LD BC,B60EH

Load register pair BC with the exponent and the MSB of a single precision constant.

1127-1129

LD DE,1BCAH

Load register pair DE with the NMSB and the LSB of a single precision constant. Register pairs BC and DE now hold a single precision constant equal to 1x10^16.

112A-112C

Call the SINGLE PRECISION COMPARISON routine at 0A0CH.

NOTE: The routine at 0A0CH algebraically compares the single precision value in BC/DE to the single precision value REG 1.
The results are stored in A as follows:

A=00H if REG 1 = BCDE
A=01H if REG 1>BCDE; and
A=FFH if REG 1<BCDE.

112D-112F

JP P,111BH

Jump back to 111BH if the the POSITIVE flag is set (meaning the single precision value in REG 1 is greater than 1x10^16).

1130-1131

LD D,06H

Now we know that the SINGLE precision value in REG 1 is less than 1x10^16. Load register D with the maximum length of a single precision value (which is 6).

1132-1134

Go check the sign of the value in REG 1.

1135-1137

CALL NZ,1201H

GOSUB to 1201H to adjust the current value of REG 1 so that the single precision value is 99,999 < X < 999,999. On the return from that GOSUB, A will equal the number of times the value was scaled up or down as a + or -.

1138

POP HL

Get the origin of the ASCII buffer from the stack and put it in register pair HL.

1139

POP BC

Get the value from the stack and put it in register pair BC, resulting in B containing the number of #'s before and C containing the number of #'s after.

113A-113C

JP M,1157H

JUMP forward to 1157H if the value in REG 1 had to be scaled up (multiplied by 10) to get it in range.

113D

PUSH BC

Save the value in register pair BC (B was the number of #'s before and C is the number of #'s after) to the stack.

113E

LD E,A

Load register E with the number of times the current value in REG 1 was divided.

113F

LD A,B

Load register A with the number of digits before the decimal point requested.

1140

SUB A,D

Subtract the maximum length for the current number type in register D (which is 6) from the number of digits requested in register A.

1141

SUB A,E

Subtract the number of times the current value in REG 1 was divided in register E from the adjusted value in register A.

1142-1144

If the POSITIVE flag is set, gosub to 1269H to put leading zeros into the input buffer if necessary.

1145-1147

CALL 127DH

GOSUB to 127DH to figure the comma count and the position of the decimal point.

1148-114A

GOSUB to 12A4H to convert the integer portion of the current value in REG 1 to an ASCII string.

114B

OR E

Check to see if there are any trailing zeros needed by testing the number of times the value was scaled.

114C-114E

CALL NZ,1277H

Go put trailing zeros into the input buffer if necessary.

114F

OR E

Check to see if commas or the decimal point is needed.

1150-1152

CALL NZ,1291H

Go put commas and the decimal point into the input buffer if necessary.

1153

POP DE

Get the edit counts value from the stack and put it in register pair DE.

1154-1156

JP 10B6H

Jump to 10B6H to convert the fractional portion fo the number to ASCII.

1157 - LEVEL II BASIC MATH ROUTINE - "FFXXVS"

This routine will print a SINGLE PRECISION or DOUBLE PREVISION number that has fractional digits

1157

LD E,A

Load register E with the number of times the current value in REG 1 was scaled (multiplied by 10).

1158

LD A,C

Load register A with the number of digits requested to the right of the decimal point.

1159

OR A

Check to see if any digits to the right of the decimal point was requested.

115A-115C

CALL NZ,0F16H

Go decrement the number of digits requested to the right of the decimal point if necessary.

115D

ADD A,E

Add the number of times the current value was multiplied in register E to the number of digits to the right of the decimal point requested in register A.

115E-1160

JP M,1162H

Jump if the value in REG 1 must be scaled down.

1161

XOR A

Zero register A and indicate that there is on scaling down needed.

1162

PUSH BC

Save the value in register pair BC (B was the number of #'s before and C is the number of #'s after) to the stack.

1163

PUSH AF

Save the value in register pair AF (the scale count) to the stack.

1164-1166

CALL M,0F18H

GOSUB to 0F18H to divide the value in REG 1 by ten, A times, if necessary.

1167-1169

JP M,1164H

Loop until the value in REG 1 is properly adjusted. When this is done, A will hold the number of times it was divided by 10.

116A

POP BC

Get the original scale count from the stack and put it in register pair BC.

116B

LD A,E

Load register A with the number of times the value in REG 1 was multiplied in register E.

116C

SUB A,B

Subtract the value in register B from the value in register A.

116D

POP BC

Get the before/after value from the stack and put it in register pair BC.

116E

LD E,A

Load register E with the adjusted scale factor value in register A.

116F

ADD A,D

Add the length of the maximum size for the current value in register D to the adjusted scale factor value in register A. This will set the sign flag.

1170

LD A,B

Load register A with the number of #'s before (stored in B).

1171-1173

JP M,117FH

Jump to 117FH if there are no digits to the left of the decimal point.

1174

SUB A,D

We now know there are leading digits so, subtract the maximum length for the current value in register D (6 for SINGLE precision and 10 for DOUBLE precision) from the adjusted value in register A.

1175

SUB A,E

Then, subtract the adjusted scale value in register E from the adjusted value in register A.

1176-1178

If that subtraction leads to a positive number, go put leading zeros into the input buffer.

1179

PUSH BC

Save the value in register pair BC (B was the number of #'s before and C is the number of #'s after) to the stack.

117A-117C

CALL 127DH

GOSUB to set up BC for decimal point and comma counters.

117D-117E

JR 1190H

Jump to 1190H to edit the numbers before the decimal point.

117F - LEVEL II BASIC MATH ROUTINE - "FFXXV3"

This routine will print a number without integer digits.

117F-1181

CALL 1269H

Go put leading zeros into the input buffer if necessary.

1182

LD A,C

Load Register A with the number of bytes requested to the right of the decimal point (in register C) because C is about to get wiped.

1183-1185

CALL 1294H

GOSUB to 1294H to put a decimal point into the input buffer.

1186

LD C,A

Reload register C with the number of digits requested to the right of the decimal point in register A.

1187

XOR A

Zero Register A.

1188

SUB A,D

Subtract the maximum length for the current value in register D from the value in register A.

1189

SUB A,E

Subtract the value in register E from the adjusted value in register A.

118A-118C

CALL 1269H

GOSUB to 1269H to put that many zeroes into the input buffer (if necessary).

118D

PUSH BC

Save the value in register pair BC (B was the number of #'s before and C is the number of #'s after) to the stack.

118E

LD B,A

Load register B with the value in register A (which is 0).

118F

LD C,A

Load register C with the value in register A (which is 0).

119A - LEVEL II BASIC MATH ROUTINE - "FFXXV7"

This routine will print trailing zeroes.

1190-1192

GOSUB to 12A4H to convert the integer portion of the SINGLE precision value in REG 1 to an ASCII string.

1193

POP BC

Get the number of #'s before and number of #'s after and put it back in register pair BC.

1194

OR C

Check to see if there are any digits to the right of the decimal point requested and set the status accordingly.

1195-1196

JR NZ,119AH

Jump to 119AH if there are digits to the right of the decimal point requested.

1197-1199

LD HL,(40F3H)

Now we know that there are no digits to the right of the decimal point. Load register pair HL with the position of the decimal point (which is stored in 40F3H).
NOTE: 40F3H-40F4H holds the temporary storage location.

119A

ADD A,E

Add the value in register E to the value in register A to get the number of digits before the decimal point.

119B

DEC A

Decrement the adjusted value in register A.

119C-119E

If dropping A by 1 still results in a positive number, GOSUB 1269H to put that number of zeros into the input buffer.

119F

LD D,B

Load register D with the number of digits to the left of the decimal point requested (from Register B).

11A0-11A2

JP 10BFH

Jump to 10BFH to edit the ASCII value.

11A3 - LEVEL II BASIC MATH ROUTINE - "FFXIFL"

This routine will print an integer in fixed format/floating point notation.

11A3

PUSH HL

Save the current position of the input buffer (in register pair HL) to the stack.

11A4

PUSH DE

Save the edit flags (in register pair BC) to the stack.

11A5-11A7

CALL 0ACCH

GOSUB 0ACCH to convert the integer value in REG 1 to a SINGLE precision value.

11A8

POP DE

Get the edit flags from the stack and put it in register pair DE.

11A9

XOR A

Zero register A, clear the status flags.

11AA - LEVEL II BASIC MATH ROUTINE - "FFXFLV"

This routine will print a SINGLE or DOUBLE PRECISION number in fixed format/floating point notation.

11AA-11AC

JP Z,11B0H

Slip the next 2 instructions to 11B0H (using a Z-80 trick) to skip the next instruction if the current value in REG 1 is SINGLE precision.

11AD-11AE

LD E,10H

Load register E with the maximum length of a double precision value (which is 16).

11AFH

01 + LD E,06H
or
LD BC, 1E06H

Z-80 Trick! By putting a 01 here, the opcode becomes a 3 byte opcode, turning 01 1E 06 into LD BC, 1E06H. This would corrupt BC, but otherwise would then make the next instruction 11B2H, skipping the next instruction of LD E,06H because, well, it doesn't exist!

11B0H - Continuation Routine (From 11AAH) if the current value in REG 1 is SINGLE precision.

11B0-11B1

LD E,06H

Load register E with the maximum length of a single precision value (which is 6).

11B2-11B4

GOSUB 0955H to check the sign for the current value in REG 1.

11B5

SCF

Set the CARRY FLAG (to force a jump at 11F3 on the first pass).

11B6-11B8

CALL NZ,1201H

GOSUB to 1201H to scale the current value in REG 1 if its nonzero.

11B9

POP HL

Get the input buffer position from the stack and put it in register pair HL.

11BA

POP BC

Get the number of #'s before and the number of #'s after from the stack and put it in register pair BC.

11BB

PUSH AF

Save the decimal point and the flag for test at 11F3H in register pair AF to the stack.

11BC

LD A,C

Load register A with the number of digits to the right of the decimal point requested (stored in register C).

11BD

OR A

Set the status so we can see if there are any digits to the right of the decimal point requested through a zero register.

11BE

PUSH AF

Save the original trailing digit count (in register pair AF) to the stack.

11BF-11C1

CALL NZ,0F16H

If the trail count is not zero, then GOSUB to 0F16H to decrement the number of digits requested to the right of the decimal point in register A.

11C2

ADD A,B

Add the number of digits requested for the left of the decimal point in register B to the number of digits requested to the right of the decimal point in register A.

11C3

LD C,A

Load register C with the total digit count (held in register A).

11C4

LD A,D

Load register A with the value of the edit flag in register D.

11C5-11C6

AND 04H

Check to see if the sign follows the ASCII string.

11C7-11C8

CP 01H

Set the CARRY FLAG according to the sign following the ASCII string test (it will be No Carry if a sign follows).

11C9

SBC A,A

Adjust register A so that it will reflect the sign following the ASCII string test (A will be 0 if there is no sign, and FEH otherwise).

11CA

LD D,A

Load register D with the edit flag (from register A).

11CB

ADD A,C

Add the value in register C to the value in register A so as to adjust the count of the digits to print if a sign follows.

11CC

LD C,A

Load register C with the adjusted value in register A.

11CD

SUB A,E

Subtract the value in register E from the adjusted value in register A so that A will now contain the number of times to divide by 10.

11CE

PUSH AF

Save the divisor count (from register pair AF) to the stack.

11CF

PUSH BC

Save the character count (from register pair BC) to the stack.

11D0-11D2

CALL M,0F18H

GOSUB to 0F18H to divide the current value in REG 1 by ten, Register A number of times.

11D3-11D5

JP M,11D0H

Loop back 1 instruction (divide by 10) until the division has been completed.

11D6

POP BC

Get the counter of the #'s from the stack and put it in register pair BC.

11D7

POP AF

Get the division count from the stack and put it in register pair AF.

11D8

PUSH BC

Save the value in Register Pair BC to the STACK.

11D9

PUSH AF

Save the value in register pair AF to the stack.

11DA-11DC

JP M,11DEH

Skip the next instruction (i.e., jump to 11DEH) if there are any trailing zeroes.

11DD

XOR A

Zero register A and all status flags.

11DE

CPL

Make the trailing zero count posivite by inverting the value in register A.

11DF

INC A

Bump the value in register A so that it will be positive.

11E0

ADD A,B

Add the number of digits requested to the left of the decimal point in register B to the adjusted value in register A.

11E1

INC A

Bump the adjusted value in register A.

11E2

ADD A,D

Add the value of the maximum length for the current number type in register D (6 for single precision, 16 fo double precision) to the adjusted value in register A.

11E3

LD B,A

Copy Register A into Register B so that B holds the number of digits before the decimal point.

11E4-11E5

LD C,00H

Load register C with zero (so that there are no commas).

11E6-11E8

GOSUB to 12A4H to convert the current value in REG 1 to an ASCII string.

11E9

POP AF

Get the number of #'s before from the stack and put it in register pair AF.

11EA-11EC

CALL P,1271H

GOSUB 1271H to put zeros into the trailing input buffer.

11ED

POP BC

Get the number of #'s before and the number of #'s after from the stack and put it in register pair BC.

11EE

POP AF

Get the count of numbers before the decimal point from the stack and put it in register pair AF.

11EF-11F1

CALL Z,092FH

GOSUB to 092FH to decrement the input buffer pointer in register pair HL if there are none.

11F2

POP AF

Get the first time flag from the stack and put it in register pair AF.

11F3-11F4

JR C,11F8H

Jump to 11F8H (to add the exponent) if the CARRY FLAG was set during the first pass.

11F5

ADD A,E

Add the value in register E to the value in register A.

11F6

SUB A,B

Subtract the number of digits to the left of the decimal point requested in register B from the adjusted value in register A.

11F7

SUB A,D

Subtract the value in register D from the value in register A to get the size of the exponent.

11F8

PUSH BC

Save the value in Register Pair BC to the STACK.

11F9-11FB

CALL 1074H

GOSUB to 1074H to figure the value of the exponent for the current value in REG 1

11FC

EX DE,HL

Load register pair HL with the value of the input buffer pointer in register pair DE.

11FD

POP DE

Get the value from the stack and put it in register pair DE. Clear the stack.

11FE-1200

JP 10BFH

Jump to 10BFH to edit the ASCII value.

1201 - Test the magnitude of SP and DP numbers, and clear the times the value was scaled - "FOUTNV"

This routine will scale (normalize) the number in the accumulator so that all the digits are in the integer part (i.e., between 99,999 and 999,999). The signed base 10 exponent is returned in Register A. Registers D and E are unchanged.

1201

PUSH DE

Save the value in register pair DE to the stack.

1202

XOR A

Zero register A and all the flags.

1203

PUSH AF

Save the value in register pair AF to the stack.

1204

RST 20H

If the Variable Type is ...	and the Flags are set ...	... then Register A will be set ...
Integer	NZ/C/M/E	-1
String	Z/C/P/E	0
Single Precision	NZ/C/P/O	1
Double Precision	NZ/NC/P/E	5

1205-1207

JP PO,1222H

If that test shows we have a SINGLE PRECISION number (through getting a Parity-Odd flag), jump to 1222H.

1208-120A

LD A,(4124H)

At this point we know we have a DOUBLE precision value. Load register A with the value of the exponent for the double precision value in REG 1.

120B-120C

CP 91H

Check to see if the double precision value in REG 1 uses more than 16 bits of precision for the integer portion of the double precision value.
NOTE: Results from a CP:

Z: A and * are the same
NZ: A and * are NOT the same
C: A < *
NC: A => *

120D-120F

JP NC,1222H

Jump to 1222H if the double precision value in REG 1 uses more than 16 bits of precision for its integer portion.

1210-1212

LD DE,1364H

Load register pair DE with the starting address for the double precision constant equal to 5.5x10e2.

1213-1215

LD HL,4127H

Load register pair HL with the starting address for REG2.
NOTE: 4127H-412EH holds REG 2.

1216-1218

CALL 09D3H

GOSUB to 09D3H to move the double precision constant of 5.5x10e2 into REG2.

1219-121B

CALL 0DA1H

GOSUB to 0DA1H to call the DOUBLE PRECISION MULTIPLY routine at 0DA1H (which multiplies the double precision value in REG 1 by the value in REG 2. The product is left in REG 1).

121C

POP AF

Get the number of times the DOUBLE precision value was multiplied to scale it up from the stack and put it in register pair AF.

121D-121E

SUB A,0AH

Subtract ten from the value in register A.

121F

PUSH AF

Save the value in register pair AF to the stack.

1220-1221

JR 1208H

Jump to 1208H so as to loop until the integer portion exceeds 2e16.

1222-1224

CALL 124FH

GOSUB to 124FH to compare the current value in REG 1 to 999999.5.

1225

RST 20H

If the Variable Type is ...	and the Flags are set ...	... then Register A will be set ...
Integer	NZ/C/M/E	-1
String	Z/C/P/E	0
Single Precision	NZ/C/P/O	1
Double Precision	NZ/NC/P/E	5

1226-1228

JR NC,1233H

In ROM 1.2 this is a big bug fix. Now if the shows we do NOT have a STRING, jump to 1233H

1229-122B

LD BC,9143H

Load register pair BC with the exponent and the MSB of a single precision constant.

122C-122E

LD DE,4FF9H

Load register pair DE with the NMSB and the LSB of a single precision constant. Register pairs BC and DE are now equal to a single precision constant of 99,999.945.

122F-1231

GOSUB to 0A0CH to call the SINGLE PRECISION COMPARISON routine at 0A0CH.

NOTE: The routine at 0A0CH algebraically compares the single precision value in BC/DE to the single precision value REG 1.
The results are stored in A as follows:

A=00H if REG 1 = BCDE
A=01H if REG 1>BCDE; and
A=FFH if REG 1<BCDE.

1232-1233

JR 123AH

Jump down two instructions to 123AH to test the results of the comparison.

1233-1235

LD DE,136CH

Load register pair DE with the starting address of a double precision constant equal to 9.9921El4.

1236-1238

CALL 0A49H

Go compare the double precision constant pointed to by register pair DE to the double precision value in REG 1.

1239-123B

JP P,124CH

Jump to 124CH if the current value in REG 1 is greater than the constant compared to it (more than 5 digits in integer or less than 17 digits in DOUBLE precision).

123C

POP AF

Get the value of the scaled counter from the stack and put it in register pair AF.

123D-123F

CALL 0F0BH

GOSUB to 0F0BH to multiply the current value in REG 1 by ten.

1240

PUSH AF

Save the value in register pair AF to the stack. A is the negative of the number of times the value was multiplied.

1241-1242

JR 1225H

Jump to 1225H to loop until it is between 999,999 and 99,999.

1243

POP AF

Get the scaled count from the stack and put it in Register A.

1244-1246

CALL 0F18H

GOSUB to 0F18H to divide the current value in REG 1 by ten.

1247

PUSH AF

Save the value in register pair AF to the stack. A is the count of the number of times it was divided.

1248-124A

CALL 124FH

GOSUB to 124FH to loop until the value in REG 1 is < 999,999.

124B

POP AF

Get the value from the stack and put it in register pair AF. A = + times divided or - times multiplied.
Difference between M1 and M3 ROMs: This change first appeared in the "new" ROMs for the Model I. The order of two instructions (OR A and POP DE) have been reversed for no apparent reason.

124C

POP DE

Get the value from the stack and put it in register pair DE.

124D

OR A

In ROM v1.2 sets the status flags. This also realigns the memory addresses from changes to v1.2 ROM.

124E

RET

Return.

124F

RST 20H

If the Variable Type is ...	and the Flags are set ...	... then Register A will be set ...
Integer	NZ/C/M/E	-1
String	Z/C/P/E	0
Single Precision	NZ/C/P/O	1
Double Precision	NZ/NC/P/E	5

1250-1252

JP PE,125EH

If that test shows we have a DOUBLE PRECISION number, jump to 125EH.

1253-1255

LD BC,9474H

Now that we know we have a single precision number, load register pair BC with the exponent and the MSB of a single precision constant.

1256-1258

LD DE,23F8H

Load register pair DE with the NMSB and the LSB of a single precision constant. Register pairs BC and DE are now equal to a single precision constant of 999,999.5.

1259-125B

A=00H if REG 1 = BCDE
A=01H if REG 1>BCDE; and
A=FFH if REG 1<BCDE.

125C-125D

JR 1264H

Jump to 1264H to test the result of the comparison.

125E-1260

LD DE,1374H

Load register pair DE with the starting address of a double precision constant equal to 1El6H.

1261-1263

CALL 0A49H

GOSUB to 0A49H to compare the double precision constant pointed to by register pair DE to the double precision value in REG 1.

1264

POP HL

Get the return address from the stack and put it in register pair HL so we can go to 1244H.

1265-1267

JP P,1243H

In ROM v1.2 the ROM addresses had moved 1 byte.

1268

JP (HL)

Jump to the caller (which was POPed from the stack).

1269H - This routine puts leading zeroes into the input buffer

1269

OR A

Check to see if the value in register A is equal to zero.

126A

RET Z

Return if the value in register A is equal to zero.

126B

DEC A

Decrement the value in register A to show that an ASCII zero was moved to the print buffer.

126C-126D

LD (HL),"0"

Save a 0 at the location of the input buffer pointer in register pair HL.

126E

INC HL

Bump the input buffer pointer in register pair HL.

126F-1270

JR 126AH

Jump back to 126AH until the number in Register A of ASCII zeroes were moved.

1271-1272

JR NZ,1277H

Jump to 1277H if not done adding trailing zeroes.

1273

RET Z

Return if done adding trailing zeroes.

1274-1276

GOSUB to 1291H to put decimal point and commas into the input buffer.

1277-1278

LD (HL),"0"

Save a zero character at the location of the input buffer pointer in register pair HL.

1279

INC HL

Bump the input buffer pointer in register pair HL.

127A

DEC A

Decrement the counter of trailing zeroes to add in register A.

127B-127C

JR 1273H

Jump back up to 1273H to RET.

127DH - Subroutine to set up BC for decimal point and comma counters. On entry: Register D holds the number of digits to print, Register E holds the count of the times the value was scaled up or down.

127D

LD A,E

Load register A with the value in register E so that A holds the count of the times the value was scaled up or down.

127E

ADD A,D

Add the number of digits to print (from Register D) to the value in register A.

127F

INC A

Bump the adjusted value in register A so now A holds the number of digits before the decimal point.

1280

LD B,A

Load register B with the leading digit count (from register A).

1281

INC A

Bump the value in register A so not A holds the leading digits + 2.

1282-1283

SUB A,03H

Subtract three from the adjusted value in register A which, when combined with the next instruction as a loop, divides modulo 3.

1284-1285

JR NC,1282H

Loop back 1 instruction until the value in register A is -1, -2, or -3.

1286-1287

ADD A,05H

Add 5 to A to get a positive remainder. This will give 4, 3, or 2 as the comma count.

1288

LD C,A

Load register C with the comma count in register A.

1289-128B

LD A,(40D8H)

Load register A with the value of the edit flag (stored at 40D8H).
NOTE: 40D8H-40D9H holds the temporary storage location.

128C-128D

AND 40H

Mask the EDIT FLAG against 40H (Binary: 0100 0000) to isolate bit 6 (the comma bit) in the edit flag word to see if commas are requested.

128E

RET NZ

Return with Register C = Comma count if commas are requested.

128F

LD C,A

Zero the comma counter in register C.

1290

RET

Return.

1291H - Subroutine to count the leading digits before the decimal point.

1291

DEC B

Decrement the decimal point counter in register B to see if the zero flag sets or not.

1292-1293

JR NZ,129CH

Jump to 129CH if the decimal point position hasn't been reached.

1294-1295

LD (HL),"."

Save a . at the location of the input buffer pointer in register pair HL.

1296-1298

LD (40F3H),HL

Save the address of the decimal point position (which is held in 40F3H) in register pair HL.
NOTE: 40F3H-40F4H holds the temporary storage location.

1299

INC HL

Bump the input buffer pointer in register pair H to the first character of the fractional part of a numberL.

129A

LD C,B

Zero the comma/decimal counter in register C (because B is zero since the above jump didn't fire) to stop any more decimal points and commas.

129B

RET

Return.

129CH - Continuation Routine (from 1292H) if the decimal point position hasn't been reached.

129C

DEC C

Decrement the decimal/comma counter in register C.

129D

RET NZ

Return if this location is not the end of a 3 character group (and so it doesn't need a comma).

129E-129F

LD (HL),","

If didn't jump out, then we need a comma here so put a comma at the location of the input buffer pointer in register pair HL.

12A0

INC HL

Bump the input buffer pointer (to account for the new comma) in register pair HL.

12A1-12A2

LD C,03H

Reset the comma counter by setting it to 3.

12A3

RET

Return.

12A4 - Routine to Convert the INTEGER porton of a DOUBLE precision value to its ASCII equivalent.

12A4

PUSH DE

Save the edit flags (stored in register pair DE) to the stack.

12A5

RST 20H

If the Variable Type is ...	and the Flags are set ...	... then Register A will be set ...
Integer	NZ/C/M/E	-1
String	Z/C/P/E	0
Single Precision	NZ/C/P/O	1
Double Precision	NZ/NC/P/E	5

12A6-12A8

JP PO,12EAH

If we have a single precision number (PO Flag Set), JUMP to 12EAH to convert a SINGLE precision number into its INTEGER equivalent.

12A9

PUSH BC

Now that we know we have a DOUBLE PRECISION number, save leading digit count/comma count (in register pair BC) to the stack.

12AA

PUSH HL

Save the input buffer address (in register pair HL) to the stack.

12AB-12AD

CALL 09FCH

GOSUB to 09FCH to mmove the double precision value in REG 1 to REG2.

12AE-12B0

LD HL,137CH

Load register pair HL with the starting address of a double precision constant equal to 0.5.

12B1-12B3

CALL 09F7H

GOSUB to 09F7H to move the double precision value pointed to by register pair HL to REG 1.

12B4-12B6

CALL 0C77H

GOSUB to 0C77H - DOUBLE PRECISION ADD function (which adds the double precision value in REG 2 to the value in REG 1 (which is the constant 0.5). Result is left in REG 1).

12B7

XOR A

Zero register A and clear the status flags.

12B8-12BA

CALL 0B7BH

GOSUB to 0B7BH to adjust the double precision result in REG 1.

12BB

POP HL

Get the input buffer address from the stack and put it in register pair HL.

12BC

POP BC

Get the counters from the stack and put it in register pair BC.

12BD-12BF

LD DE,138CH

Load register pair DE with the starting address of a series of double precision constants (i.e., a table of powers of 10 from 1.0x10E15 - 1.0x10E6) for the binary to ASCII conversion.

12C0-12C1

LD A,0AH

Load register A with the number of times to divide the double precision value in REG 1 by a power of 10.

12C2-12C4

GOSUB to 1291H to add a decimal point or comma (as applicable) into the input buffer if necessary.

12C5

PUSH BC

Save the count of digits before the decimal point and the count of digts after the decimal point (stored in register pair BC) to the stack.

12C6

PUSH AF

Save the division count (stored in register pair AF) to the stack.

12C7

PUSH HL

Save the current input buffer address (stored in register pair HL) to the stack.

12C8

PUSH DE

Save the address of the power table (stored in register pair DE) to the stack.

12C9-12CA

LD B,2FH

Load register B (which will be the quotient in ASCII for each division) with the ASCII value for a zero character minus one.

12CB

INC B

Bump the ASCII value for the digit in register B so as to start with ASCII "0".

12CC

POP HL

Get the address of the power table (i.e., the divisor) from the stack and put it in register pair HL and ...

12CD

PUSH HL

... put it right back into the stack so that it can be restored during the loop.

12CE-12D0

CALL 0D48H

GOSUB to 0D48H to subtract the double precision value pointed to by register pair HL from the double precision value in REG l. This is to divide the current integer value by of a power of 10 starting at 10e15 working its way down to 10e6 in a loop until the remainder is less than the current power).

12D1-12D2

JR NC,12CBH

Jump back to do another subtraction and keep looping until the CARRY FLAG gets set by the subtraction (meaning that the remainder is now less than the current power).

12D3

POP HL

Get the address of the power table from the stack and put it in register pair HL.

12D4-12D6

CALL 0D36H

GOSUB to 0D36H to add the double precision value pointed to by register pair HL (which is the table of powers of 10) to the double precision remainder in REG 1 to make it a positive value. Return with the correct remainder in REG 1.

12D7

EX DE,HL

Load register pair DE with the starting address for the current power of 10 (stored in register pair HL).

12D8

POP HL

Get the current input buffer address from the stack and put it in register pair HL.

12D9

LD (HL),B

Save the ASCII value for the digit in register B at the location of the input buffer pointer (stored in register pair HL).

12DA

INC HL

Bump the input buffer pointer in register pair HL since we have just put a digit there.

12DB

POP AF

Get the status flags from the stack and put it in register pair AF so that we can test for 10 times.

12DC

POP BC

Get the counts of digits before/after the decimal point value from the stack and put it in register pair BC.

12DD

DEC A

Decrement the counter value in register A (we are going to loop 10 times).

12DE-12DF

JR NZ,12C2H

Loop 10 times until the ASCII string has been figured.

12E0

PUSH BC

Save the the counts of digits before/after the decimal point value (stored in register pair BC) to the stack.

12E1

PUSH HL

Save the current input buffer pointer (stored in register pair HL) to the stack.

12E2-12E4

LD HL,411DH

Load register pair HL with the starting address for REG 1 (which holds the last half of the DOUBLE prevision value)
Note: 411DH-4124H holds REG l.

12E5-12E7

CALL 09B1H

Call 09B1H (which moves a SINGLE PRECISION number pointed to by HL to REG 1).

12E8-12E9

JR 12F6H

Jump to 12F6H to convert that last half to ASCII.

12EA - LEVEL II BASIC MATH ROUTINE - "FOUTCS"

This routine is to convert a SINGLE precision value to an INTEGER which will be the decimal digits. Divide the integer equivalent by 100,000 and 10,000. Use the code at 1335H to convert the last 1000 to ASCII.

12EA

PUSH BC

Save the leading digit count/comma count (in register pair BC) to the stack.

12EB

PUSH HL

Save the current input buffer pointer (stored in register pair HL) to the stack.

12EC-12EE

CALL 0708H

GOSUB to 0708H to add a single precision value of 0.5 to the single precision value in REG 1. The result is stored in BC/DE.

12EF

INC A

Bump the MSB.

12F0-12F2

CALL 0AFBH

GOSUB to 0AFBH to convert the positive single precision value in REG 1 to an integer. The result is stored in BC/DE.

12F3-12F5

GOSUB to 09B4H (which moves the SINGLE PRECISION value in DC/DE [which is the integer portion of the original single precision value] into REG 1).

12F6

POP HL

Get the current input buffer pointer value from the stack and put it in register pair HL.

12F7

POP BC

Get the leading digit count/comma count value from the stack and put it in register pair BC.

12F8

XOR A

Zero register A.

12F9-12FB

LD DE,13D2H

Load register pair DE with the starting address for a series of integer values (in this case, 100,000).

12FC

CCF

Complement the CARRY FLAG. This is the first time switch for the division loop of 12FC-1327H.

12FD-12FF

GOSUB to 1291H to put a decimal point or a comma into the input buffer if necessary .

1300

PUSH BC

Save the counts of digits before/after the decimal point value (stored in register pair BC) to the stack.

1301

PUSH AF

Save the CARRY FLAG for the count of the number of times through this loop (stored in register pair AF) to the stack.

1302

PUSH HL

Save the current input buffer pointer value (stored in register pair HL) to the stack.

1303

PUSH DE

Save the division table address (stored in register pair DE) to the stack.

1304-1306

GOSUB to 09BFH (which loads the SINGLE PRECISION value in REG 1 into register pair BC/DE).

1307

POP HL

Get the division table address (the integer value for 100,000) from the stack and put it in register pair HL.

1308-1309

LD B,2FH

Load register B with the ASCII value for a zero character minus one.

130AH - This routine divides the integer portion of the current value by 100,000 using compound subtraction. The quotient is kept in Register B as an ASCII value.

130A

INC B

Bump the ASCII value from the digit in register B to increase the ASCII value from 0 and upward.

130B

LD A,E

Load register A with the LSB of the single precision value in register E.

130C

SUB (HL)

Subtract the value at the location of the memory pointer in register pair HL (the LSB of 100,000) from the value of the LSB of the single precision value in register A.

130D

LD E,A

Load register E with the adjusted LSB of the single precision value in register A.

130E

INC HL

Bump the value of the memory pointer in register pair HL to the next digit of 100,000.

130F

LD A,D

Load register A with the NMSB of the single precision value in register D.

1310

SBC A,(HL)

Subtract the value at the location of the memory pointer in register pair HL (the middle byte of 100,000) from the value of the NMSB of the single precision value in register A.

1311

LD D,A

Load register D with the adjusted NMSB of the single precision value in register A.

1312

INC HL

Bump the value of the memory pointer in register pair HL to the MSB of 100,000.

1313

LD A,C

Load register A with the MSB of the single precision value in register C.

1314

SBC A,(HL)

Subtract the value at the location of the memory pointer in register pair HL from the value of the MSB of 100,000 (a single precision value in register A).

1315

LD C,A

Load register C with the adjusted MSB of the single precision value in register A.

1316

DEC HL

Decrement the value of the memory pointer in register pair HL to the NMSB of 100,000.

1317

DEC HL

Decrement the value of the memory pointer in register pair HL again, now to the LSB of 100,000.

1318-1319

JR NC,130AH

Loop until the ASCII value for the digit under 100,000 has been figured.

131A-131C

CALL 07B7H

We need to add 100,000 to C/DE and make it positive so we GOSUB to 07B7H to add the value at the location of the memory pointer in register pair HL to the value in register pairs BC and DE.

131D

INC HL

Bump the value of the memory pointer in register pair HL to now point to the 10,000 constant.

131E-1320

Save the remainder as a current value by GOSUB to 09B4H (which moves the SINGLE PRECISION value in DC/DE into REG 1).

1321

EX DE,HL

Load register pair DE with the address of the next value to divide the current value in REG 1 by (which is the constant of 10,000).

1322

POP HL

Get the value of the memory pointer from the stack and put it in register pair HL.

1323

LD (HL),B

Save the ASCII value for the digit in register B at the location of the input buffer pointer in register pair HL.

1324

INC HL

Bump the value of the input buffer pointer in register pair HL.

1325

POP AF

Get the CARRY FLAG from the stack and put it in register pair AF.

1326

POP BC

Get the value from the stack and put it in register pair BC so it can be saved later.

1327-1328

JR C,12FCH

If the CARRY FLAG is set, then reset it and loop the dividing by 10,000 until the integer portion is found.

1329

INC DE

If we fall through to here, we have divided the integer part of the single precision variable by 100,000 and then by 10,000 with the remainder being positive and saved as the current value. With this we bump the value of the memory pointer in register pair DE.

132A

INC DE

and again bump the value of the memory pointer in register pair DE, so now DE points to the constant 1,000.

132B-132C

LD A,04H

Load register A with the number of digits for the ASCII string to be figured.

132D-132E

JR 1335H

Jump down to 1335H to convert the remainder to 4 ASCII digits.

132FH - This routine will convert an INTEGER to ASCII.

132F

PUSH DE

Save the edit flags (stored in register pair DE) to the stack.

1330-1332

LD DE,13D8H

Load register pair DE with the starting address of the descending powers of 10 starting at 10,000.

1333-1334

LD A,05H

Load register A with the number of digits for the ASCII string to be built (i.e., 5).

1335H - This routine will convert the last x (based on A) digits of an INTEGER to ASCII.

1335-1337

Go put a decimal point or a comma into the input buffer if necessary.

1338

PUSH BC

Save the counts of digits before/after the decimal point value (stored in register pair BC) to the stack.

1339

PUSH AF

Save the number of digits counter (stored in register A) to the stack.

133A

PUSH HL

Save the address of the power table (stored in register pair HL) to the stack.

133B

EX DE,HL

Load register pair HL with the starting address of the descending powers of 10 starting at 10,000 (stored in register pair DE).

133C

LD C,(HL)

Load register C with the LSB for the power of 10 stored in register pair HL.

133D

INC HL

Bump the value of the memory pointer in register pair HL to be the MDB of the power of 10.

133E

LD B,(HL)

Load register B with the MSB for the integer value at the location of the memory pointer in register pair HL.

133F

PUSH BC

Save the integer value of the power of 10 in register pair BC to the stack.

1340

INC HL

Bump the value of the memory pointer in register pair HL to the next value in the power of 10 table.

1341

EX (SP),HL

Exchange the memory pointer of the next power of 10 (stored in register pair HL) with the value in the stack, and vice versa.

1342

EX DE,HL

Load register pair DE with the current value from the stack (stored in register pair HL).

1343-1345

LD HL,(4121H)

Load register pair HL with the integer value in REG 1.

1346-1347

LD B,2FH

Since we are about to start a loop which starts with an INC, compensate by loading register B with the ASCII value for a zero character minus one.

1348 - This loop divides the current value by a power of 10 starting at 10,000 and working down to 10. The remainder frome ach division is added to the division and the sum becomes the dividend for the next division until done. The quotient is +2FH (which is the ASCII equivalent of a quotient).

1348

INC B

Bump the ASCII value for the digit in register B (so it starts at 0 and moves up each loop).

1349

LD A,L

Load register A with the LSB of the integer value in register L.

134A

SUB E

Subtract the value of the LSB of the integer value in register E from the value of the LSB of the integer value in register A.

134B

LD L,A

Load register L with the adjusted value of the LSB of the integer value in register A.

134C

LD A,H

Load register A with the value of the MSB of the integer value in register H.

134D

SBC A,D

Subtract the MSB of the integer value in register D from the value of the MSB of the integer value in register A.

134E

LD H,A

Load register H with the adjusted value of the MSB of the integer value in register A.

134F-1350

JR NC,1348H

Loop back to 1348H until the CARRY FLAG is triggered because the quotient (stored in HL) is less than the current power of 10.

1351

ADD HL,DE

Add the remainder (stored as an integer in register pair DE) to the quotient (stored in register pair HL as an integer).

1352-1354

LD (4121H),HL

Save the integer remainder (stored in register pair HL) in REG 1.

1355

POP DE

Get the address of the next power of 10 from the stack and put it in register pair DE.

1356

POP HL

Get the memory pointer for the output buffer from the stack and put it in register pair HL.

1357

LD (HL),B

Save the ASCII value for the digit (from register B that tracked the number of divisions) to the location of the output buffer pointer (stored in register pair HL).

1358

INC HL

Bump the value of the input buffer pointer in register pair HL since we just filled that spot with an ASCII value.

1359

POP AF

Get the number of digits to convert from the stack and put it in A.

135A

POP BC

Get the counts of digits before/after the decimal point value from the stack and put it into register pair BC.

135B

DEC A

Decrement the value of the counter in register A (which is a countdown from 5).

135C-135D

JR NZ,1335H

If the counter of the number of digits (from 5) is still not zero, jump back to 1335H until all of the digits have been figured.

135E-1360

So now all the digits have been calculated in ASCII, so GOSUB 1291H to put a decimal point or comma into the input buffer if necessary.

1361

LD (HL),A

Save a zero (the value in register A which hit zero when the loop from 5 finished) to the input buffer, pointed to by register pair HL.

1362

POP DE

Get the value from the stack (which was whatever value was in DE when this routine started) and put it in register pair DE.

1363

RET

Return.

1364-136B - DOUBLE PRECISION CONSTANT STORAGE LOCATION

1364-136BH

00 00 00 00 F9 02 15 A2

A double precision constant equal to 1E10 (or 10 x 10E9)is stored here.

136C-1373 - DOUBLE PRECISION CONSTANT STORAGE LOCATION

136C-1373H

FD FF 9F 31 A9 5F 63 B2

A double precision constant equal to 9.9921E14 (or 1 x 10e15) is stored here.

1374-137B - DOUBLE PRECISION CONSTANT STORAGE LOCATION

1374-137BH

FE FF 03 BF C9 1B 0E B6

A double precision constant equal to 1x10^16 is stored here.

137C-1383 - DOUBLE PRECISION CONSTANT STORAGE LOCATION

137C-1383H

00 00 00 00 00 00 00 80

A double precision constant equal to 0.5 is stored here.
BYTE SAVING NOTE: Referencing 1380H, which is half-way through this double precision value of .5, results in a single precision value of 0.5.

1384-138B - DOUBLE PRECISION CONSTANT STORAGE LOCATION

1384-138BH

00 00 04 BF C9 1B 0E B6

A double precision constant equal to 1x10^16 is stored here.

138A-138DH

0E B5 00 80

BYTE SAVING NOTE: A double precision constant equal to .502778.

138C-13D1 - DOUBLE PRECISION INTEGER CONSTANT STORAGE LOCATION

138C-1392H

00 80 C6 A5 7E 8D 03

1 x 10e15.

1393-1399H

00 40 7A 10 F3 5A 00

1 x 10e14.

139A-13A0H

00 A0 72 4E 18 09 00

1 x 10e13.

13A1-13A7H

00 10 A5 D5 E8 00 00

1 x 10e12.

13A1-13A7H

00 10 A5 D5 E8 00 00

1 x 10e12.

13A8-13AEH

00 E8 76 48 17 00 00

1 x 10e11 (which is 100,000,000,000).

13AF-13B5H

00 E4 0B 54 02 00 00

1 x 10e10 (which is 10,000,000,000).

13B6-13BCH

00 CA 9A 3B 00 00 00

1 x 10e09 (which is 1,000,000,000).

13BD-13C3H

00 E1 F4 05 00 00 00

1 x 10e08 (which is 100,000,000).

13C4-13CAH

80 96 98 00 00 00 00

1 x 10e07 (which is 10,000,000).

13CB-13D1H

40 42 0F 00 00 00 00

1 x 10e06 (which is 1,000,000).

13D2H-13D9H - SINGLE PRECISION INTEGER CONSTANT STORAGE LOCATION

13D2-13D4H

A0 86 01

1 x 10e04 (which is 100,000).

13D5-13D7H

10 27 00

1 x 10e03 (which is 10,000).

13D8-13D9H

E8 03

1 x 10e02 (which is 1,000).

13DA-13DBH

E8 03

1 x 10e01 (which is 100).

13DEH

1 x 10e00 (which is 10).

13DF

NOP

Nothing.

13E1-13E6 - LEVEL II BASIC MATH ROUTINE

13E1

NOP

Do nothing.

13E2-13E4

LD HL,0982H

Load register pair HL with 0982H.
NOTE: 0982H is the address of the routine for conversion of floating point numbers from negative to positive.

13E5

EX (SP),HL

Exchange the value of that routines jump address to the stack with the value of the return address in register pair HL.

13E6

JP (HL)

Jump to the address in register pair HL, which is basically a return to caller.

13E7-13F1 - LEVEL II BASIC SQR(n) - "SQR"

This routine computes the square root of any value in ACCumulator. It processes it by raising n to the power of 0.5. The root is left in ACCumulator as a single precision value. Single-precision values only should be used

13E7-13F1

GOSUB 09A4 which moves the SINGLE PRECISION value in REG 1 to the stack (stored in LSB/MSB/Exponent order).

13EA-13EC

LD HL,1380H

Load register pair HL with the starting address of a single precision constant equal to 0.5 (which will be the exponent).

13ED-13EF

CALL 09B1H

GOSUB 09B1H (which moves a SINGLE PRECISION number pointed to by HL to REG 1).

13F0-13F1

JR 13F5H

Jump to the EXP(n) routine at 13F5H (which will be using a .5 exponent to do the square root) skipping 13F2H since the exponent is already single precision.

13F2-1478H - LEVEL II BASIC X to the Y Power (X^Y) ROUTINE - "FPWRQ"

A call to 13F2H raises the single precision value which has been saved to the STACK to the power specified in ACCumulator. The result will be returned in ACCumulator. The method of computation is e ** (y ln x).

13F2-13F4

CALL 0AB1H

Make sure that the exponent is single precision by GOSUB to 0AB1H which is the CONVERT TO SINGLE PRECISION routine at 0AB1H (which converts the contents of REG 1 from integer or double precision into single precision).

13F5

POP BC

Get the MSB of the single precision value from the stack and put it in register pair BC.

13F6

POP DE

Get the NMSB and the LSB of the single precision value from the stack and put it in register pair DE.

NOTE: To use a ROM call to raise a single precision number (the base) to a single precision power (the exponent), store the base (single precision) in registers BCDE, and store the exponent (also single precision) in 4121H-4124H and then CALL 13F7H. The result (in single precision format) is in 4121H-4124H and in approximately 50 milliseconds.

13F7-13F9

GOSUB 0955H to check the sign for the single precision value in REG 1 (the exponent).

13FA

LD A,B

Load register A with the MSB of the number to be raised (stored as a single precision value in register B).

13FB-13FC

JR Z,1439H

Jump to the EXP(n) routine at 1439H if the exponent (the single precision value in REG 1) is equal to zero.

13FD-13FF

JP P,1404H

Skip the next 2 opcodes (which check to see if zero is involved) if the exponent (the single precision value in REG 1) is positive.

1400

OR A

Check to see if the value to be raised (i.e., the single precision value in register pairs BC and DE) is equal to zero.

1401-1403

JP Z,199AH

Display a ?/0 ERROR message if the single precision value in REG 1 is negative and the single precision value in register pairs BC and DE is equal to zero.
/0 ERROR entry point.

1404

OR A

ANOTHER check to see if the value to be raised (i.e., the single precision value in register pairs BC and DE) is equal to zero.

1405-1407

JP Z,0779H

Jump to 0779H if the value to be raised (i.e., the single precision value in register pairs BC and DE) is equal to zero.

1408

PUSH DE

At this point we know that none of the values are zero, and we are raising the number to a positive power. Save the value to be raised (the NMSB and the LSB of the single precision value in register pair DE) to the stack.

1409

PUSH BC

Save the exponent and the MSB of the single precision value in register pair BC to the stack.

140A

LD A,C

Load register A with the value of the MSB of the single precision value to be raised (which is stored in register C).

140B-140C

OR 7FH

Test the sign of the based by turning on bits 0-6 of the MSB of the single precision value (0111 1111) in register A.

140D-140F

Load the exponent (the power) into BC/DE by GOSUB to 09BF which loads the SINGLE PRECISION value in REG 1 (the exponent) into register pair BC/DE.

1410-1412

JP P,1421H

Jump down to 1421H if the base (the single precision value to the stack) is positive.

1413

PUSH DE

Save the NMSB and the LSB of the exponent (the single precision value in register pair DE) to the stack.

1414

PUSH BC

Save the exponent and the LSB of the single precision value in register pair BC to the stack.

1415-1417

CALL 0B40H

GOSUB to 0B40H to figure the integer portion of the exponent (i.e., the single precision value in REG 1) into A with the truncated floating point portion into REG 1.

1418

POP BC

Restore the exponent and the MSB of the single precision value from the stack and put it in register pair BC.

1419

POP DE

Restore the NMSB and the LSB of the single precision value from the stack and put it in register pair DE.

141A

PUSH AF

Save the integer portion of the exponent (i.e., the value in register pair AF) to the stack.

141B-141D

Compare the original exponent to the truncated one by GOSUB to 0A0CH.

NOTE: The routine at 0A0CH algebraically compares the single precision value in BC/DE to the single precision value REG 1.
The results are stored in A as follows:

A=00H if REG 1 = BCDE
A=01H if REG 1>BCDE; and
A=FFH if REG 1<BCDE.

141E

POP HL

Get the exponent as an integer from the stack and put it in register H.

141F

LD A,H

Load register A with the exponent as an integer (as stored in register H).

1420

RRA

If the exponent (as an integer) is odd, set the CARRY FLAG.

1421

POP HL

Get the original exponent from the stack and put it in register pair HL.

1422-1424

LD (4123H),HL

Save the value of the original exponent and the MSB of the single precision value (stored in register pair HL) in REG 1.

1425

POP HL

Get the rest of the exponent from the stack and put it in register pair HL.

1426-1428

LD (4121H),HL

Save the rest of the exponent (i.e., as stored in register pair HL as the NMSB and the LSB of the single precision value) in REG 1.

1429-142B

CALL C,13E2H

If the CARRY FLAG is set (i.e. the exponent is odd and the base is negative) GOSUB to 13E2H.

142C-142E

CALL Z,0982H

If the exponent is an integer and the base is negative, GOSUB to 0983H to invert the value of the exponent.

142F

PUSH DE

Save the NMSB and the LSB of the exponent (i.e., the single precision value in register pair DE) to the stack.

1430

PUSH BC

Save the MSB of the exponent (i.e., the single precision value in register pair BC) to the stack.

1431-1433

CALL 0809H

CALL the LOG(N) routine at 0809H (which computes the natural log (base E) of the single precision value in REG 1. The result is returned as a single precision value in REG 1. Can give an ILLEGAL FUNCTION CALL erro if a negative base is raised to a power with a fraction).

1434

POP BC

Get the exponent and the MSB of the single precision value from the stack and put it in register pair BC.

1435

POP DE

Get the NMSB and the LSB of the single precision from the stack and put it in register pair DE.

1436-1438

We need to multiply the ln(value) * the exponent so we have to GOSUB to 0847H to SINGLE PRECISION MULTIPLY routine (which multiplies the current value in REG 1 by the value in (BC/DE). The product is left in REG 1.

1439 - EXP routine. Single-precision only. (REG 1 = EXP(REG1)).

A call to 1439H raises E (natural base) to the value in REG 1 which must be a single precision value. The result will be returned in REG 1 as a single precision number.

NOTE: To use a ROM call to find EXP(X), where X is a single precision variable, store the value of X in 4121H-4124H and then CALL 1439H. The result (in single precision format) is in 4121H-4124Hin approximately 28 milliseconds. NOTE: A fatal error occurs if the result is as large as 2 to the power of 127.

1439-143BHEXP

Call 09A4 to move the SINGLE PRECISION value in REG 1 (the exponent) to the stack (stored in LSB/MSB/Exponent order).

143C-143E

LD BC,8138H

Load register pair BC with the exponent and MSB of a single precision constant.

143F-1441

LD DE,AA3BH

Load register pair DE with the NMSB and the LSB of a single precision constant. Register pairs BC and DE are now equal to a single precision constant of 1.442695 (which is approximately 2 + ln 2).

1442-1444

We need to multiply the exponent value by 2 ln 2 so we call the SINGLE PRECISION MULTIPLY routine at 0847H (which multiplies the current value in REG 1 by the value in (BC/DE). The product is left in REG 1.

1445-1447

LD A,(4124H)

Load register A with the result of the math just done (i.e., which was multiplying the exponent value by 2 ln 2) which was stored in REG 1.

1448-1449

CP 88H

Check to see if the integer portion of the single precision value in REG 1 uses more than 7 bits of precision by comparing it against a mask of 1000 1000.

144A-144C

JP NC,0931H

Jump to 0931H if the single precision value in REG 1 uses more than 7 bits of precision for its integer portion.

144D-144F

CALL 0B40H

So now that we know the integer portion is less than 8 bits, we need to get the integer and put it into Register A by GOSUB to 0B40H to get the integer portion of the value in REG 1 and return with it in register A.

1450-1451

ADD A,80H

Adjust the value in register A by masking it against 80H (Binary: 1000 0000).

1452-1453

ADD A,02H

Adjust the value in register A by adding 2 more (Binary: 1000 0010).

1454-1456

JP C,0931H

If (exponent * 2 ln 2) is => 126 (meaning when 2 was added it it, it overflowed with a 128), jump to 0931H.

1457

PUSH AF

Save the integer value (+82H) (as stored in register pair AF) to the stack.

1458-145A

LD HL,07F8H

Load register pair HL with a single precision constant equal to 1.0 (as found at 1458H).

145B-145D

Go add the single precision constant 1.0 (as pointed to by register pair HL) to the current value in REG 1 which is EXP * 2 ln 2.

145E-1460

CALL 0841H

Need to multiply that by ln 2, so GOSUB to 0841H to multiply (1 + [EXP * 2 ln 2]) (as stored in REG 1) by 0.693147.

1461

POP AF

Get the integerized value of EXP * 2 ln 2 (as stored in the stack) and put it in register pair AF.

1462

POP BC

Get the original exponent into BC/DE in 2 steps fist get the exponent and the MSB of the single precision value from the stack and put it in register pair BC ...

1463

POP DE

and then get the NMSB and the LSB of the single precision value from the stack and put it in register pair DE.

1464

PUSH AF

Save the integerized EXP * 2 ln 2 (stored in register pair AF) to the stack.

1465-1467

CALL 0713H

Now we need to subtract the original exponent from the integerized exponent so we GOSUB to 0713H which is the SINGLE PRECISION SUBTRACT routine (which subtracts the single precision value in BC/DE from the single precision value in REG 1. The difference is left in REG 1).

1468-146A

CALL 0982H

To force that difference to be a positive number we GOSUB to 0982H which makes the current single precision value in REG 1 positive.

146B-146D

LD HL,1479H

Load register pair HL with the starting address for a series of 8 coefficients.

146E-1470

CALL 14A9H

GOSUB to 14A9H to do that series of computations.

1471-1473

LD DE,0000H

We need to load the integerized equivalent of EXP * 2 lnt 2 into BC/DE so first we load register pair DE with zero ...

1474

POP BC

... and then get the value from the stack and put it in register pair BC.

1475

LD C,D

Load register C with zero (since Register D was filled with a zero in 1471H).

1476-1478

JP 0847H

We need to multiply by the sum from the series and return so we jump to 0847H which is the the SINGLE PRECISION MULTIPLY routine at 0847H (which multiplies the current value in REG 1 by the value in (BC/DE). The product is left in REG 1.

1479-1499 - SINGLE PRECISION CONSTANT STORAGE LOCATION
This represents 1/6, -1/5, 1/4, -1/3, 1/2, -1, and 1

1479H

The number of single precision constants (9) which follow are stored here.

147A-147DH

40 2E 94 74

A single precision constant equal to -0.00014171607 (-1.413165 * 10e-4) is stored here.

147E-1481H

70 4F 2E 77

A single precision constant equal to 0.00132988204 (1.32988 * 10e-3, roughly -1/6) is stored here.

1482-1485H

6E 02 88 7A

A single precision constant equal to -0.00830136052 (-8.30136 * 10e-3, roughly -1/5) is stored here.

1486-1489H

E7 A0 2A 7C

A single precision constant equal to 0.04165735095 (roughly 1/4) is stored here.

148A-148DH

50 AA AA 7E

A single precision constant equal to -0.16666531543 (roughly -1/3) is stored here.

148E-1491H

FF FF 7F 7F

A single precision constant equal to 0.49999996981 (roughly 1/2) is stored here.

1492-1495H

00 00 80 81

A single precision constant equal to -1.0 is stored here.

1496-1499H

00 00 00 81

A single precision constant equal to 1.0 is stored here.

149A-14C8 - LEVEL II BASIC MATH ROUTINE

This is a general purpose summation routine which computes the series SUM ((((x^2 * c0+c1)x^2 +c2)x^2 + ... cN)x for I=0 to N when entered at 149AH If entered at 14A9H the series changes to SUM ((((x*c0+c1)x*c2)x+c3)x+...cN. On entry, the x is held in BC/DE and HL points to a list containing the number of terms followed by the coefficients.

149A-149C

GOSUB to 09A4 to which move the SINGLE PRECISION value in REG 1 to the stack (stored in LSB/MSB/Exponent order).

149D-149F

LD DE,0C32H

Load register pair DE with the return address of 0C32H.
NOTE: 0C32H pops BC and DE and then JUMPs to JP 0847H.

14A0

PUSH DE

Save DE to the STACK.

14A1

PUSH HL

Save the memory pointer of list containing the number of terms followed by the coefficients (as stored in register pair HL) to the stack.

14A2-14A4

GOSUB to 09BFH which loads the SINGLE PRECISION value in REG 1 into register pair BC/DE.

14A5-14A7

Since REG 1 and BC/DE now hold the same number, you can square that by a GOSUB to 0847H which is the SINGLE PRECISION MULTIPLY routine (which multiplies the current value in REG 1 by the value in (BC/DE). The product is left in REG 1).

14A8

POP HL

Restore the address of the coefficient from the stack and put it in register pair HL.

14A9-14AB

We need to move either x or x**2 (depending on the routine entry point) to the stack so we GOSUB to 09A4 which moves the SINGLE PRECISION value in REG 1 to the stack (stored in LSB/MSB/Exponent order).

14AC

LD A,(HL)

Load register A with the number of values to be figured at the location of the memory pointer in register pair HL.

14AD

INC HL

Bump the value of the memory pointer in register pair HL so that it points to the next coefficient.

14AE-14B0

CALL 09B1H

Now load the coefficient (stored in HL) and move it to REG 1 by GOSUB to 09B1H (which moves a SINGLE PRECISION number pointed to by HL to REG 1).

14B1H

06 F1

Z-80 Trick! See the general explanation at 10F8H.

14B2

POP AF

Get the count of coefficients left (from the stack) and put it in register A.

14B3-14B4

POP BC
POP DE

Get the value of x from the stack and put it in register pair BC/DE.

14B5

DEC A

Count 1 of the terms as computed by decrementing the counter in register A.

14B6

RET Z

If that decrement results in a zero (meaning the series of computations has been completed) return out of the subroutine.

14B7-14B8

PUSH DE
PUSH BC

Save the NMSB and the LSB of x from DE to the stack and save the MSB of x from BC to the stack.

14B9

PUSH AF

Save counter of remaining terms to compute (stored in register A) to the stack.

14BA

PUSH HL

Save the value of the memory pointer to the next coefficient (stored in register pair HL) to the stack.

14BB-14BD

Compute C(I)*x by GOSUB to 0847H which is the SINGLE PRECISION MULTIPLY routine (which multiplies the current value in REG 1 by the value in (BC/DE). The product is left in REG 1.

14BE

POP HL

Restore the coefficient table address (from the stack) to register pair HL.

14BF-14C1

CALL 09C2H

Get the next coefficient from HL into BC/DE by GOSUB to 09C2H (which loads a SINGLE PRECISION value pointed to by register pair HL into register pairs BC and DE).

14C2

PUSH HL

Save the next coefficient (stored in register pair HL) to the stack.

14C3-14C5

CALL 0716H

Compute C(I)*x+C(I+1) by GOSUB to 0716H which is the SINGLE PRECISION ADD routine (which adds the single precision value in (BC/DE) to the single precision value in REG 1. The sum is left in REG 1).

14C6

POP HL

Restore the coefficient table address (from the stack) to register pair HL.

14C7-14C8

JR 14B2H

Jump back to 14B2H to continue the series. REG 1 contains the current term.

14C9-1540 - LEVEL II BASIC RND(n). Generates a single-precisions random number between 0 and 1, or 1 and n depending on the parameter passed in REG 1, The random value is returned in REG 1 as an integer with the mode flag set. The parameter passed will determine the range of the random number returned. A parameter of 0 will return an interger between 0 and 1. A parameter greater than 0 will have any fraction portion truncated and will cause a value between 1 and the integer portion of the parameter to be returned.

NOTE: To run a RND(J) function via a ROM call just The RND(J) function (with J a nonzero integer) load the value of J into the HL register pair. Then CALL 14CCH and then CALL 0A7FH. The result (in integer format) is in 4121H-4122H and in HL in approximately 5.7 milliseconds. The input variable J must have a value between 1 and 32767, inclusive, or an FC error will occur.

14C9-14CBHRNDM

CALL 0A7FH

Call the CONVERT TO INTEGER routine at 0A7FH (where the contents of REG 1 are converted from single or double precision to integer and deposited into HL).

14CC

LD A,H

Load register A with the value of the MSB for the integer value in register H.

14CD

OR A

Check to see if the integer value in register pair HL is negative.

14CE-14D0

JP M,1E4AH

Display a ?FC ERROR message if the integer value in register pair HL is negative.

14D1

OR L

To test for HL=0, the opcode pair of LD A,H / OR L is a simplest way. Only if both H and L are zero, will A be zero.

14D2-14D4

JP Z,14F0H

If it is zero, we don't need the rest of the below which functions to generate RND(n) so we just jump to 14F0H (which generates RND(0)) if the integer value in register pair HL is equal to zero (meaning the call was for RND(0)).

14D5

PUSH HL

Since it wasn't zero, we need to save the n of RND(n) (as stored in register pair HL) to the stack.

14D6-14D8

CALL 14F0H

GOSUB to 14F0H (which generates RND(0)) and return with the single precision result in REG 1.

14D9-14DB

Load the random number into BC/DE by a GOSUB to 09BFH which loads the SINGLE PRECISION value in REG 1 into register pair BC/DE.

14DC

EX DE,HL

Load register pair HL with the NMSB and the LSB of the single precision value in register pair DE.

14DD

EX (SP),HL

Exchange the integer value to the stack with NMSB and the LSB of the single precision value in register pair HL. At this point, the random number is in the stack and the n (of RND(n)) is stored in register pair HL.

14DE

PUSH BC

Save the RND(0) value to the stack.

14DF-14E1

CALL 0ACFH

Convert the original x of RND(x) to single precision by GOSUB to 0ACFH which converts the integer value in register pair HL to single precision and return with the result in REG 1.

14E2-14E3

POP BC
POP DE

Restore the RND(0) value from the stack and put it into register pair BC/DE.

14E4-14E6

Multiply the RND(0) value (currently in BC/DE) by the n of RND(n) (currently in REG 1) by GOSUB to 0847H which is the SINGLE PRECISION MULTIPLY routine (which multiplies the current value in REG 1 by the value in (BC/DE). The product is left in REG 1.

14E7-14E9

LD HL,07F8H

Load register pair HL with the starting address of a single precision constant equal to 1.0.

14EA-14EC

Increase the random number by one by GOSUB to 070BH which adds the single precision constant pointed to by register pair HL (which is 1.0) to the single precision value in REG 1 (which is the random number). Return with the single precision result in REG 1

14ED-14EF

JP 0B40H

With the random number now in REG 1, jump to 0B40H (which will convert it to an integer and RETurn to the subroutine caller).

14F0H - This routine calculates RND(0).

NOTE: To run a RND(0) function via a ROM call just CALL 14F0H. No input variable is necessary. The result (in single precision format) is in 4121H-4124H in approximately 2.4 milliseconds.

14F0-14F2

LD HL,4090H

Load register pair HL with the starting address for a table used for figuring random numbers.
NOTE: 4090H holds the random number seed 2

14F3

PUSH HL

Save the starting address for a table used for figuring random numbers (stored in HL) to the stack.

14F4-14F6

LD DE,0000H

Load register pair DE with zero (which will be the NMLSB and LSB of the starting value).

14F7

LD C,E

Load register C with zero (C will be the MSB of the starting value).

14F8-14F9

LD H,03H

Load register H with the counter value for the loop (which will be 3).

14FA-14FB

LD L,08H

Load register L with a counter value of 8.

14FC

EX DE,HL

Exchange the counters in register pair HL with the NMSB and the LSB of the random number in register pair DE.

14FD

ADD HL,HL

Multiply the NMSB and the LSB of the random number in register pair HL by two.

14FE

EX DE,HL

Exchange the NMSB and the LSB of the random number in register pair HL with the counters in register pair DE.

14FF

LD A,C

Load register A with the MSB of the random number in register C.

1500

RLA

Multiply the MSB of the random number in register A by two.

1501

LD C,A

Load register C with the adjusted MSB of the random number in register A.

1502

EX (SP),HL

Exchange the counter values in register pair HL with the value of the memory pointer to the stack.

1503

LD A,(HL)

Load register A with the table value (held at the location of the memory pointer in register pair HL).

1504

RLCA

Multiply the value in register A by two.

1505

LD (HL),A

Save the doubled value (stored in register A) at the location of the memory pointer in register pair HL.

1506

EX (SP),HL

Exchange the memory pointer in register pair HL with the counter values to the stack.

1507-1509

JP NC,1516H

Jump forward to 1516H if the table value hasn't overflowed.

150A

PUSH HL

If we are here, the table value overflowed so we need to save the counter values in register pair HL to the stack.

150B-150D

LD HL,(40AAH)

Load register pair HL with the NMSB and the LSB of the random number seed.
NOTE: 40AAH-40ADH holds the random number seed.

150E

ADD HL,DE

Add the NMSB and the LSB of the random number in register pair DE to the NMSB and the LSB of the random number seed in register pair HL.

150F

EX DE,HL

Load register pair DE with the adjusted NMSB and LSB of the random number in register pair HL.

1510-1512

LD A,(40ACH)

Load register A with the MSB of the random number seed.

1513

ADC A,C

Add the MSB of the random number in register C to the MSB of the random number seed in register A.

1514

LD C,A

Load register C with the adjusted MSB of the random number in register A.

1515

POP HL

Get the counter values from the stack and put it in register pair HL.

1516

DEC L

Decrement the loop counter in register L.

1517-1519

JP NZ,14FCH

Loop back to 14FCH until the above has been done eight times.

151A

EX (SP),HL

Exchange the counter values in register pair HL with the memory pointer of the table value to the stack.

151B

INC HL

Bump to the next table value.

151C

EX (SP),HL

Exchange the value of the table value in register pair HL with the counter value to the stack.

151D

DEC H

Decrement the counter value of the outer loop (in register H).

151E-1520

JP NZ,14FAH

Loop back to 14FAH three times until the random number has been figured.

1521

POP HL

Clear the flag table address from the stack. The fact that it is going into HL is not important.

1522-1524

LD HL,B065H

Load register pair HL with the value to reseed the random number seed.

1525

ADD HL,DE

Add the seed (from register pair HL) to the NMSB and the LSB of the random number in register pair DE.

1526-1528

LD (40AAH),HL

Save the adjusted value in register pair HL as the NMSB and the LSB of the random number seed.
NOTE: 40AAH-40ADH holds the random number seed.

1529-152B

CALL 0AEFH

Go set the current number type to single precision.

152C-152D

LD A,05H

Load register A with a 5.

152E

ADC A,C

Add 5 (the value held in A) and the MSB of the random number in register C.

152F-1531

LD (40ACH),A

Save the adjusted value in register A as the MSB of the random number seed.

1532

EX DE,HL

Swap DE and HL so as to move the NMSB and LSB to DE so that we will have a BC/DE pair for the random number.

1533-1534

LD B,80H

Load register B with a value for the sign flag and the exponent (Binary: 1000 0000).

1535-1537

LD HL,4125H

Load register pair HL with the address for the sign value storage location.
NOTE: 4125H-4126H is used by floating point routines.

1538

LD (HL),B

Save the sign result (1000 0000) in register B at the location of the memory pointer in register pair HL.

1539

DEC HL

Decrement to exponent (held in register pair HL).

153A

LD (HL),B

Set the exponent to (1000 0000) so that the value will be < 1.

153B

LD C,A

Load register C with the value of the MSB for the single precision random number in register A.

153C-153D

LD B,00H

Zero the value of the exponent in register B.

153E-1540

JP 0765H

Jump to 0765H which will normalize the value and then jump to 14D9H unless RND(0) was called in which case return to caller.

1541-1546 - LEVEL II BASIC COS

COS routine. Single-precision only.(REG 1 = COS(REG 1)).
A call to 1541H computes the cosine for an angle given in radians. The angle must be a floating point value in REG 1; the cosine will be returned in REG 1 as a floating point value.

NOTE: To use a ROM call to find COS(X), where X is a single precision variable (in radians), store the value of X in 4121H-4124H and then CALL 1541H. The result (in single precision format) is in 4121H-4124Hin approximately 25 milliseconds.

1541-1543HCOSN

LD HL,158BH

Load register pair HL with the starting address of a single precision constant equal to 1.57079637029 (which is pi / 2).

1544-1546

GOSUB to 070BH to add 1.57079637029 (stored in HL) to the single precision value in REG 1 and then pass through to the SIN() routine which is next.

1547-158A - LEVEL II BASIC SIN

SIN(n) routine. Single-precision only.(REG 1 = SIN(REG 1)).

A call to 1549H returns the sine as a single precision value in REG 1. The sine must be given in radians in REG 1.

The actual calculation routine is:

Assume X <= 360 degrees.

Recompute x as x=x/360 so that x=< 1.

If x <= 90 degrees go to step 7.

If x <= 180 degrees then x=0.5-x and then go to step 7.

If x <= 270 degrees then x=0.5-x.

Recompute x as x=x-1.0.

Compute SIN using the power series.

NOTE: To use a ROM call to find SIN(X), where X is a single precision variable, store the value of X in 4121H-4124H and then CALL 1547H. The result (in single precision format) is in 4121H-4124Hin approximately 25 milliseconds. NOTE: The argument (X) must be in radians.

1547-1549HSINE

Call 09A4 which moves the SINGLE PRECISION value in REG 1 (the x in a SIN(x) call) to the stack (stored in LSB/MSB/Exponent order).

154A-154C

LD BC,8349H

Load register pair BC with the exponent and the MSB of a single precision constant.

154D-154F

LD DE,0FDBH

Load register pair DE with the NMSB and the LSB of a single precision constant. Register pairs BC and DE now hold a single precision constant equal to 6.2831855 (which is pi * 2).

1550-1552

Move 2 x pi value (held in DC/BE) into REG 1 by GOSUB to 09B4H (which moves the SINGLE PRECISION value in DC/DE into REG 1).

1553-1554

POP BC
POP DE

Put the x from a SIN(x) call into BC/DE.

1555-1557

CALL 08A2H

To divide the x from a SIN(x) call (held in BC/DE) by pi*2 (held in REG 1) we must GOSUB 80A2H to divide the single precision value in register pairs BC and DE by the single precision value in REG 1. Return with the single precision result in REG 1.

1558-155A

Move that value (x / 2*pi) from REG 1 to the stack by GOSUB to 09A4H which moves the SINGLE PRECISION value in REG 1 to the stack (stored in LSB/MSB/Exponent order).

155B-155D

CALL 0B40H

Go figure the integer portion for the single precision value in REG 1 by calling 0B40H. We need to do this so we can isolate the remainder.

155EH,155F

POP BC
POP DE

Put the quotient and remainder of x/2*pi into BC/DE.

1560-1562

CALL 0713H

To get the remainder we need to subtract the integer portion from the full portion so we GOSUB 0713H (the SINGLE PRECISION SUBTRACT routine) to subtract the single precision value in BC/DE (the entire result) from the single precision value in REG 1 (the integer part of the result). The difference is left in REG 1).

1563-1565

LD HL,158FH

Load register pair HL with the starting address of a single precision constant equal to 0.25.

1566-1568

CALL 0710H

Next in calculating a SIN we would need to subtract .25 (held in HL) from the fractional part (held in REG 1) so as to see if it is <= to 90 degrees. To do this we GOSUB 0710H to subtract the single precision value in REG 1 from the single precision constant pointed to by register pair HL. Return with the result in REG 1.

1569-156B

Go check the sign of the result of that (.25 - fractional part) subtraction which is held in REG 1.

156C

SCF

Set the CARRY FLAG.

156D-156F

JP P,1577H

Jump to 1577H if the single precision value in REG 1 is positive (meaning it is < than 90 degrees).

1570-1572

CALL 0708H

If we are here, it is => 90 degrees, so we need to add .5 to the single precision value in REG 1. Return with the result in REG 1

1573-1575

Go check the sign for the single precision value in REG 1 which basically checks to see if it is > 0.75 (meaning < 270 degrees).

1576

OR A

Test the value of the sign test in register A.

1577

PUSH AF

Save the sign indicator (+ or -1) in register pair AF to the stack.

1578-157A

CALL P,0982H

If it is positive, make it negative by GOSUB to 0982H.

157B-157D

LD HL,158FH

Load register pair HL with the starting address of a single precision constant equal to 0.25.

157E-1580

Add .25 (stored in HL) to the current value in REG 1 by GOSUB to 070BH (result is saved in REG 1).

1581

POP AF

Get the sign reversal flag from the stack and put it in register pair AF.

1582-1584

CALL NC,0982H

Set the sign of the x term according to the quadrant by GOSUB to 0982H if if the CARRY FLAG wasn't set from above.

1585-1587

LD HL,1593H

Load register pair HL with 1593H (which is the starting address for a series of single precision values for a set of computations).

1588-158A

JP 149AH

JUMP to 149AH to compute the series and then RETURN.

158BH-15A7H - SINGLE PRECISION CONSTANT STORAGE LOCATION

158B-158EH

DB 0F 49 81

A single precision constant equal to 1.57079637029 is stored here.

158F-1592H

00 00 00 7F

A single precision constant equal to 0.25 is stored here.

1593H

05H

The number of single precision constants (05) which follows is stored here. These are the coefficients used in the power series to compute SIN(x).

1594-1597H

BAH D7H 1EH 86H

A single precision constant equal to 39.7106704708 is stored here.

1598-159BH

64H 26H 99H 87H

A single precision constant equal to -76.5749816893 is stored here.

159C-159FH

58H 34H 23H 87H

A single precision constant equal to 81.6022338865 is stored here.

15A0-15A3H

E0H 6DH A5H 86H

A single precision constant equal to -41.3416748045 is stored here.

15A4-15A7H

DAH 0FH 49H 83H

A single precision constant equal to 6.28318500497 is stored here.

15A8-15BC - LEVEL II BASIC TAN ROUTINE TAN(n) - "TAN"

Single-precision only.(REG 1 = TAN(REG 1)).
A call to 15A8H computes the tangent of an angle in radians. The angle must be specified as a single precision value in REG 1. The tangent will be left in REG 1.
Uses the fact that TAN(x) = SIN(x) / COS(x)

NOTE: To use a ROM call to find TAN(X), where X is a single precision variable (in radians), store the value of X in 4121H-4124H and then CALL 15A8H. The result (in single precision format) is in 4121H-4124Hin approximately 54 milliseconds. NOTE: A fatal error occurs if the result is as large as 2 to the power of 127, which will be the case if the value of X is sufficiently close to any odd multiple of pi/2 radians.

15A8-15AA

Call 09A4 which moves the SINGLE PRECISION value in REG 1 to the stack (stored in LSB/MSB/Exponent order).

15AB-15AD

CALL 1547H

Call the SIN(n) routine at 1547H (which returns the sine as a single precision value in REG 1. The sine must be given in radians in REG 1.

15AEH,15AF

POP BC
POP HL

Get the original exponent and value from the stack and put it in register pair BC/HL.

15B0-15B2

Call 09A4 which moves the SIN(x) single precision value (stored in REG) 1 to the stack (stored in LSB/MSB/Exponent order).

15B3

EX DE,HL

Load register pair DE with the NMSB and the LSB of the single precision value in register pair HL.

15B4-15B6H

Call 09B4H (which moves the original value in BC/DE into REG 1).

15B7-15B9

CALL 1541H

Call the COSINE routine at 1541H (which computes the cosine for an angle given in radians. The angle must be a floating point value; the cosine will be returned in REG 1 as a floating point value.

15BA-15BC

JP 08A0H

Jump to 08A0H to compute SIN(n) / COS(n) and return the value as TAN(n).

15BD-15E2 - LEVEL II BASIC ATN ROUTINE ATN(n) routine - "ATAN".

Single-precision only.(REG 1 = ATN(REG 1)).
A call to 15BD returns the angle in radians, for the floating point tangent value in REG 1. The angle will be left as a single precision value in REG 1.
The method of computation used in this routine is:

Test the sign of the tangent to see if a negative angle is in the 2nd or 4th quadrant. Set the flag to force the result to positive on exit. If the value is negative, invert the sign.

Test magnitude of tangent. If it is < 1 go to step 3. Otherwise, compute its reciprocal and put the return address on the stack that will calculate pi/2 - series value.

Evaluate the series: (((x^2*c0+c1) x^2+c2) ... c8)x

If the flag from step 1 is not set, then invert the sign of the series result.

If the original value is < 1 then return to the caller. Otherwise, compute pi/2-value from step 4 and then return.

NOTE: To use a ROM call to find ATN(X), where X is a single precision variable, store the value of X in 4121H-4124H and then CALL 15BDH. The result (in single precision format, in radians) is in 4121H-4124Hin approximately 27 milliseconds.

15BD-15BF

Go check the sign of the single precision value in REG 1

15C0-15C2

CALL M,13E2H

If the single precision value in REG 1 is negative then GOSUB to 13E2H to return address of 0982H to the stack pointer.

15C3-15C5

CALL M,0982H

Go convert the negative number in REG 1 to positive if necessary.

15C6-15C8

LD A,(4124H)

Load register A with the exponent of the tangent (which is a single precision value in REG 1).

15C9-15CA

CP 81H

Check to see if the the exponent of the tangent (which is a single precision value in REG 1) is less than one by comparing it against 81H (Binary: 1000 0001). Results:

If A="1" it sets the ZERO FLAG.
If A<"1" then the CARRY FLAG will be set
If A>="1" then the NO CARRY FLAG will be set.

15CB-15CC

JR C,15D9H

Jump to forward to 15D9H if A<"1".

15CD-15CF

LD BC,8100H

Load register pair BC with an exponent and a MSB for a single precision value. This also sets C to 00H.

15D0

LD D,C

Zero the NMSB of the single precision value in register D.

15D1

LD E,C

Zero the LSB of the single precision value in register E.

15D2-15D4

CALL 08A2H

GOSUB 082AH to get the reciprocal of the tangent. This routine divides the single precision value in REG 1 into the single precision constant in register pairs BC and DE.

15D5-15D7

LD HL,0710H

Load register pair HL with a return address of 0710H (which is the subtract routine to be called once the series is calculated).

15D8

PUSH HL

Save the value of the return address in register pair HL to the stack.

15D9-15DB

LD HL,15E3H

Load register pair HL with the starting address for a series of single precision numbers for a set of computations.

15DC-15DE

CALL 149AH

GOSUB to 149AH to do the set of computations.

15DF-15E1

LD HL,158BH

Load register pair HL with the starting address of a single precision constant equal to 1.57079637029 (which is pi/2).

15E2

RET

Return. The return address was set to 0710H above, which will then subtract the last term from pi/2 and then return.

15E3-1607 - SINGLE PRECISION CONSTANTS STORAGE LOCATION

15E3H

09H

The number of single precision constants (9) which follows is stored here

15E4-15E7H

4A D7 3B 78

A single precision constant equal to 0.00286622549 is stored here.

15E8-15EBH

02 6E 84 7B

A single precision constant equal to -0.01616573699 is stored here.

15EC-15EFH

FE C1 2F 7C

A single precision constant equal to 0.04290961441 is stored here.

15F0-15F3H

74 31 9A 3D

A single precision constant equal to 0.07528963666 is stored here.

15F4-15F7H

84 3D 5A 7D

A single precision constant equal to 0.10656264407 is stored here.

15F8-15FBH

C8 7F 91 7E

A single precision constant equal to -0.14208900905 is stored here.

15FC-15FFH

E4 BB 4C 7E

A single precision constant equal to 0.19993549561 is stored here.

1600-1603H

6C AA AA 7F

A single precision constant equal to -0.33333146561 is stored here.

1604-1607H

00 00 00 01

A single precision constant equal to 1.0 is stored here.

1608-18C8 - LIST OF BASIC RESERVED WORDS, TOKENS, AND ENTRY LOCATIONS AS FOLLOWS:

The original ROM source code makes an interesting note about the order of these reserved words. Some reserved words are contained in other reserved words, which will cause a problem. They given examples of:

IF J=F OR T=5 will process a FOR
INP is part of INPUT
IF T OR Q THEN will process a TO

SO, the smaller word always has to appear later in the reserved word table.

Word	Token	Address	Word	Token	Address
ABS	D9	0977	AND	D2	25FD
ASC	F6	2A0F	ATN	E4	15BD
AUTO	B7	2008	CDBL	F1	0ADB
CHR$(	F7	2A1F	CINT	EF	0A7F
CLEAR	B8	1E7A	CLOAD	B9	2C1F
CLOSE	A6	4185	CLS	84	01C9
CMD	85	4173	CONT	B3	1DE4
COS	El	1541	CSAVE	BA	2BF5
CSNG	F0	0ABl	CVD	E8	415E
CVI	E6	4152	CVS	E7	4158
DATA	88	1F05	DEF	DD	415B
DEFDBL	9B	1E09	DEFINT	99	1E03
DEFSNG	9A	1E06	DEFSTR	98	1E00
DELETE	B6	2BC6	DIM	8A	2608
EDIT	9D	2E60	ELSE	95	1F07
END	80	1DAE	EOF	E9	4161
ERL	C2	24DD	ERR	C3	24CF
ERROR	9E	1FF4	EXP	E0	1439
FIELD	A3	417C	FIX	F2	0B26
FN	BE	4155	FOR	81	1CA1
FRE	DA	27D4	GET	A4	4174
GOSUB	91	1EB1	GOTO	5D	1EC2
IF	8F	2039	INKEY$	C9	019D
INP	DB	2AEF	INPUT	89	219A
INSTR	C5	419D	INT	D8	0B37
KILL	AA	4191	LEFT$	F8	2A61
LEN	F3	2A03	LET	8C	1F21
LINE	9C	41A3	LIST	B4	2B2E
LLIST	B5	2B29	LOAD	A7	4188
LOC	EA	4164	LOF	EB	4167
LOG	DF	0809	LPRINT	AF	2067
LSET	AB	4197	MEM	C8	27C9
MERGE	A8	418B	MID$	FA	2A9A
MKD$	EE	4170	NAME	A9	418E
NEW	BB	1B49H	NEXT	87	22B6
NOT	CB	25C4	ON	A1	1FC6
OPEN	A2	4179	OR	D3	25F7
OUT	AO	2AFB	PEEK	E5	2CAA
POINT	C6	0132	POKE	B1	2CB1
POS	DC	27F5	PRINT	B2	206F
PUT	A5	4182	RANDOM	86	01D3
READ	8B	21EF	REM	93	1F07
RESET	82	0138	RESTORE	90	1D91
RESUME	9F	1FAFH	RETURN	92	1EDEH
RIGHT$	F9	2A91	RND	DE	14C9
RSET	AC	419A	RUN	8E	1EA3
SAVE	AD	41A0	SET	83	0135
SGN	D7	098A	SIN	E2	1547
SQR	CD	13E7	STEP	cc	2B01
STOP	94	1DA9	STR$	F4	2836
STRING$	C4	2A2F	SYSTEM	AE	02B2
TAB(	BC	2137	TAN	E3	15A8
THEN	CA		TIME$	C7	4176
TO	BD		TROFF	97	1DF8
TRON	96	1DF8	USING	BF	2CBD
USR	C1	27FE	VAL	FF	2AC5
VARPTR	C0	24EB	+	CD	249F
-	CE	2532	*	CF
/	D0		?	D1
>	D4		=	D5
<	D6		&	26
'	FB	3A93

18C9-18F6 - STORAGE LOCATION FOR LEVEL II BASIC ERROR MESSAGES - "ERRTAB"

18C9

"NF"

NEXT without FOR Error Message (Error 00H)

18CB

"SN"

Syntax Error Error Message (Error 02H)

18CD

"RG"

RETURN without GOSUB Error Message (Error 04H)

18CF

"OD"

Out of DATA) Error Message (Error 06H)

18D1

"FC"

Illegal Function Call Error Message (Error 08H)

18D3

"OV"

Overflow Error Message (Error 0AH)

18D5

"OM"

Out of Memory Error Message (Error 0CH)

18D7

"UL"

Underfined Line Number Error Message (Error 0EH)

18D9

"BS"

Subscript out of Range Error Message (Error 10H)

18DB

"DD"

Redimensioned Array Error Message (Error 12H)

18DD

"/0"

Division by Zero Error Message (Error 14H)

18DF

"ID">

Illegal Direct Operation Error Message (Error 16H)

18E1

"TM"

Type Mismatch Error Message (Error 18H)

18E3

"OS"

Out of String Message (Error 1AH)

18E5

"LS"

Out of Memory Error Message (Error 1CH)

18E7

"ST"

String Too Long Error Message (Error 1EH)

18E9

"CN"

Can't Continue Error Message (Error 20H)

18EB

"NR"

No RESUME Error Message (Error 22H)

18ED

"RW"

RESUME Without Error Error Message (Error 24H)

18EF

"UE"

Unprintable Error Error Message (Error 26H)

18F1

"HO"

Missing Operand Error Message (Error 28H)

18F3

"FD"

Bad file Data Error Message (Error 2AH)

18F5

"L3"

Disk BASIC Command Error Message (Error 2CH)

18F7-1904 - STORAGE LOCATION FOR THE SINGLE PRECISION DIVISION ROUTINE
This code is moved from 18F7-191DH to 4080H-40A5H during non-disk initial setup.

18F7

SUB 00H

Subtract the LSB

18F9

LD L,A

Restore the value to L

18FA

LD A,H

Get the middle byte

18FB

SBC A,00H

Subtract the middle byte

18FD

LD H,A

Move the difference to H

18FE

LD A,B

Get the MSB

18FF

SBC A,00H

Subtract the MSB

1901

LD B,A

Move it back to A

1902

LD A,00H

Clear A

1904

RET

RETurn.

1905-191C - STORAGE LOCATION FOR VALUES PLACED IN RAM UPON INITIALIZATION.

This code is moved to 408E during non-disk initial setup.

1918H

Difference between M1 and M3 ROMs: 1917H - 1918H contains 434CH in the Model I, 444CH in the Model III. This value is loaded to 40A0H (the start of string space pointer) during power-up.

191CH

Difference between M1 and M3 ROMs: 191BH - 191CH contains 42E9H in the Model I, 43E9H in the Model III. This value is loaded to 40A4H (the start of BASIC program pointer) during power-up.

191DH-1935H - MESSAGE STORAGE LOCATION

191D-1923H

"Error"

The Level II BASIC ERROR message is stored here.

1924-1928H

"in"

The Level II BASIC IN message is stored here.

1929-192FH

"READY"

The Level II BASIC READY message is stored here.

1930-1935H

"Break"

The Level II BASIC BREAK message is stored here.

1936-1954 - SCAN STACK ROUTINE

This routine is called with DE as the address of the NEXT index. It scans the stack backwards looking for a FOR push. If one is found, it gets the address of the index and compares with the DE that was in place when this routine was called. If it is equal, then it exits with A=0 and HL=Address of the variable. If it is not equal it will keep scanning until no FOR push is found and then exit with A<>0.

1936-1938

LD HL,0004H

Load register pair HL with 4 so that we can backspace.

1939

ADD HL,SP

Add the 4 (held in HL) to the current value of the stack pointer. HL will hold the current stack pointer, the stack point will bump forward 4.

193A

LD A,(HL)

Load register A with the value held at the current stack point MINUS 4.

193B

INC HL

Bump the value of the memory pointer in register pair HL so as to backspace one more byte in case a FOR token is located.

193C-193D

CP 81H

Check to see if the value in register A (which is the current stack pointer - 4) is a FOR token.

193E

RET NZ

Return if the value in register A isn't a FOR token. This returns with A being non-zero because there was no FOR push.

193F

LD C,(HL)

Load register C with the LSB of the FOR's variable address.

1940

INC HL

Bump the value of the memory pointer in register pair HL so as to backspace the current stack pointer by yet another byte.

1941

LD B,(HL)

Load register B with the MSB of the FOR's variable address.

1942

INC HL

Bump the value of the memory pointer in register pair HL so now HL will be the address of the FOR variable on the stack.

1943

PUSH HL

Save the value in register pair HL (which is the address of the FOR variable) to the stack.

1944

LD L,C

Load register L with the LSB of the FOR variable's address in register C.

1945

LD H,B

Load register H with the MSB of the FOR variable's address in register B.

1946

LD A,D

Load register A with the MSB of the variable address in register D. This sets up fto test the user specified variable address.

1947

OR E

Check to see if the variable address in register pair DE is equal to zero.

1948

EX DE,HL

Exchange the variable address in register pair HL with the variable address in register pair DE so that DE will now hold the address of the FOR variable from the stack.

1949-194A

JR Z,194DH

Skip the next 2 opcodes if the variable address in register pair DE was equal to zero.

194B

EX DE,HL

Exchange the variable address in register pair HL with the variable address in register pair DE so that HL will now have the address of the FOR variable from the stack.

194C

RST 18H

This routine was entered with DE being the address of the NEXT index, so we need to compare that against the index from the stack. To do this, we RST 18 to see if the variable address in HL is the same as in DE, so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

194D-194F

LD BC,000EH

Load register pair BC with the value to backspace to next FOR token (which is 10).

1950

POP HL

Get the memory pointer from the stack of the sign of the increment flag and put it in register pair HL.

1951

RET Z

Return if the FOR block matched the NEXT index block.

1952

ADD HL,BC

If it didn't match, execute that 10 byte stepback in BC for the next possible FOR push.

1953-1954

JR 193AH

Keep looking until the appropriate FOR block has been located.

1955-1962 - DATA MOVEMENT ROUTINE

This routine moves a variable into another area specified by the caller. On entry BC is set as the end address of the list to move (which is the upper limit); DE is set as the start address of the list to move; and HL is the end of the area to move it to.

1955-1957

CALL 196CH

GOSUB to 196CH to make sure there's enough room in memory for the string area.

1958

PUSH BC

Save the end address of the list to move (stored in BC) to the stack.

1959

EX (SP),HL

Save the end address of the list to move (stored in the stack now) to register pair HL.

195A

POP BC

Get the end address of the move from the stack and put it in register pair BC.

195B

RST 18H

Now we need to check to see if the memory pointer in HL is the same as the memory pointer in DE (to see if the move is finished), so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

195C

LD A,(HL)

Get a byte from the source list and put it in register A.

195D

LD (BC),A

Save the byte into wherever BC is pointing.

195E

RET Z

Return if finished with the move (i.e., the memory pointer in register pair HL is the same as the value of the memory pointer in register pair DE).

195F

DEC BC

Decrement the source address (in register pair BC).

1960

DEC HL

Decrement the destination address (in register pair HL).

1961-1962

JR 195BH

Loop until the list was moved.

1963-197D - MEMORY CHECK ROUTINE - Computes the amount of space between HL and the end of memory at FFC6H.

1963

PUSH HL

Save the value in register pair HL to the stack.

1964-1966

LD HL,(40FDH)

Load register pair HL with the starting address of free memory (which is stored at 40FDH).
NOTE: 40FDH-40FEH holds the pointer to the starting address of free memory.

1967-1968

LD B,00H

Load register B with zero.

1969

ADD HL,BC

Add 2 times the number of bytes required to start of free area (held in register pair BC) to the value in register pair HL.

196A

ADD HL,BC

Add the value in register pair BC to the value in register pair HL leaving HL to now contain the end of the free area.

196B-196C

3EH E5H

Z-80 Trick! See the general explanation at 10F8H.

196C

PUSH HL

Save the new free area pointer (which is the start) to the stack.

196D-196E

LD A,C6H

Load register A with C6H (which is the the LSB of FFC6H; the top of memory).

196F

SUB L

Subtract the LSB of the value of the new memory pointer in register L from the value in register A.

1970

LD L,A

Load register L with the adjusted value in register A (i.e., the free memory pointer resulting from subtracting the new starting address).

1971-1972

LD A,FFH

Load register A with the MSB of the top of memory.

1973

SBC A,H

Subtract the MSB of the new memory pointer in register H from the value in register A. If the free space list exceeds FFC6 then the CARRY FLAG gets set, meaning memory overflowed.

1974-1975

JR C,197AH

If the CARRY FLAG is set, display a ?OM ERROR since we are out of memory.

1976

LD H,A

Next we need to determine if the free space list has overflowed the stack area so first we load register H with the adjusted value in register A.

1977

ADD HL,SP

Add the value of the stack pointer to the adjusted value in register pair HL.

1978

POP HL

Get the value from the stack and put it in register pair HL.

1979

RET C

If the CARRY FLAG is set, then we have no overflow - so we better RETURN because the next step is an OM error processor.

197A-197B - OM ERROR entry point.

197A-197B

LD E,0CH

Load register E with the ?OM ERROR.

197C-197D

JR 19A2H

Display an ?OM ERROR message.

197E-1AF7 - LEVEL II BASIC COMMAND MODE

197E-1980

LD HL,(40A2H)

Load register pair HL with the value of the current BASIC line number.
NOTE: 40A2H-40A3H holds the current BASIC line number.

1981

LD A,H

Load register A with the MSB of the current BASIC line number in register H.

1982

AND L

Combine the LSB of the current BASIC line number in register L with the MSB of the current line number in register A.

1983

INC A

Bump the value of the combined BASIC line number in register A. If the current line is FFFFH then we have not started execution of a BASIC program yet (meaning we are still in the inputting phase).

1984-1985

JR Z,198EH

Jump to 198EH if Level II BASIC is still in the command mode (rather than being in execution mode).

1986-1988

LD A,(40F2H)

Load register A with contents of 40F2H.
NOTE: 40F2H holds the error flag.

1989

OR A

Check to see if the error flag is set.

198A-198B

LD E,22H

Load register E with a ?NR ERROR code.

198C-198D

JR NZ,19A2H

Jump to 19A2H if the error flag is set (meaning there was no RESUME address).

198E-1990

JP 1DC1H

Otherwise, jump to 1DC1H (the READY routine) because there was an error in the input phase.

1991-1993

LD HL,(40DAH)

Load register pair HL with the DATA line number (which is stored at 16602).
NOTE: 40DAH-40DBH holds DATA line number.

1994-1996

LD (40A2H),HL

Save the DATA line number in register pair HL.
NOTE: 40A2H-40A3H holds the current BASIC line number.

1997-1998

LD E,02H

Load register E with a ?SN ERROR code.
SN ERROR entry point.

199A-199B

LD E,14H

Load register E with a 14H which is the ?/0 ERROR code.

199C-199E

LD BC,001EH

Load register BC with a ?NF ERROR code.
?NF ERROR entry point.

199F-19A1

LD BC,241EH

Load register BC with a ?RW ERROR code.
?RW ERROR entry point.

19A2-19A4

LD HL,(40A2H)

Load register pair HL with the value of the current BASIC line number which has the error.
NOTE: 40A2H-40A3H holds the current BASIC line number.

19A5-19A7

LD (40EAH),HL

Save the value of the current BASIC line number with the error in register pair HL.
NOTE: 40EAH-40EBH holds the line number with error.

19A8-19AA

LD (40ECH),HL

Save the value of the current BASIC line number with the error in register pair HL.
NOTE: 40ECH-40EDH holds EDIT line number.

19AB-19AD

LD BC,19B4H

Load register pair BC with the return address of 19B4H which is the continuation address after a reinitialization.

19AE-19B0

LD HL,(40E8H)

Load register pair HL with the value of the stack pointer (which is stored at 40E8H).
NOTE: 40E8H-40E9H holds Stack pointer pointer.

19B1-19B3

JP 1B9AH

Jump to 1B9AH to reinitialize the system variables.

19B4

POP BC

Get the value from the stack and put it in register pair BC, which should be 0000H.

19B5

LD A,E

Load register A with the value of the error code in register E.

19B6

LD C,E

Load register C with the value of the error code in register E.

19B7-19B9

LD (409AH),A

Save the value of the error code (from in register A) into 409AH.
NOTE: 409AH holds the RESUME flag.

19BA-19BC

LD HL,(40E6H)

Load register pair HL with the value of the current BASIC program pointer (which is stored in 40E6H) (i.e., the address of the last byte executed in the current line).
NOTE: 40E6H-40E7H holds the temporary storage location.

19BD-19BF

LD (40EEH),HL

Save the value of the current BASIC program pointer (which is stored in 40EEH) in register pair HL.
NOTE: 40EEH-40EFH is used by RESUME.

19C0

EX DE,HL

Load register pair DE with the value of the current BASIC program pointer in register pair HL.

19C1-19C3

LD HL,(40EAH)

Load register pair HL with the value of the last number line executed (which is stored in 16618).
NOTE: 40EAH-40EBH holds the line number with error.

19C4-19C5

LD A,H
AND L

The easiest way to test a 2 Byte Register is to AND the MSB and LSB together, as the only way to get 1111 would be if both the LSB and MSB were 1111. Here, HL las the last line number executed.

19C6

INC A

Bump the value of the combined current BASIC line number. This will test to against FFFFH which would mean we are still in the input phase.

19C7-19C8

JR Z,19D0H

Jump to 19D0H if Level II BASIC is in the command mode (meaning the line number was FFFFH, which then flipped to zero on the prior INC command).

19C9-19CB

LD (40F5H),HL

Save the value of the current BASIC line number in register pair HL to (40F5H).
NOTE: 40F5H-40F6H holds the last line number executed.

19CC

EX DE,HL

Load register pair HL with the value of the current BASIC program pointer in register pair DE.

19CD-19CF

LD (40F7H),HL

Save the value of the current BASIC program pointer (which is stored in 16631) in register pair HL.
NOTE: 40F7H-40F8H holds the last byte executed.

19D0-19D2

LD HL,(40F0H)

Load register pair HL with memory contents held at (40F0H).
NOTE: 40F0H-40F1H holds the ON ERROR adress.

19D3

LD A,H

Load register A with the MSB of the ON ERROR address in register H.

19D4

OR L

Combine the LSB of the ON ERROR address in register L with the MSB of the ON ERROR address in register A.

19D5

EX DE,HL

Load register pair DE with the ON ERROR address in register pair HL.

19D6-19D8

LD HL,40F2H

Load register pair HL with the address of the error flag (which is 40F2H).
NOTE: 40F2H holds the error flag.

19D9-19DA

JR Z,19E3H

Jump to 19E3H (to error out) if there isn't an ON ERROR address.

19DB

AND (HL)

Combine the value of the error flag at the location of the memory pointer in register pair HL with the combined value of the ON ERROR address in register A.

19DC-19DD

JR NZ,19E3H

Jump to 19E3H (to error out) if register A is non zero (meaning that there was no ON ERROR address).

19DE

DEC (HL)

Decrement the value of the error flag at the location of the memory pointer in register pair HL so that RESUME will work.

19DF

EX DE,HL

Load register pair HL with the ON ERROR address in register pair DE.

19E0-19E2

JP 1D36H

Jump to 1D36H to make that happen.

19E3

XOR A

Zero register A.

19E4

LD (HL),A

Clear the error override flag by save a zero (from register A) as the current error flag at the location of the memory pointer in register pair HL..

19E5

LD E,C

Load register E with the value of the error code in register C.

19E6-19E8

CALL 20F9H

We need to position the video to the next line, so go display a carriage return on the video display if necessary.

19E9-19EB

LD HL,18C9H

Load register pair HL with the starting address for the table of error messages.

19EC-19EE

CALL 41A6H

Go to the DOS link at 41A6H (whcih would load and execute BASIC error messages as supplied by DOS).
NOTE: 41A6H-41E4H holds DOS links.
In NEWDOS 2.1, this would be a call to load a DISK BASIC error, with Register E holding the error number.

19EF

LD D,A

Since we are non-DOS, we continue by loading register D with zero.

19F0-19F1

LD A,3FH

Load register A with a "?" (which is ASCII code 3FH).

19F2-19F4

GOSUB to 032AH to display the question mark in register A.

19F5

ADD HL,DE

Add the value of the error code in register pair DE to the starting address of the table of error messages in register pair HL.

19F6

LD A,(HL)

Load register A with the first character of the error message at the location of the table pointer in register pair HL.

19F7-19F9

GOSUB to 032AH to display the first character of the error message in register A.

19FA

RST 10H

Error codes are 2 characters so we need to set the second character of the error in register A, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

19FB-19FD

GOSUB to 032AH to display the second character of the error message in register A.

19FE-1A00

LD HL,191DH

Load register pair HL with 191DH which is the starting address of the READY message.

1A01

PUSH HL

Save the starting address of the READY message (held in HL) to the stack.

1A02-1A04

LD HL,(40EAH)

Load register pair HL with the value of the current BASIC line number (i.e., the statement causing the error).
NOTE: 40EAH-40EBH holds the line number with error.

1A05

EX (SP),HL

Exchange the value of the current BASIC line number in register pair HL with the starting address of the Level II BASIC ERROR message to the stack.

1A06-1A08

CALL 28A7H

We need to display the Level II BASIC ERROR message so we call the WRITE MESSAGE routine at 28A7H.
NOTE:

The routine at 28A7 displays the message pointed to by HL on current system output device (usually video).
The string to be displayed must be terminated by a byte of machine zeros or a carriage return code 0D.
If terminated with a carriage return, control is returned to the caller after taking the DOS exit at 41D0H (JP 5B99H).

1A09

POP HL

Get the value of the BASIC line number with the error from the stack and put it in register pair HL.

1A0A-1A0C

LD DE,FFFEH

Load register pair DE with FFFEH.

This basically reserves the line number 65534 as a trigger for the next few steps.

1A0D

RST 18H

Now we need to compare the BASIC line number causing the error (held in HL) with FFFEH (held in DE) so as to see if we are in the initialization routine, so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

1A0E-1A10

JP Z,0674H

Jump to 0674H if we are in the initialization routine because the error line number was FFFEH.

1A11

LD A,H

We need to see if were in command mode, which is signalled by CURRENT LINE NUMBER of 0. The first step is to load register A with the MSB of the current BASIC line number in register H.

1A12

AND L

Combine the LSB of the current BASIC line number in register L with the MSB of the current BASIC line number in register A.

1A13

INC A

Bump the combined value of the current BASIC line number in register A to test to see if the line number is 00H (meaning command mode).

1A14-1A16

CALL NZ,0FA7H

GOSUB to 0FA7H to display the current BASIC line number in register pair HL if Level II BASIC isn't in the command mode.

1A17H

3E C1

Z-80 Trick! See the general explanation at 10F8H.

1A18

POP BC

Get the value from the stack and put it in register pair BC.

1A19 - "$READY" - Jump to Model II BASIC "READY"
To exit from a machine-language program into BASIC's immediate mode, jump (not call) to $READY.

1A19-1A1BHREADY

CALL 038BH

Go set the current output device to the video display.
Re-entry into BASIC command mode entry point. (see 6CCH also).

1A1C-1A1E

CALL 41ACH

Go call the DOS link at 41ACH.
In NEWDOS 2.1, this is the start of BASIC just before BASIC shows the READY prompt.

1A1F-1A21

CALL 01F8H

Go turn off the cassette recorder.

1A22-1A24

CALL 20F9H

Go display a carriage return if necessary.

1A25-1A27

LD HL,1929H

Load register pair HL with the starting address of the Level II BASIC READY message.

1A28-1A2A

CALL 28A7H

We need to display the Level II BASIC READY message, so we call the WRITE MESSAGE routine at 28A7H.
NOTE:

The routine at 28A7 displays the message pointed to by HL on current system output device (usually video).
The string to be displayed must be terminated by a byte of machine zeros or a carriage return code 0D.
If terminated with a carriage return, control is returned to the caller after taking the DOS exit at 41D0H (JP 5B99H).

1A2B-1A2D

LD A,(409AH)

Load register A with the value of the current error code.
NOTE: 409AH holds the RESUME flag.

1A2E-1A2F

SUB 02H

Check to see if the current error code is a ?SN ERROR code by subtracting 2 from the error code, resulting in a zero if its a SN ERROR and any other number if it isn't..

1A30-1A32

CALL Z,2E53H

GOSUB to 2E53H to the EDIT mode if the current error code is a SN ERROR code.

1A33 - Many routines jump here as the start of the Level II BASIC interpreter.

If the jump here was from an AUTO call, (40E4H) will have the increment number, (40E1H) will be 0 if no AUTO and non-zero if AUTO, and (40E2H) will have the starting line number.

1A33-1A35

LD HL,FFFFH

Load register pair HL with the command mode line number of FFFFH.
NOTE: FFFFH is the command mode line number.

1A36-1A38

LD (40A2H),HL

Save the line number in register pair HL as the current BASIC line number.
NOTE: 40A2H-40A3H holds the current BASIC line number.

1A39-1A3B

LD A,(40E1H)

Load register A with the value of the AUTO flag. It will be zero if not in AUTO, and anything else if in AUTO.

1A3C

OR A

Check to see if in the AUTO mode.

1A3D-1A3E

JR Z,1A76H

Jump to 1A76H if not in the AUTO mode.

1A3F-1A41

LD HL,(40E2H)

We are in AUTO mode so load register pair HL with the current AUTO line number.
NOTE: 40E2H-40E3H holds Current BASIC line number.

1A42

PUSH HL

Save the current AUTO line number (stored in register pair HL) to the stack.

1A43-1A45

CALL 0FAFH

GOSUB to 0FAFH to call the HL TO ASCII routine at 0FAFH (which converts the value in the HL register pair (assumed to be an integer) to ASCII and display it at the current cursor position on the video screen) to display the AUTO line number.

1A46

POP DE

Get the current AUTO line number from the stack and put it in register pair DE.

1A47

PUSH DE

Save the current AUTO line number in register pair DE to the stack.

1A48-1A4A

CALL 1B2CH

Call the SEARCH FOR LINE NUMBER routine at 1B2CH which looks for the line number specified in DE. Returns C/Z with the line found in BC, NC/Z with line number is too large and HL/BC having the next available location, or NC/NZ with line number not found, and BC has the first available one after that.

1A4B-1A4C

LD A,"*"

Load register A with a * (which will be code for a matching line number).

1A4D-1A4E

JR C,1A51H

If the call to 1B2CH shows a matching line number was found in the BASIC program (by returning a C), skip the next instruction so that register A keeps the "*".

1A4F-1A50

LD A,20H

If we are here, then there was no matching line number so we need to change the next character from a "*" (which is loaded into register A which but is not applicable) to a space.

1A51-1A53

Go display the character in register A on the video display (which will be a "*" if a matching line number was found).

1A54-1A56

CALL 0361H

GOSUB to 0361H to get input into the buffer.

1A57

POP DE

Get the current line number from the stack and put it in register pair DE.

1A58-1A59

JR NC,1A60H

Skip the next 3 opcodes if the BREAK key wasn't pressed.

1A5A

XOR A

The BREAK key was pressed so we need to zero register A to clear the AUTO increment flag.

1A5B-1A5D

LD (40E1H),A

Save the value in register A as the current AUTO flag (to turn off AUTO).
NOTE: 40E1H will hold 0 if no AUTO and non-zero if AUTO.

1A5E-1A5F

JR 1A19H

Jump to the normal command mode "READY" routine at 1A19H.

If we are here, then the BREAK key was not pressed.

1A60-1A62

LD HL,(40E4H)

Load register pair HL with the value of the AUTO increment.
NOTE: 40E4H-40E5H holds the AUTO increment number.

1A63

ADD HL,DE

Since we didn't BREAK out of the routine we need to keep processing the AUTO so we add the value of the AUTO line number in register pair DE with the AUTO increment value in register pair HL.

1A64-1A65

JR C,1A5AH

If that addition to the next AUTO line number causes an overflow (by triggering the CARRY FLAG), jump to 1A5AH which is the same as if the BREAK key was hit.

1A66

PUSH DE

Save the current AUTO line number in register pair DE to the stack.

1A67-1A69

LD DE,FFF9H

Load register pair DE with the maximum BASIC line number of FFF9H (=65529).

There is an explanation at 1E5AH as to why 65529 is the highest possible line number (vs 65535 which would make more sense).

1A6A

RST 18H

Now we need to compare the adjusted AUTO line number (in HL) with the maximum BASIC line number (in DE), so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

1A6B

POP DE

Get the current AUTO line number from the stack and put it in register pair DE.

1A6C-1A6D

JR NC,1A5AH

If the adjusted AUTO line number in register pair HL is too large, jump to 1A5AH which is the same as if the BREAK key was hit.

1A6E-1A70

LD (40E2H),HL

Save the adjusted AUTO line number in register pair HL as the current AUTO line number.
NOTE: 40E2H-40E3H holds Current BASIC line number.

1A71-1A72

OR FFH

Load register A with the AUTO flag value.

1A73-1A75

JP 2FEBH

Jump to the EDIT routine to save the current BASIC line.

1A76-1A77

LD A,3EH

Load register A with a > (the prompt that follows READY)

1A78-1A7A

Go display the Level II BASIC prompt in register A on the video display.

1A7B-1A7D

CALL 0361H

GOSUB to 0361H to accept input. HL will hold the buffer address for that input.

1A7E-1A80

JP C,1A33H

Jump to 1A33H if the BREAK key was pressed.

1A81

RST 10H

Since we need to bump the current input buffer pointer in register pair HL until it points to the first character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1A82

INC A

Bump the value of the character in register A. This sets the status flags but saves the CARRY FLAG.

1A83

DEC A

Decrement the value of the character in register A so we can test for an end of statement.

1A84-1A86

JP Z,1A33H

JUMP to 1A33H if we have an end of statement.

1A87

PUSH AF

Save the value in register pair AF to the stack (including the CARRY FLAG).

1A88-1A8A

Call the ASCII TO INTEGER routine at 1E5AH.
NOTE: The routine at 1E5A converts the ASCII string pointed to by HL to an integer deposited into DE. If the routine finds a non-numerica character, the conversion is stopped.

1A8BH - This little looping routine is to clear any trailing blanks between the line number and the statement.

1A8B

DEC HL

Decrement the value of the input buffer pointer in register pair HL.

1A8C

LD A,(HL)

Load register A with the value of the character at the location of the input buffer pointer in register pair HL.

1A8D-1A8E

CP 20H

Check to see if the character at the location of the input buffer pointer in register A is a space.

1A8F-1A90

JR Z,1A8BH

Loop back to 1A8BH if the character at the location of the input buffer pointer in register A is a space.

1A91

INC HL

Bump the value of the input buffer pointer in register pair HL so that it points to the first character following a line number.

1A92

LD A,(HL)

Load register A with that character.

1A93-1A94

CP 20H

Check to see if the character at the location of the input buffer pointer in register A is a space.

1A95-1A97

CALL Z,09C9H

If it is a space then skip it by a GOSUB to 09C9H which bumps the value of the input buffer pointer in register pair HL if necessary.

1A98

PUSH DE

Save the BASIC line number in register pair DE (which was converted from ASCII to an integer in 1A88H through a call to 1E5AH) to the stack.

1A99-1A9B

CALL 1BC0H

Tokenize the input via a GOSUB to 1BC0H. BC will equal the length of the encoded statement when its done.

1A9C

POP DE

Get the value of the BASIC line number (which is an integer) from the stack.

1A9D

POP AF

Get the CARRY FLAG (from the 1A81H character fetch) and put it in register pair AF.

1A9E-1AA0

LD (40E6H),HL

Save the input buffer pointer in register pair HL.
NOTE: 40E6H-40E7H holds the temporary storage location.

1AA1-1AA3

CALL 41B2H

Go call the DOS line at 4182H.
In NEWDOS 2.1, this is the input scanner after tokenizing the current statement.

1AA4-1AA6

JP NC,1D5AH

Jump to 1D5AH if there wasn't a line number with the input (meaning it was a direct statement or a system command).

1AA7

PUSH DE

Save the BASIC line number (as an integer stored in register pair DE) to the stack.

1AA8

PUSH BC

Save the length of the tokenized input (stored in register pair BC) to the stack.

1AA9

XOR A

Zero register A.

1AAA-1AAC

LD (40DDH),A

Save the value in register A (which is a 00H) as the input flag.
NOTE: 40DDH holds INPUT flag.

1AAD

RST 10H

Since we need find the first token, we have to bump the current input buffer pointer in register pair HL until it points to the next character by calling the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1AAE

OR A

Set the flags.

1AAF

PUSH AF

Save the status flag to the stack.

1AB0

EX DE,HL

Load register pair HL with the integer value of the BASIC line number (held in register pair DE).

1AB1-1AB3

LD (40ECH),HL

Save the integer value of the line number (held in register pair HL) to 40ECH.
NOTE: 40ECH-40EDH holds EDIT line number.

1AB4

EX DE,HL

Exchange the value of the input buffer pointer in register pair DE with the integer value of the BASIC line number in register pair HL. This will fill DE with the line number for the search routine in the next instruction.

1AB5-1AB7

CALL 1B2CH

1AB8

PUSH BC

Save the address of the line number in the BASIC program (if it exists) in register pair BC to the stack.

1AB9-1ABB

CALL C,2BE4H

If there wasn't a matching line number in the BASIC program, GOSUB to 2BE4H to move the closest line number up in memory to make room for another line.

1ABC

POP DE

Get the integer address of the BASIC line number from the stack and put it in register pair DE.

1ABD

POP AF

Restore the status from the 1AADH token scan into register pair AF.

1ABE

PUSH DE

Save the integer address of the BASIC line number to the stack.

1ABF-1AC0

JR Z,1AE8H

Jump to 1AE8H if there was a matching line number in the BASIC program; otherwise we move on and a new line has to be added as follows.

1AC1

POP DE

Get the address of the BASIC line number from the stack and put it in register pair DE.

1AC2-1AC4

LD HL,(40F9H)

Load register pair HL with the end of the BASIC program pointer.

Note: 40F9H-40FAH holds the starting address of the simple variable storage area.

1AC5

EX (SP),HL

Exchange the length of the tokenized input to the stack with the end of the BASIC program pointer in register pair HL.

1AC6

POP BC

Get the end of the BASIC program pointer from the stack and put it in register pair BC.

1AC7

ADD HL,BC

Add the end of the BASIC program pointer in register pair BC to the value of the length of the tokenized input in register pair HL.

1AC8

PUSH HL

Save the adjusted end of the BASIC program pointer in register pair HL to the stack.

1AC9-1ACB

CALL 1955H

Go check to see if there is enough room in memory for the new BASIC line by GOSUB to 1955H.

1ACC

POP HL

Get the new end of the BASIC program pointer from the stack and put it in register pair HL.

1ACD-1ACF

LD (40F9H),HL

Save the new end of the BASIC program pointer in register pair HL.

Note: 40F9H-40FAH holds the starting address of the simple variable storage area.

1AD0

EX DE,HL

Load register pair HL with the address of the BASIC line.

1AD1

LD (HL),H

Save the MSB of the address of the BASIC line in register H.

1AD2

POP DE

Get the value of the BASIC line number from the stack and put it in register pair DE.

1AD3

PUSH HL

Save the value of the memory pointer in register pair HL to the stack.

1AD4

INC HL

Bump the value of the memory pointer in register pair HL (which bumps it to the LSB of the line number entry).

1AD5

INC HL

Bump the value of the memory pointer in register pair HL (which bumps it to the MSB of the line number entry).

1AD6

LD (HL),E

Save the LSB of the BASIC line number in register E at the location of the memory pointer in register pair HL.

1AD7

INC HL

Bump the value of the memory pointer in register pair HL.

1AD8

LD (HL),D

Save the MSB of the BASIC line number in register D at the location of the memory pointer in register pair HL. At this point DE should have the binary value for the new line number.

1AD9

INC HL

Bump the value of the BASIC line number in register pair HL.

1ADA

EX DE,HL

Load register pair DE with first data byte address following the line number (held in register pair HL).

1ADB-1ADD

LD HL,(40A7H)

Load register pair HL with the value of the tokenized input pointer
Note: 40A7H-40A8H holds Input Buffer pointer.

1ADE

EX DE,HL

Exchange the value of the memory pointer in register pair DE with the value of the tokenized input pointer in register pair HL.

1ADF

DEC DE

Decrement the value of the tokenized input buffer pointer in register pair DE.

1AE0

DEC DE

Decrement the value of the tokenized input buffer pointer in register pair DE.

1AE1

LD A,(DE)

Load register A with the value at the location of the tokenized input buffer pointer in register pair DE.

1AE2

LD (HL),A

Save the value in register A at the location of the memory pointer in register pair HL.

1AE3

INC HL

Bump the store address (held in register pair HL).

1AE4

INC DE

Bump the fetch address (held in register pair DE).

1AE5

OR A

Check to see if the character in register A is an end of the line character.

1AE6-1AE7

JR NZ,1AE1H

Loop until the whole of the new BASIC line has been stored in memory.

1AE8

POP DE

Get the address of the line in the program table from the stack and put it in register pair DE.

1AE9-1AEB

CALL 1AFCH

Go update line pointers for all lines following the new line.

1AEC-1AEE

CALL 41B5H

Go call the DOS link at 41B5H.
In NEWDOS 2.1, this is the input scanner after updating the PST (Program Statement Table).

1AEF-1AF1

CALL 1B5DH

Update all the BASIC line pointers.

1AF2-1AF4

CALL 41B8H

Go call the DOS link at 41B8H.
In NEWDOS 2.1, this is the input scanner after reinitializing BASIC

1AF5-1AF7

JP 1A33H

Go get the input again.

1AF8-1B0F - LINE POINTERS ROUTINE

This routine fixes the line pointers in a BASIC program. This is useful, for instance for a renumber program which has to move BASIC program lines from one location in memory to an other, which means that the line pointers would no longer be valid. This routine will fix them. Registers A, HL and DE are used.

1AF8

LD HL,(40A4H)

Load register pair HL with the start of the BASIC program pointer (called the PST).
NOTE: 40A4H-40A5H holds the starting address of BASIC program text also known as the PROGRAM STATEMENT TABLE (PST).

1AFB

EX DE,HL

Move the PST address to DE.

1AFC

LD H,D

Load register H with the MSB of the memory pointer in register D.

1AFD

LD L,E

Load register L with the LSB of the memory pointer in register E.

1AFE

LD A,(HL)

Load register A with the value at the location of the memory pointer in register pair HL.

1AFF

INC HL

Bump the value of the memory pointer in register pair HL.

1B00

OR (HL)

Since the first 2 bytes of each line contains the address of the next line, a 0000H would signify the end byte. With this, check to see if the character at the location of the memory pointer in register pair HL is an end of the BASIC program character.

1B01

RET Z

Return if done.

1B02

INC HL

Since HL is the 'beginning of statment pointer', we need to skip over the 3rd and 4th bytes, so bump the value of the memory pointer in register pair HL.

1B03

INC HL

Bump the value of the memory pointer in register pair HL.

1B04

INC HL

Bump the value of the memory pointer in register pair HL.

1B05

XOR A

Zero register A and clear the flags.

1B06

CP (HL)

Check to see if the character at the location of the memory pointer in register HL is an end of the BASIC line character.

1B07

INC HL

Bump the value of the memory pointer in register pair HL.

1B08

JR NZ,1B06H

Loop until the end of the BASIC line character is found.

1B0A

EX DE,HL

Exchange the starting address of the current BASIC line in register pair DE with the starting address of the next BASIC line in register pair HL.

1B0B

LD (HL),E

Save the LSB of the next BASIC line's starting address in register E at the location of the memory pointer in register pair HL.

1B0C

INC HL

Bump the value of the memory pointer in register pair HL.

1B0D

LD (HL),D

Save the MSB of the next BASIC line's starting address in register D at the location of the memory pointer in register pair HL.

1B0E-1B0F

JR 1AFCH

Loop until the end of the program has been found.

1B10-1B48 - EVALUATE LINE NUMBERS

This is called by LIST and DELETE. It converts the starting and ending linbers (X-Y) to binary and saves the ending line number on the stack. Then the code locates the program table address for the starting line. The routine leaves the address of the starting line in BC and the ending line number in the stack.

1B10-1B12

LD DE,0000H

Load register pair DE (which will be the line counter) with zero.

1B13

PUSH DE

Save the value in register pair DE to the stack.

1B14-1B15

JR Z,1B1FH

Jump to 1B1FH if there aren't any line numbers to be evaluated.

1B16

POP DE

Get the value from the stack and put it in register pair DE (which will be the line number).

1B17-1B19

CALL 1E4FH

Go evaluate the line number at the location of the current BASIC program pointer in register pair HL and return with the line number's binary value in register pair DE.

1B1A

PUSH DE

Save the first line number's value (stored in register pair DE) to the stack.

1B1B-1B1C

JR Z,1B28H

Jump if there isn't a second line number to be evaluated given (i.e, LIST 3000-).

1B1D-1B1E

RST 08H ⇒ CEH

If we are here, there is a second line number. That that would have to be preceded by a - at the location of the current BASIC program pointer in register pair HL, call the COMPARE SYMBOL routine which comparess the symbol in the input string pointed to by HL register to the value in the location following the RST 08 call. If there is a match, control is returned to address of the RST 08 instruction 2 with the next symbol in the Aregister and HL incremented by one. If the two characters do not match, a syntax error message is given and control returns to the Input Phase).

1B1F-1B21

LD DE,FFFAH

Load register pair DE with the default second line number of FFAFH.

1B22-1B24

CALL NZ,1E4FH

Go evaluate the second line number at the location of the current BASIC program pointer in register pair HL and return with the line number's binary value in register pair DE. Will return with Z flag set if it was a number.

1B25-1B27

JP NZ,1997H

Go to the Level II BASIC error routine and display a SN ERROR message if the data which followed the token wasn't a line number.

1B28

EX DE,HL

Load register pair HL with the value of the second line number in register pair DE and load register pair DE with the value of the current BASIC program pointer in register pair HL.

1B29

POP DE

Get the value of the first line number from the stack and put it in register pair DE.

1B2A

EX (SP),HL

Exchange the return address to the stack with the value of the second line number in register pair HL.

1B2B

PUSH HL

Save the value of the return address in register pair HL to the stack so we can properly exit later.

1B2C - This routine searches a BASIC program for a BASIC line with a line number matching the value in the DE register pair.

To use this routine, the required line number must be placed in the DE register pair. When a match is found, this routine sets the CARRY FLAG; the BC register pair points to the start of the required line, and the HL register points to the start of the next line. HL, AF and BC are used.

This is the the SEARCH FOR LINE NUMBER routine at 1B2C, which searches the Program Statement Table (PST) for a BASIC statement with the line number specified in the DE register pair. All registers are used. The exit conditions are:

C/Z=Line Found and BC is the starting address of the line in the PST and HL is the address following;

NC/Z=Line not found or too large and HL/BC will have the address of the next available PST location; and

NC/NZ=Line not found and BC=Address of the first line number greater than the one specified and HL will be the address of the following line.

1B2C

LD HL,(40A4H)

Load register pair HL with the value of the start of the BASIC program pointer.
Note: 40A4H-40A5H holds the starting address of BASIC program text also known as the PROGRAM STATEMENT TABLE (PST).

1B2F

LD B,H

Load register B with the value of the MSB of the memory pointer in register H.

1B30

LD C,L

Load register C with the LSB of the memory pointer in register L. Now BC will hold the address of the current line in the PST.

1B31

LD A,(HL)

Load register A with the LSB of the address of the next line (held in register pair HL).

1B32

INC HL

Bump the value of the memory pointer in register pair HL to the MSB of the address of the next line.

1B33

OR (HL)

Combine the value at the location of the memory pointer in register pair HL with the value in register A and set the status flags.

1B34

DEC HL

Restore HL to the start of the current line.

1B35

RET Z

Return if this is the end of PST (=the end of the BASIC program).

1B36

INC HL

It's not the end so we need HL to point the line number for the current line which means it must advance by 2. Bump the value of the memory pointer in register pair HL.

1B37

INC HL

Bump the value of the memory pointer in register pair HL.

1B38

LD A,(HL)

Load register A with the LSB of the current BASIC line number at the location of the memory pointer in register pair HL.

1B39

INC HL

Bump the value of the memory pointer in register pair HL to point to the MSB of the current BASIC line number.

1B3A

LD H,(HL)

Load register H with the MSB of the current BASIC line number at the location of the memory pointer in register pair HL.

1B3B

LD L,A

Load register L with the LSB of the current BASIC line number in register A.

1B3C

RST 18H

Now we need to compare the value of the current BASIC line number in HL and the first line number (in DE), so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

1B3D

LD H,B

Load register H with the MSB of the memory pointer in register B.

1B3E

LD L,C

Load register L with the LSB of the memory pointer in register C.

1B3F

LD A,(HL)

Load register A with the value at the location of the memory pointer in register pair HL.

1B40

INC HL

Bump the value of the memory pointer in register pair HL.

1B41

LD H,(HL)

Load register H with the MSB of the next BASIC line pointer at the location of the memory pointer in register pair HL.

1B42

LD L,A

Load register L with the LSB of the next BASIC line pointer in register A to form the address of the next line in HL.

1B43

CCF

Complement the value of the CARRY FLAG. The carry will be set if the current line number is < the value in DE. This will clear the CARRY FLAG.

1B44

RET Z

Return if the first line number in register pair DE is the same as the current BASIC line number. The line numbers match, so exit C, Z, BC=address of the current line, and HL=address of the next line.

If we are here, then we have no match.

1B45

CCF

Complement (reverse) the CARRY FLAG.

1B46

RET NC

If the first line number in register pair DE is less than the current BASIC line number. BC will be the address of the current line and HL will be the address of the next line.

1B47

JR 1B2FH

Loop until the location of the line number has been found in the BASIC program.

1B49-1B5C - LEVEL II BASIC NEW ROUTINE

1B49

RET NZ

Go to the Level II BASIC error routine and display a ?SN ERROR message if there is any input following the NEW token.

1B4A-1B4C

CALL 01C9H

Call the CLEAR SCREEN routine at 01C9 (which cleans the screen, changes to 64 characters, and homes the screen).

1B4D

LD HL,(40A4H)

Load register pair HL with the start of the PST (the start of the BASIC program).

Note: 40A4H-40A5H holds the starting address of BASIC program text also known as the PROGRAM STATEMENT TABLE (PST).

1B50

CALL 1DF8H

GOSUB to the TROFF routine at 1DF8H (which just loads A with a zero for TROFF, and puts that 0 into 411BH).

1B53

LD (40E1H),A

Reset the AUTO flag by putting a zero (which is in A due to the GOSUB to the TROFF statement in the above instruction) into 40E1H.

1B56

LD (HL),A

We need to initialize the PST, and the way to do that is to zero the first two bytes so ... save a zero at the location of the memory pointer in register pair HL.

1B57

INC HL

... bump the value of the memory pointer in register pair HL ...

1B58

LD (HL),A

... and save a zero at the location of the memory pointer in register pair HL.

1B59

INC HL

Bump the value of the memory pointer in register pair HL.

1B5A

LD (40F9H),HL

Save the value in register pair HL at 40F9H to initialize the start of the variable list table as the end of the PST.

Note: 40F9H-40FAH holds the starting address of the simple variable storage area.

1B5D-1BB2 - LEVEL II BASIC RUN ROUTINE

Differences between M1 and M3 ROMs: The locations 1B5DH - 1B5FH are part of the RUN, NEW, EDIT, etc. commands; in the Model I these three bytes contain a LD HL,(40A4H) instruction (resets HL to point to the start of the BASIC program). In the Model III, this has been replaced by a CALL 046BH instruction, which unprotects the video display in addition to resetting HL to the start of the BASIC program.

This routine does a lot of variable resets and other things that are common to NEW as well, so NEW just does the special NEW stuff and than passes right through to here to reset the rest.
To use a ROM call to RUN a BASIC program, starting with its first line, execute the following instructions:
LD HL,1D1EH
PUSH HL
JP 1B5DH
The ability to RUN a BASIC program from an assembly language program is valuable for linking the two programs.

*1B5D-1B5F

CALL 046BH

GOSUB to 046BH to unprotect the screen and point HL to the start of data.

1B60

DEC HL

Decrement the value in register pair HL to backspace.

1B61-1B63

LD (40DFH),HL

Save the adjusted value in register pair HL into 40DFH.
NOTE: 40DFH-40E0H is used by DOS.

1B64-1B65

LD B,1AH

Load register B with the number of variable names to be initialized (which is 26).

1B66-1B68

LD HL,4101H

Load register pair HL with the starting address of the variable declaration table (which is 4101H).
NOTE: 4101H-411AH holds Variable Declaration Table.

1B69-1B6A

LD (HL),04H

Set the variable at the location of the memory pointer in register pair HL to a single precision variable.

1B6B

INC HL

Bump the value of the memory pointer in register pair HL to the next variable.

1B6C-1B6D

DJNZ 1B69H

Loop until all 26 variables have been set to single precision.

1B6E

XOR A

Zero register A.

1B6F-1B71

LD (40F2H),A

Save the value in register A (which is a zero) as the current value of the RESUME flag to say that there is no error for RESUME to handle.
NOTE: 40F2H holds the error flag.

1B72

LD L,A

Zero register L.

1B73

LD H,A

Zero register H.

1B74-1B76

LD (40F0H),HL

Save a zero (held in register pair HL) as the current ON ERROR address.
NOTE: 40F0H-40F1H is used by ON ERROR.

1B77-1B79

LD (40F7H),HL

Save a zero (held in register pair HL) as the current BREAK, STOP, or END address.
NOTE: 40F7H-40F8H holds the last byte executed.

1B7A-1B7C

LD HL,(40B1H)

Load register pair HL with the top of the memory pointer held in 40B1H.
NOTE: 40B1H-40B2H holds MEMORY SIZE? pointer.

1B7D-1B7F

LD (40D6H),HL

Save the top of memory pointer (held in register pair HL) as the next available address in the string space pointer.
NOTE: 40D6H-40D7H holds Next available location in string space pointer.

1B80-1B82

CALL 1D91H

Go do a RESTORE (which will mess with DE and HL).

1B83-1B85

LD HL,(40F9H)

Load register pair HL with the end of the BASIC program pointer.

Note: 40F9H-40FAH holds the starting address of the simple variable storage area.

1B86-1B88

LD (40FBH),HL

Save the value in register pair HL as the new simple variables pointer.

Note: 40FBH-40FCH holds the starting address of the BASIC array variable storage area.

1B89-1B8B

LD (40FDH),HL

Save the value in register pair HL as the new array variables pointer.
NOTE: 40FDH-40FEH holds the pointer to the starting address of free memory.

1B8C-1B8E
CALL 41BBH
Go call the DOS line at 41BBH.
In NEWDOS 2.1 this initializes BASIC for a new routine.
1B8FH - Inside the RUN routine - Initialize the Level II BASIC variables and pointers

1B8F

POP BC

Get the return address from the stack because we are about to change the stack pointer.

1B90-1B92

LD HL,(40A0H)

Load register pair HL with the start of string space pointer.
Note: 40A0H-40A1H holds the start of string space pointer.

1B93

DEC HL

Decrement the value of the memory pointer in register pair HL.

1B94

DEC HL

Decrement the value of the memory pointer in register pair HL (so now HL has the sart of the string space pointer - 2).

1B95-1B97

LD (40E8H),HL

Save the string space pointer - 2 (in register pair HL) as the stack pointer
Note: 40E8H-40E9H holds Stack pointer pointer.

1B98

INC HL

Bump the value of the memory pointer in register pair HL.

1B99

INC HL

Bump the value of the memory pointer in register pair HL so it is back to being the start of the string space pointer.

1B9A

LD SP,HL

Load the stack pointer with the start of the string space pointer (held in register pair HL).

1B9B-1B9D

LD HL,40B5H

Load register pair HL with the start of the string work area (which is 40B5H).
NOTE: 40B5H-40D2H holds Temporary string work area.

1B9E-1BA0

LD (40B3H),HL

Save the value in register pair HL as the next available location in the string work area pointer.
NOTE: 40B3H-40B4H holds Next available location in the temporary string work area pointer.

1BA1-1BA3

CALL 038BH

GOSUB 038BH to set the current output device to the video display.

1BA4-1BA6

CALL 2169H

Go turn off the cassette recorder.

1BA7

XOR A

Zero register A.

1BA8

LD H,A

Zero register H.

1BA9

LD L,A

Zero register L.

1BAA-1BAC

LD (40DCH),A

Clear the FOR statement flag.
NOTE: 40DCH holds FOR flag.

1BAD

PUSH HL

Save the value in register pair HL (which is RUN) to the stack.

1BAE

PUSH BC

Save the value in register pair BC (which is the address to continue executing code) to the stack.

1BAF-1BB1

LD HL,(40DFH)

Load register pair HL with the current value of the BASIC program pointer.
NOTE: 40DFH-40E0H holds Used by DOS.

1BB2

RET

Return.

1BB3-1BBF - KEYBOARD INPUT ROUTINE

This is the last of the general purpose input routines. This routine functions identically to the 361H routine with the exception that it prints a "?" on the screen (like INPUT does with BASIC) before allowing input from the keyboard.

To use a ROM call to display "?" on the video screen at the current cursor position (Non-DOS Systems Only), and then to input a string of up to 240 characters, execute CALL 1BB3H. The input string will be in consecutive memory locations starting at the address contained in 40A7H-40A8H, with a zero byte at the end. The HL register pair will contain an address one less than the starting address of the stored input.

1BB3-1BB4HINPUT

LD A,3FH

Load register A with a ?.

1BB5-1BB7

Go display the ? (stored in register A) on the video display.

1BB8-1BB9

LD A,20H

Load register A with a space.

1BBA-1BBC

Go display the space in register A on the video display.

1BBD-1BBF

JP 0361H

Jump to the keyboard input routine at 0361H.

1BC0-1C8F - TOKENIZE INPUT ROUTINE

1BC0

XOR A

Zero register A.

1BC1-1BC3

LD (40B0H),A

Save the value in register A as the current value of the tokenization flag.
NOTE: 40B0H holds the temporary storage location.

1BC1-1BC3

LD (409FH),A

Save the value in register A into the DATA FLAG held in 409FH.
NOTE: Bit 0 HIGH means inside a quote. Bit 1 HIGH means inside a DATA. Bit 2 HIGH means inside a REM.
NOTE: In the original Model III ROM, this byte was placed into 40B0H which was just a temporary storage location.

1BC4

LD C,A

Zero register C.

1BC5

EX DE,HL

Load register pair DE with the address of the first character after the line number (as stored in register pair HL).

1BC6-1BC8

LD HL,(40A7H)

Load register pair HL with the starting address of the input buffer.
NOTE: 40A7H-40A8H holds Input Buffer pointer.

1BC9

DEC HL

We need to backspace twice so ... decrement the value of the input buffer pointer in register pair HL.

1BCA

DEC HL

... and again decrement the value of the input buffer pointer in register pair HL.

1BCB

EX DE,HL

Exchange the string address - 2 from HL into DE, and the current input string address from DE into HL.

1BCC

LD A,(HL)

Load register A with the character at the current input string address (in register pair HL).

1BCD-1BCE

CP 20H

Check to see if the character in register A is a space.

1BCF-1BD1

JP Z,1C5BH

Jump to 1C5BH if the character in register A is a .

1BD2

LD B,A

Load register B with the value of the character in register A.

1BD3-1BD4

CP 22H

Check to see if the character in register A is a ".

1BD5-1BD7

JP Z,1C77H

Jump to 1C77H if the character in register A is a ". 1C77H will move the entire field between the quotes into the a code string.

1BD8

OR A

Check to see if the character in register A is an end of the input character and set the status flags.

1BD9-1BDB

JP Z,1C7DH

Jump to 1C7DH if the character in register A is an end of the input character.

1BDC-1BDE

LD A,(40B0H)

Load register A with the value of the tokenization flag for DATA.
NOTE: 40B0H holds the temporary storage location.

1BDC-1BDE

LD A,(409FH)

Load register A with the value of the DATA FLAG.
NOTE: Bit 0 HIGH means inside a quote. Bit 1 HIGH means inside a DATA. Bit 2 HIGH means inside a REM.
NOTE: In the original Model III ROM, this byte was read from 40B0H which was just a temporary storage location.

1BDF

OR A

Check to see if a DATA statement is being processed.

1BE0

LD A,(HL)

Load register A with the value of the next character.

1BE1-1BE3

JP NZ,1C5BH

Jump to 1C5BH if a DATA statement is being processed.

1BE4-1BE5

CP 3FH

Check to see if the character in register A is a ? (meaning a PRINT statement).

1BE6-1BE7

LD A,B2H

Load register A with a PRINT token of B2H.

1BE8-1BEA

JP Z,1C5BH

Jump to 1C5BH if the character at the location of the input buffer pointer in register pair HL is a ?. This will replace the ? with PRINT.

1BEB

LD A,(HL)

Re-fetch the current character (from the memory location of the input buffer pointer in register pair HL) and put it into Register A.

1BEC-1BED

CP 30H

Check to see if the character in register A is less than a zero character (alpha numeric).
NOTE: Results from a CP:

Z: A and * are the same
NZ: A and * are NOT the same
C: A < *
NC: A => *

1BEE-1BEF

JR C,1BF5H

Jump to 1BF5H if the character in register A is less than a zero character, meaning it is not a digit or letter.

1BF0-1BF1

CP 3CH

Check to see if the character in register A is less than < character (which is a test to see if it is 0-9, :, ;, <, constant or special character.
NOTE: Results from a CP:

Z: A and * are the same
NZ: A and * are NOT the same
C: A < *
NC: A => *

1BF2-1BF4

JP C,1C5BH

Jump to 1C5BH if the character in register A is 0-9, :, ;, <, constant or special character.

1BF5

PUSH DE

Save the value of the input buffer pointer in register pair DE to the stack.

1BF6-1BF8

LD DE,164FH

Load register pair DE with the starting address of the reserved words list.

1BF9

PUSH BC

Save the value in Register Pair BC to the STACK.

1BFA-1BFC

LD BC,1C3DH

Load register pair BC with the return address after matching the reserved word list.

1BFD

PUSH BC

Save the return address in register pair BC to the stack .

1BFE-1BFF

LD B,7FH

Load register B with the initial reserved words counter.

1C00

LD A,(HL)

Load register A with the character at the location of the input buffer pointer in register pair HL.

1C01-1C02

CP 61H

Check to see if the character in register A is lower?case.
NOTE: Results from a CP:

Z: A and * are the same
NZ: A and * are NOT the same
C: A < *
NC: A => *

1C03-1C04

JR C,1C0CH

Jump to 1C0CH if the character in register A isn't lowercase.

1C05-1C06

CP 7BH

Check to see if the character in register A is lower?case.

1C07-1C08

JR NC,1C0CH

Jump down 2 instructions to 1C0CH if the character in register A isn't lowercase.

1C09-1C0A

AND 5FH

Make the lowercase character in register A upper?case.

1C0B

LD (HL),A

Save the adjusted character in register A at the location of the input buffer pointer in register pair HL.

1C0C

LD C,(HL)

Load register C with the character at the location of the input buffer pointer in register pair HL.

1C0D

EX DE,HL

Exchange the input buffer pointer in register pair HL with the reserved words list pointer in register pair DE.

1C0E

INC HL

Bump the value of the reserved words list pointer to the next reserved word and put that in register pair HL.

1C0F

OR (HL)

Check to see if bit 7 of the character at the location of the reserved words list pointer in register pair HL is set.

1C10-1C12

JP P,1C0EH

Jump to 1C0EH if the character at the location of the reserved words list pointer in register pair HL doesn't have bit 7 set.

1C13

INC B

Bump the value of the reserved words counter in register B.

1C14

LD A,(HL)

Load register A with the character at the location of the reserved words list pointer in register pair HL.

1C15-1C16

AND 7FH

Reset bit 7 (the sign bit) of the character in register A.

1C17

RET Z

Return if this is the end of the reserved words list.

1C18

CP C

Check to see if the character in register C is the same as the character at the location of the reserved words list pointer in register A.

1C19-1C1A

JR NZ,1C0EH

Jump to 1C0EH if the characters don't match.

1C1B

EX DE,HL

Exchange the value of the reserved words list pointer in register pair HL with the value of the input buffer pointer in register pair DE.

1C1C

PUSH HL

Save the starting address of the current symbol (stored register pair HL) to the stack.

1C1D

INC DE

Bump the value of the reserved words list pointer in register pair DE.

1C1E

LD A,(DE)

Load register A with the character at the location of the reserved words list pointer in register pair DE.

1C1F

OR A

Check to see if bit 7 of the character in register A is set.

1C20-1C22

JP M,1C39H

Jump to 1C39H if we have the control element (i.e., bit 7 of the character in register A is set).

1C23

LD C,A

Load register C with the character in register A.

1C24

LD A,B

Load register A with the value of the reserved words counter in register B.

1C25-1C26

CP 8DH

Check to see if the current reserved word being checked is GOTO.

1C27-1C28

JR NZ,1C2BH

Jump to 1C2BH if the current reserved word being checked isn't GOTO.

1C29

RST 10H

Since we need to skip spaces we need to bump the current input buffer pointer in register pair HL until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1C2A

DEC HL

Decrement the value of the input buffer pointer in register pair HL.

1C2B

INC HL

Bump the value of the input buffer pointer in register pair HL to point to the next character.

1C2C

LD A,(HL)

Load register A with the next element from the string input (i.e., the character at the location of the input buffer pointer in register pair HL).

1C2D-1C2E

CP 61H

Check to see if the character in register A is lower-case. Results:

If A=61H it sets the ZERO FLAG
If A<61H then the CARRY FLAG will be set
if A>=61H then the NO CARRY FLAG will be set.

If A is a not lower case then C will be set.

1C2F-1C30

JR C,1C33H

Jump to 1C33H if the character in register A isn't lowercase.

1C31-1C32

AND 5FH

Mask A against 5FH (Binary: 0101 1111) to turn off bits 5 and 7 (which locks A to be between 00H and 7FH).

1C33

CP C

Check to see if the character in register A (the input element) matches the character in register C (the syntax element).

1C34-1C35

JR Z,1C1DH

Jump back to 1C1DH if the character in the input matches the reserved words character.

1C36

POP HL

If we didn't just jump away, we need to restart the scan from the last point in the syntax list (which is stored in the stack) and put it into HL.

1C37-1C38

JR 1C0CH

Jump back to 1C0CH.

1C39

LD C,B

Load register C with the value of the reserved words counter in register B.

1C3A

POP AF

Get the value from the stack and put it in register pair AF (which is just disposing of the HL push from 1C1CH).

1C3B

EX DE,HL

Exchange the current string with the syntax tree address for the string.

1C3C

RET

Return.

1C3D

EX DE,HL

Exchange the reserved words list pointer in register pair HL with the input buffer pointer in register pair DE.

1C3E

LD A,C

Load register A with the value of the reserved words counter in register C.

1C3F

POP BC

Get the value from the stack and put it in register pair BC (basically to clear the return address from the stack).

1C40

POP DE

Get the input buffer pointer -2 from the stack and put it in register pair DE.

1C41

EX DE,HL

Exchange the input buffer pointer in register pair HL with the input buffer pointer in register pair DE. HL will be the buffer origin - 2 and DE will be the current string address.

1C42-1C43

CP 95H

Check to see if the token in register A is an ELSE token.

1C44-1C45

LD (HL),3AH

Save a colon at the location of the input buffer pointer -2 in register pair HL.

1C46-1C47

JR NZ,1C4AH

Jump to 1C4AH if the token in register A isn't an ELSE token.

1C48

INC C

Bump the value of the counter in register C (which is tracking the token buffer).

1C49

INC HL

Bump the value of the input buffer pointer in register pair HL (which is the token buffer).

1C4A-1C4B

CP 0FBH

Check to see if the token in register A is a REM token.

1C4C-1C4D

JR NZ,1C5AH

Jump to 1C5AH if the token in register A isn't a REM token.

1C4E-1C4F

LD (HL),3AH

Save a ":" at the memory location of the input buffer pointer in register pair HL.

1C50

INC HL

Bump the value of the input buffer pointer in register pair HL (because we just inserted a :).

1C51-1C52

LD B,93H

Load register B with a REM token.

1C53

LD (HL),B

Save the REM token in register B at the memory location of the input buffer pointer in register pair HL.

1C54

INC HL

Bump the value of the input buffer pointer in register pair HL (because we just inserted a REM token).

1C55

EX DE,HL

Exchange the value of the input buffer pointer in register pair HL with the value of the input buffer pointer in register pair DE.

1C56

INC C

Bump the value of the counter in register C.

1C57

INC C

Bump the value of the counter in register C.

1C58-1C59

JR 1C77H

Jump to 1C77H to move the comment to the token buffer.

1C5A

EX DE,HL

Exchange the value of the input buffer pointer in register pair HL with the value of the input buffer pointer in register pair DE.

1C5B

INC HL

Bump the value of the input buffer pointer in register pair HL.

1C5C

LD (DE),A

Save the value of the token in register A at the location of the input buffer pointer in register pair DE.

1C5D

INC DE

Bump the value of the input buffer pointer in register pair DE.

1C5E

INC C

Bump the value of the counter in register C (which is the index/counter for the next syntax element).

1C5F-1C60

SUB 3AH

Check to see if the character in register A is a : to flag a multi-statement line.

1C61-1C62

JR Z,1C67H

Jump to 1C67H if the character in register A is a colon and we have a multi-statement line.

1C63-1C64

CP 4EH

Check to see if the token in register A is a DATA token.

1C65-1C66

JR NZ,1C6AH

Jump to 1C6AH if the token in register A is NOT a DATA token.

1C67-1C69

LD (40B0H),A

Save the value in register A as the tokenization flag for DATA.
NOTE: 40B0H holds the temporary storage location.

1C67-1C69

LD (409FH),A

1C6A-1C6B

SUB 59H

Check to see if the token in register A is a REM token.

1C6C-1C6E

JP NZ,1BCCH

Jump to 1BCCH if the token in register A isn't a REM token.

1C6F

LD B,A

Load register B with a zero.

1C70

LD A,(HL)

Load register A with the character at the location of the input buffer pointer in register pair HL.

1C71

OR A

Check to see if the character in register A is an end of the input character.

1C72-1C73

JR Z,1C7DH

Jump out of this loop to 1C7DH if the character in register A is an end of the input character.

1C74

CP B

Check to see if the character in register B matches the character in register A.

1C75-1C76

JR Z,1C5BH

Jump to 1C5BH if the character in register B matches the character in register A.

1C77

INC HL

Bump the value of the input buffer pointer in register pair HL.

1C78

LD (DE),A

Save the character in register A at the location of the input buffer pointer in register pair DE.

1C79

INC C

Bump the value of the counter in register C.

1C7A

INC DE

Bump the value of the input buffer pointer in register pair DE.

1C7B-1C7C

JR 1C70H

Loop until a 'end of statement' or a ending quote is found.

Still Inside the TOKENIZE INPUT ROUTINE - This routine is called if the character in register A is an end of the input character.

1C7D-1C7F

LD HL,0005H

Load register pair HL with a five.

1C80

LD B,H

Load register B with zero.

1C81

ADD HL,BC

Add 5 to the length of the token buffer so far.

1C82

LD B,H

Load register B with the MSB of the value in register H.

1C83

LD C,L

Load register C with the LSB of the value in register L.

1C84-1C86

LD HL,(40A7H)

Load register pair HL with the start address of the input buffer.
NOTE: 40A7H-40A8H holds the pointer to the start of the Input Buffer.

1C87

DEC HL

Decrement the value of the input buffer pointer in register pair HL.

1C88

DEC HL

Decrement the value of the input buffer pointer in register pair HL.

1C89

DEC HL

Decrement the value of the input buffer pointer in register pair HL.

1C8A

LD (DE),A

Zero the location of the input buffer pointer in register pair DE.

1C8B

INC DE

Bump the value of the input buffer pointer in register pair DE.

1C8C

LD (DE),A

Zero the location of the input buffer pointer in register pair DE.

1C8D

INC DE

Bump the value of the input buffer pointer in register pair DE.

1C8E

LD (DE),A

Zero the location of the input buffer pointer in register pair DE.

1C8F

RET

Return.

1C90-1C95 - RST 0018H CODE
The RST 18H code is located here. (Unsigned compare (HL-DE)).

This is the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

1C90HCHLDE

LD A,H

Load register A with the MSB of the value in register H.

1C91

SUB D

Subtract the value of the MSB of the value in register D from the MSB of the value in register A.

1C92

RET NZ

Return if the MSB of the value in register D doesn't equal the MSB of the value in register H.

1C93

LD A,L

Load register A with the LSB of the value in register L.

1C94

SUB E

Subtract the LSB of the value in register E from the LSB of the value in register A.

1C95

RET

Return.

1C96-1CA0 - RST 0008H CODE

The RST 8H code is located here.
This is the COMPARE SYMBOL routine which comparess the symbol in the input string pointed to by HL register to the value in the location following the RST 08 call. If there is a match, control is returned to address of the RST 08 instruction 2 with the next symbol in the Aregister and HL incremented by one. If the two characters do not match, a syntax error message is given and control returns to the Input Phase).

1C96

LD A,(HL)

Load register A with the character at the location of the current BASIC program pointer in register pair HL.

1C97

EX (SP),HL

Save the return address of the routine by exchanging the value of the current BASIC program pointer in register pair HL with the value of the return address to the stack.

1C98

CP (HL)

Check to see if the character at the location following the RST 08H call (stored in register pair HL) is the same as the character in register A.

1C99

INC HL

Bump the value of the return address in register pair HL.

1C9A

EX (SP),HL

Restore the return address (meaning the RST 08H plus 1 byte plus 1 byte) to the stack pointer.

1C9B-1C9D

JP Z,1D78H

Jump to the RST 0010H code if the characters match.

1C9E-1C90

JP 1997H

If they don't match, jump to the ?SN ERROR routine.

1CA1-1D1D - Level II BASIC FOR ROUTINE

1CA1-1CA2

LD A,64H

Load register A with the value for the FOR flag.

1CA3-1CA5

LD (40DCH),A

Save the value in register A as the current value of the FOR flag.
NOTE: 40DCH holds FOR flag.

1CA6-1CA8

CALL 1F21H

Go evaluate the N=M portion of the expression.

1CA9

EX (SP),HL

Exchange the value of the current BASIC program pointer in register pair HL with the value to the stack.

1CAA-1CAC

CALL 1936H

GOSUB to 1936H to check to see if there is a FOR statement to the stack already using the same variable name (called the index).

1CAD

POP DE

Get the current BASIC program pointer from the stack (which should be the TO token and put it in register pair DE.

1CAE-1CAF

JR NZ,1CB5H

If there isn't a matching FOR statement to the stack, skip the next 4 instructions (which are preparing for a NEXT WITHOUT FOR error) and jump to 1CB5H. If one is found, on exit HL will equal the starting address of the FOR push.

1CB0

ADD HL,BC

Add the value in register pair BC (which is the offset to the end of the stack frame) to the value in register pair HL. After this addition, we should be pointing to the end of the first FOR frame push.

1CB1

LD SP,HL

Reset the stack pointer to end of the first FOR frame push. This also frees up the stack space and prepares for a NF error.

1CB2-1CB4

LD (40E8H),HL

Save the value in register pair HL as the stack pointer, get ready for a NF error.
NOTE: 40E8H-40E9H holds Stack pointer pointer.

1CB5

EX DE,HL

Exchange the value of the current BASIC program pointer in register pair DE with the value of the stack pointer address in register pair HL.

1CB6-1CB7

LD C,08H

Load register C with the 1/2 the amount of space needed.

1CB8-1CBA

CALL 1963H

Go check to see if there is enough memory (i.e., 16 bytes) left by calling 1963H (which is the MEMORY CHECK ROUTINE).

1CBB

PUSH HL

Save the value of the current BASIC program pointer (which is the code string address before the TO) in register pair HL to the stack.

1CBC-1CBE

CALL 1F05H

Keep scanning the current BASIC program (pointer is in register pair HL) until it points to the end of the BASIC statement.

1CBF

EX (SP),HL

Exchange the adjusted value of the current BASIC program pointer in register pair HL with the value of the current BASIC program pointer to the stack.

1CC0

PUSH HL

Save the value of the current BASIC program pointer in register pair HL to the stack. This should be pointing to the TO token.

1CC1-1CC3

LD HL,(40A2H)

Load register pair HL with the value (in binary) of the current BASIC line number.
NOTE: 40A2H-40A3H holds the current BASIC line number.

1CC4

EX (SP),HL

Exchange the value of the current BASIC line number in register pair HL with the value of the current BASIC program pointer to the stack.

1CC5-1CC6

RST 08H ⇒ BDH

Since the character at the location of the current BASIC program pointer in register pair HL must be TO token (BDH) so call the COMPARE SYMBOL routine which comparess the symbol in the input string pointed to by HL register to the value in the location following the RST 08 call. If there is a match, control is returned to address of the RST 08 instruction 2 with the next symbol in the Aregister and HL incremented by one. If the two characters do not match, a syntax error message is given and control returns to the Input Phase).

1CC7

RST 20H

If the Variable Type is ...	and the Flags are set ...	... then Register A will be set ...
Integer	NZ/C/M/E	-1
String	Z/C/P/E	0
Single Precision	NZ/C/P/O	1
Double Precision	NZ/NC/P/E	5

1CC8-1CCA

JP Z,0AF6H

If that test shows we have a STRING, go to the Level II BASIC error routine and display a TM ERROR message.

1CCB-1CCD

JP NC,0AF6H

If that test shows we have a DOUBLE PRECISION number, go display a ?TM ERROR message.

1CCE

PUSH AF

We have an integer, so let's keep going and save the value in register pair AF (the type flags) to the stack.

lCCFH-lCDl

CALL 2337H

Go evaluate the expression at the location of the current BASIC program pointer in register pair HL (which should be the TO side) and return with the result in REG 1.

1CD2

POP AF

Restore the index type flags from the from the stack and put it in register pair AF.

1CD3

PUSH HL

Save the value of the current BASIC program pointer (which is the code string after the TO pointer) in register pair HL to the stack.

1CD4-1CD6

JP P,1CECH

Jump if the current number type is single precision.

1CD7-1CD9

CALL 0A7FH

Call the CONVERT TO INTEGER routine at 0A7FH (where the contents of REG 1 are converted from single or double precision to integer and deposited into HL).

1CDA

EX (SP),HL

Exchange the integer value in register pair HL (the current TO value) with the value of the current BASIC program pointer to the stack.

1CDB-1CCD

LD DE,0001H

Load register pair DE with a default STEP value of 1.

1CDE

LD A,(HL)

Load register A with the character at the location of the current BASIC program pointer in register pair HL.

1CDF-1CE0

CP CCH

Check to see if the character in register A is CCH which is the STEP token.

1CE1-1CE3

CALL Z,2B01H

So now we have a STEP token so we have to get the step value into DE. To do this, GOSUB to 2B01H to evaluate the expression at the location of the current BASIC program pointer in register pair HL and return with the integer value in register pair DE if the character in register A is a STEP token.

1CE4

PUSH DE

Save the STEP index value (in register pair DE) to the stack.

1CE5

PUSH HL

Save the current BASIC program pointer (in register pair HL) to the stack.

1CE6

EX DE,HL

Exchange the STEP value (from DE) with the value of the current BASIC program pointer (in register pair HL). Now HL will have the value so the next call can test its size.

1CE7-1CE9

CALL 099EH

GOSUB to 099EH to get the sign of the STEP value into A. It will be A=+1 if positive and A=-1 if negative.

1CEA-1CEB

JR 1D0EH

Jump down to 1D0EH to skip the convert to single precision code which follows.

1CEC-1CEE

CALL 0AB1H

Need the TO value to be integer so GOSUB to the CONVERT TO SINGLE PRECISION routine at 0AB1H (which converts the contents of REG 1 from integer or double precision into single precision).

1CEF-1CF1

Call 09BF which loads the SINGLE PRECISION value in REG 1 (the TO value in integer) into register pair BC/DE.

1CF2

POP HL

Get the value of the current BASIC program pointer from the stack (which should be the end of the TO expression) and put it in register pair HL.

1CF3H,1CF4

PUSH BC
PUSH DE

Save all 4 bytes of the TO value to the stack.

1CF5-1CF7

LD BC,8100H

Load register pair BC with the exponent and the MSB for a single precision constant.

1CF8

LD D,C

Zero the NMSB for the single precision constant in register D.

1CF9

LD E,D

Zero the LSB for the single precision constant in register E. Register pairs BC and DE now hold a single precision constant equal to one.

1CFA

LD A,(HL)

Load register A with the character at the location of the current BASIC program pointer in register pair HL.

1CFB-1CFC

CP CCH

Check to see if the character in register A is a STEP token.

1CFD-1CFE

LD A,01H

Load register A with the default STEP value (in this case, 1).

1CFF-1D00

JR NZ,1D0FH

Skip over the next unstructions by jumping down to 1D0FH if the character at the location of the current BASIC program pointer in register A isn't a STEP token.

1D01-1D03

CALL 2338H

Go evaluate the expression at the location of the current BASIC program pointer (which is the STEP instruction and return with the result in REG 1

1D04

PUSH HL

Save the value of the current BASIC program pointer in register pair HL to the stack.

1D05-1D07

CALL 0AB1H

Convert the STEP value to single precision by calling the CONVERT TO SINGLE PRECISION routine at 0AB1H (which converts the contents of REG 1 from integer or double precision into single precision).

1D08-1D0A

Load the STEP value into BC/DE by calling 09BF which loads the SINGLE PRECISION value in REG 1 into register pair BC/DE.

1D0B-1D0D

Go get the sign for the STEP value (held in REG 1) into register A. A will be +1 if positive, and -1 if negative.

1D0E

POP HL

Get the value of the current BASIC program pointer from the stack and put it in register pair HL.

1D0F

PUSH BC

Save the exponent and the NMSB for the single precision value in register pair BC to the stack.

1D10

PUSH DE

Save the NMSB and the LSB for the single precision value in register pair DE to the stack.

1D11

LD C,A

Load register C with the sign value for the STEP value in register A.

1D12

RST 20H

If the Variable Type is ...	and the Flags are set ...	... then Register A will be set ...
Integer	NZ/C/M/E	-1
String	Z/C/P/E	0
Single Precision	NZ/C/P/O	1
Double Precision	NZ/NC/P/E	5

1D13

LD B,A

Load register B with type-adjusted and sign value of the number type flag test in register A.

1D14

PUSH BC

Save the type-adjusted and sign value in register pair BC to the stack.

1D15

PUSH HL

Save the value of the current BASIC program pointer in register pair HL to the stack.

1D16-1D18

LD HL,(40DFH)

Load register B with a FOR x=y token.
NOTE: 40DFH-40E0H holds Used by DOS.

1D19

EX (SP),HL

Put the code address string into HL and put the address of the x variable into the stack.

1D1A-1D1B

LD B,81H

Load register B with the FOR token.

1D1C

PUSH BC

Save the FOR and token and the sign of the STEP increment BC to the stack.

1D1D

INC SP

Bump the value of the stack pointer to leave a one byte gap. By continuing onward, we will wind up continuing the execution of the code string.

1D1E-1D77 - LEVEL II BASIC INTERPRETER

1D1E-1D20

CALL 0358H

GOSUB to 0358H to check to see if a key has been pressed.

1D21

OR A

Set the flags to test for what key was pressed.

1D22-1D24

CALL NZ,1DA0H

GOSUB to 1DA0H if the key pressed was a SHIFT-@. This will save the address of the last byte executed in the current line.

1D25-1D27

LD (40E6H),HL

Save the value of the current BASIC program pointer.
NOTE: 40E6H-40E7H holds the temporary storage location.

1D28-1D2B

LD (40E8H),SP

Save the value of the stack pointer.
NOTE: 40E8H-40E9H holds Stack pointer pointer.

1D2C

LD A,(HL)

Load register A with the value at the location of the current BASIC program pointer in register pair HL.

1D2D-1D2E

CP 3AH

Check to see if the character in register A is a :.

1D2F-1D30

JR Z,1D5AH

If the character is a :, jump to 1D5AH since that means this is a brand new statement on this line.

1D31

OR A

There wasn't a colon, so the only valid thing we can find now is an END OF LINE character. This will check to see if the character in register A is an end of the BASIC line character.

1D32-1D34

JP NZ,1997H

Go to the Level II BASIC error routine and display a ?SN ERROR message if the character in register A isn't an end of the BASIC line character.

1D35

INC HL

So now we know that we have another line number to check, so bump the value of the current BASIC program pointer in register pair HL.

1D36

LD A,(HL)

Load register A with the LSB of the next BASIC line pointer at the location of the current BASIC program pointer in register pair HL.

1D37

INC HL

Bump the value of the current BASIC program pointer in register pair HL.

1D38

OR (HL)

Check to see if the next BASIC line pointer is equal to zero.

1D39-1D3B

JP Z,197EH

Jump to 197EH if this is the end of the BASIC program.

1D3C

INC HL

If we are here, it was not the end of the BASIC program so we need to bump the value of the current BASIC program pointer in register pair HL.

1D3D

LD E,(HL)

Load register E with the LSB of the BASIC line number at the location of the current BASIC program pointer in register pair HL.

1D3E

INC HL

Bump the value of the current BASIC program pointer in register pair HL.

1D3F

LD D,(HL)

Load register D with the MSB of the BASIC line number at the location of the current BASIC program pointer in register pair HL.

1D40

EX DE,HL

Exchange the value of the BASIC line number in register pair DE with the value of the current BASIC program pointer in register pair HL.

1D41-1D43

LD (40A2H),HL

Save the value of the BASIC line number in register pair HL.
NOTE: 40A2H-40A3H holds the current BASIC line number.

Honor a TRON by showing the line number if it is in effect.

1D44-1D46

LD A,(411BH)

Before we move on, we need to honor a TRON, if its in effect so first we load register A with the value of the TRON flag.
NOTE: 411BH holds the TRON/TROFF flag.

1D47

OR A

Check for TRON.

1D48-1D49

JR Z,1D59H

Jump out of this routine to 1D59H if TROFF.

1D4A

PUSH DE

If we are here, we have to process the code to show the "<nnnn>" of a TRON. First, save the value of the current BASIC program pointer in register pair DE to the stack.

1D4B-1D4C

LD A,3CH

Load register A with a <.

1D4D-1D4F

Go display the < that preceeds the line number in TRON output

1D50-1D52

CALL 0FAFH

Call the HL TO ASCII routine at 0FAFH (which converts the value in the HL register pair (assumed to be an integer) to ASCII and display it at the current cursor position on the video screen) to display the current BASIC line number.

1D53-1D54

LD A,3EH

Load register A with a >

1D55-1D57

Go display the > that follows the line number in TRON output

1D58

POP DE

Get the value of the current BASIC program pointer from the stack and put it in register pair DE.

Done with the TRON, so let us continue

1D59

EX DE,HL

Load register pair HL with the value of the current BASIC program pointer in register pair DE.

1D5A

RST 10H

We need to get the next token. We bump the current input buffer pointer in register pair HL until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1D5B-1D5D

LD DE,1D1EH

Load register pair DE with the return address to go to after executing one verb.

1D5E

PUSH DE

Save that return address in register pair DE to the stack.

1D5F

RET Z

Return (back to 1D1EH) if the character at the location of the current BASIC program pointer (in register pair HL) is an end of the BASIC line character.

1D60-1D61

SUB 80H

Check to see if the character at the location of the current BASIC program pointer in register A is a token. This is accomplished because tokens range from 80H-FBH so this would give an index of the current token.

1D62-1D64

JP C,1F21H

Jump to 1F21H if the character in register A isn't a BASIC token.

1D65-1D66

CP 3CH

Check to see if the token in register A is below the TAB( token.

1D67-1D69

JP NC,2AE7H

Jump out of here to 2AE7H if the token in register A is greater than or equal to a TAB( token, meaning TAB( to MID$(.

1D6A

RLCA

Multiply the token value in register A by two. This doubles the remainder of the routine address offset.

1D6B

LD C,A

Load the adjusted token value in register C from register A.

1D6C-1D6D

LD B,00H

Load register B with zero so that BC now holds "00" and (2 x the token).

1D6E

EX DE,HL

Load register pair DE with the value of the current BASIC program pointer in register pair HL.

1D6F-1D71

LD HL,1822H

Load register pair HL with the list of BASIC execution addresses.

1D72

ADD HL,BC

Add the value of the token offset in register pair BC to the starting address of the list of BASIC execution addresses in register pair HL.

1D73

LD C,(HL)

Load register C with the LSB of the execution address at the location of the memory pointer in register pair HL.

1D74

INC HL

Bump the value of the memory pointer in register pair HL.

1D75

LD B,(HL)

Load register B with the MSB of the execution address at the location of the memory pointer in register pair HL.

1D76

PUSH BC

Save the value of the execution address in register pair BC to the stack.

1D77

EX DE,HL

Load register pair HL with the value of the current BASIC program pointer in register pair DE (i.e., restore the code string address).

1D78-1D90 - RST 0010H CODE

The RST 10H code is located here. This is the EXAMINE NEXT SYMBOL routine which loads the next character from the string pointed to by the HL register set into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric. Blanks and control codes 09 and OB are ignored causing the following character to be loaded and tested. The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one. The string must be terminated by a byte of zeros).

1D78HFETCH

INC HL

Bump the value of the current BASIC program pointer in register pair HL to the next character.

1D79

LD A,(HL)

Load register A with the value of the character at the location of the current BASIC program pointer in register pair HL.

1D7A-1D7B

CP 3AH

Check to see if the character at the location of the current BASIC program pointer in register A is greater than or equal to a :. Results:

If A=: it sets the ZERO FLAG
If A<: then the CARRY FLAG will be set
if A>=: then the NO CARRY FLAG will be set.

1D7C

RET NC

Return if the character at the location of the current BASIC program pointer in register A is greater than or equal to a : (meaning :, ;, < ... Y, Z.

1D7D-1D7E

CP 20H

Check to see if the character at the location of the current BASIC program pointer in register A is a space.

1D7F-1D81

JP Z,1D78H

Loop if the character at the location of the current BASIC program pointer in register A is a space.

1D82-1D83

CP 0BH

Check to see if the character at the location of the current BASIC program pointer in register A is greater than or equal to 0BH (meaning it is not a control code). Results:

If A=0BH it sets the ZERO FLAG
If A<0BH then the CARRY FLAG will be set
if A>=0BH then the NO CARRY FLAG will be set.

1D84-1D85

JR NC,1D8BH

Jump if the character at the location of the current BASIC program pointer in register A if greater than or equal to 0BH.

1D86-1D87

CP 09H

Check to see if the character at the location of the current BASIC program pointer in register A is greater than or equal to 09H (meaning a horizontal tab). Results:

If A=09H it sets the ZERO FLAG
If A<09H then the CARRY FLAG will be set
if A>=09H then the NO CARRY FLAG will be set.

1D88-1D8A

JP NC,1D78H

Loop back up to get the next character if if the character at the location of the current BASIC program pointer in register A is greater than or equal to 09H.

1D8B-1D8C

CP 30H

Check to see if the character at the location of the current BASIC program pointer in register A is greater than or equal to a 0. Results:

If A=0 it sets the ZERO FLAG
If A<0 then the CARRY FLAG will be set
if A>=0 then the NO CARRY FLAG will be set.

1D8D

CCF

Complement (invert) the CARRY FLAG so that it will set the CARRY FLAG if that ascii character is numeric (i..e, greater than or equal to 30H).

1D8E

INC A

Clear the CARRY FLAG if it is not numeric (i.e., it is less than 30).

1D8F

DEC A

Set the status flags (except for the CARRY FLAG) according to the character at hand.

1D90

RET

Return.

1D91-1D9A - LEVEL II BASIC RESTORE ROUTINE

1D91

EX DE,HL

Save the contents of HL by loading its contents into DE.

1D92-1D94

LD HL,(40A4H)

Load register pair HL with the start of the BASIC program pointer.

Note: 40A4H-40A5H holds the starting address of BASIC program text also known as the PROGRAM STATEMENT TABLE (PST).

1D95

DEC HL

Backspace from the start of the BASIC program pointer.

1D96-1D98

LD (40FFH),HL

Save the start of the program pointer -1 into 40FFH.
NOTE: 40FFH-4100H holds READ pointer.

1D99

EX DE,HL

Restore the HL from being held in DE.

1D9A

RET

Return.

1D9B-1DAD - SCAN KEYBOARD ROUTINE

1D9B-1D9D

CALL 0358H

GOSUB to 0358H to scan the keyboard.

1D9E

OR A

Set the flags (to see if a key was pressed).

1D9F

RET Z

Return if a key wasn't pressed.

1DA0H - Inside the SCAN KEYBOARD ROUTINE - This will process a `SHIFT` + `@` (Pause) Keypress

1DA0-1DA1

CP 60H

Check to see if the key pressed in register A is a SHIFT + @.

1DA2-1DA4

CALL Z,0384H

If you got a SHIFT + @ we now need to honor that by waiting for yet another key to be pressed.

1DA5-1DA7

LD (4099H),A

Save the key pressed in register A as the value of the last key pressed.
NOTE: 4099H holds the Last key pressed.

1DA8

DEC A

Check to see if the BREAK key was pressed.

1DA9H-1DADH - Inside the SCAN KEYBOARD ROUTINE - This will process a STOP.

1DA9

RET NZ

Return if the BREAK key wasn't pressed.
This is the STOP entry point.

1DAA

INC A

Readjust the value of the key pressed in register A.

1DAB-1DAD

JP 1DB4H

Jump into the applicable portion of the code that processes END.

1DAE-1DE3 - LEVEL II BASIC END ROUTINE

1DAE

RET NZ

Return and display a ?SN ERROR message if there is anything following the END token.

1DAF

PUSH AF

Save the value in register pair AF to the stack.

1DB0-1DB2

CALL Z,41BBH

If this is a DOS system, then call the DOS link at 41BBH instead of continuing here.

1DB3

POP AF

Restore the END status to the A register.

1DB4-1DB6

LD (40E6H),HL

Save the value of the current BASIC program pointer in register pair HL.
NOTE: 40E6H-40E7H holds the temporary storage location.

1DB7-1DB9

LD HL,40B5H

Load register pair HL with the starting address of the temporary string work area.
NOTE: 40B5H-40D2H holds Temporary string work area.

1DBA-1DBC

LD (40B3H),HL

Save the value in register pair HL as the new temporary string work area pointer.
NOTE: 40B3H-40B4H holds Next available location in the temporary string work area pointer.

1DBD-1DBFH

21 F6 FF

Z-80 space saving trick

1DBE-1DBF

OR FFH

Set the flags.

1DC0

POP BC

Get the value from the stack and put it in register pair BC. This clears out the stack.

1DC1-1DC3

LD HL,(40A2H)

Load register pair HL with the value of the current BASIC line number in binary.
NOTE: 40A2H-40A3H holds the current BASIC line number.

1DC4

PUSH HL

Save the value of the current BASIC line number (in binary) in register pair HL to the stack.

1DC5

PUSH AF

Save the value in register pair AF to the stack. A will be 0 if it is an END and A will be a 1 if it is a STOP.

1DC6

LD A,L

These 3 instructions test to see if we are in command mode by testing for an uninitialized line (meaning a line number of FFFF). First, load register A with the LSB of the current BASIC line number in register L.

1DC7

AND H

Combine the MSB of the current BASIC line number in register H with the LSB of the current BASIC line number in register A.

1DC8

INC A

Bump the combined value of the current BASIC line number in register A.

1DC9-1DCA

JR Z,1DD4H

Increasing FFFF by 1 would flip the Z flag on, meaning there was no line number. If there was no line number, skip the nex 3 instructions and go to 1D44H.

1DCB-1DCD

LD (40F5H),HL

If we are here, we have a line number so save the line number we ended on in register pair HL.
NOTE: 40F5H-40F6H holds the last line number executed.

1DCE-1DD0

LD HL,(40E6H)

Load register pair HL with the value of the current BASIC program pointer .
NOTE: 40E6H-40E7H holds the temporary storage location.

1DD1-1DD3

LD (40F7H),HL

Save the value of the current BASIC program pointer in register pair HL.
NOTE: 40F7H-40F8H holds the last byte executed.

1DD4-1DD6

CALL 038BH

Go set the current output device to the video display.

1DD7-1DD9

CALL 20F9H

Go display a carriage return if necessary.

1DDA

POP AF

Restore A so we can see if this is an END (where A=0) or a STOP (where A=1).

1DDB-1DDD

LD HL,1930H

Load register pair HL with the starting address of the BREAK message.

1DDE-1DE0

JP NZ,1A06H

Jump to 1A06H if it was a BREAK or a STOP that halted program execution.

1DE1-1DE3

JP 1A18H

At this point it was either due to an END statement or an error while in command mode so jump to 1A18H (note: This uses a Z-80 trick as 1A18H is in the middle of a 2 Opcode instruction starting at 1A17H).

1DE4-1DF6 - LEVEL II BASIC CONT ROUTINE.

1DE4-1DE6

LD HL,(40F7H)

Load register pair HL with the value of the continuation address.
NOTE: 40F7H-40F8H holds the last byte executed.

1DE7-1DE8

LD A,H
OR L

Test HL for 0. The easiest way to test a 2 byte register for zero is to load the MSB into A and then OR it with the LSB. if the MSB was 0 and the LSB was 0, then A will be 0.

1DE9-1DEA

LD E,20H

Load register E with a ?CN ERROR code.

1DEB-1DED

JP Z,19A2H

If HL was zero, then a CONT isn't possible, so JUMP to 19A2H to display a ?CN ERROR.

1DEE

EX DE,HL

If we are here, there was a valid return line number, so load register pair DE with the value of the continuation line number in register pair HL.

1DEF-1DF1

LD HL,(40F5H)

Load HL with the value of the last BASIC line number executed.
NOTE: 40F5H-40F6H holds the last line number executed.

1DF2-1DF4

LD (40A2H),HL

Save the last line number executed in register pair HL (which had the error) as the current BASIC line number.
NOTE: 40A2H-40A3H holds the current BASIC line number.

1DF5

EX DE,HL

Swap so that HL will be the address of the continuation line.

1DF6

RET

Return (continue running but from the CONT line number).

1DF7H-1DFCH - TRON and TROFF Routine

1DF7H - TRON Entry Point (Set A with AFH)

1DF7-1DF8

LD A,AFH

Load register A with AFH (Decimal: 175), which is the value for TRON when placed into 411BH.

1DF8H - TROFF Entry Point (Set A with 00H)

1DF8

XOR A

Z-80 trick. This command is only visible if jumped to. This zeros register A.

1DF9-1DFC - COMMON CODE SHARED BY TRON AND TROFF - Put A into (411BH)

1DF9-1DFB

LD (411BH),A

Save the value in register A as the current value of the TRON/TROFF flag.
NOTE: 411BH holds the TRON/TROFF flag. 0=off (TROFF), 175=on (TRON)

1DFC

RET

RETURN.

1DFD-1DFF - DISK ROUTINE NOT USED BY LEVEL II BASIC.

1DFD

POP AF

1DFE

POP HL

1DFF

RET

1E00H-1E3CH - DEFxxx Routine

1E00-1E02 - INSIDE THE DEFxxx ROUTINE - DEFSTR Entry Point

1E00-1E01

LD E,03H

Load register E with the DEFSTR string number type flag (03H).

1E02H

32 1B 41

Z-80 Trick! See the general explanation at 10F8H.

1E03H-1E05H - INSIDE THE DEFxxx ROUTINE - DEFINT Entry Point

1E03-1E04

LD E,02H

Load register E with the DEFINT integer number type flag (02H).

1E05H

011 1E 04

Z-80 Trick! See the general explanation at 10F8H.

1E06H-1E08H - INSIDE THE DEFxxx ROUTINE - DEFSNG Entry Point

1E06-1E07

LD E,04H

Load register E with the DEFSNG single precision number type flag (04H).

1E08H

011 E0 08

Z-80 Trick! See the general explanation at 10F8H.

1E09-1E0AH - INSIDE THE DEFxxx ROUTINE - DEFDBL Entry Point

1E09-1E0A

LD E,08H

Load register E with the DEFDBL double precision number type flag (08H).

1E0BH-1E3CH - INSIDE THE DEFxxx ROUTINE - Common code shared by all the above - All of those can either have a - for a range of values or be separated by ,. This code needs to figure out the variables that followed the DEF??? instruction and then set the variable type (which is currently sitting in Register E) in the variable table.

1E0B-1E0D

CALL 1E3DH

GOSUB to 1E3DH to check the value at memory location (HL), which would be the current BASIC program pointer, to see if it is a letter. If its not, CARRY is set. If it is, CARRY is clear.

1E0E-1E10

LD BC,1997H

Load register pair BC with a return address which will return to the ?SN ERROR routine.

1E11

PUSH BC

Save the ?SN ERROR address (in register pair BC) to the stack.

1E12

RET C

Return if the character at the location of the current BASIC program pointer in register A isn't alphabetic (meaning that DEF??? wasn't followed by a letter).

1E13-1E14

SUB 41H

Subtract 41H from the letter's value in register A so that it will be in the range of 0-25.

1E15

LD C,A

Load register C with the adjusted value in register A.

1E16

LD B,A

Load register B with the adjusted value in register A.

1E17

RST 10H

Since we now need bump the value of the current BASIC program pointer until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1E18-1E19

CP CEH

Check to see if the character at the location of the current BASIC program pointer in register A is a -.

1E1A-1E1B

JR NZ,1E25H

If it's not a - we know this isn't a range, so jump to 1E25H because we don't need to get any more variables.

1E1C

RST 10H

If we are here, then we know the DEF??? has a range, so we need another character. We bump the value of the current BASIC program pointer until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1E1D-1E1F

CALL 1E3DH

GOSUB to 1E3DH to check the value at memory location (HL), which would be the current BASIC program pointer, to see if it is a letter. If its not, CARRY is set. If it is, CARRY is clear.

1E20

RET C

Return if the character at the location of the current BASIC program pointer in register A isn't alphabetic.

1E21-1E22

SUB 41H

Subtract 41H from the letter's value in register A so that it will be in the range of 0-25.

1E23

LD B,A

Load register B with the adjusted value in register A.

1E24

RST 10H

Since we now need bump the value of the current BASIC program pointer until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1E25

LD A,B

Load register A with the value of the second letter in register B.

1E26

SUB C

Subtract the value of the first letter in register C from the value of the second letter in Register A.

1E27

RET C

If the CARRY FLAG is set (meaning that varible names are not in ascending order ... the one in Register C is earlier than the one in Register A), return (to a syntax error).

1E28

INC A

Bump the value in register A so that it holds the number of variable names to be changed.

1E29

EX (SP),HL

Clear the error address and save the current code string address.

1E2A-1E2C

LD HL,4101H

Load register pair HL with 4101H which is the starting address of the variable declaration table.
NOTE: 4101H-411AH holds Variable Declaration Table.

1E2D-1E2E

LD B,00H

Load register B with zero.

1E2F

ADD HL,BC

Find the next entry in the type table by adding the value of the first letter in register pair BC to the value of the starting address of the variable declaration table in register pair HL.

1E30

LD (HL),E

E was set on entry to string, integer, single precision, or double precision as applicable. Save the number type flag in register E at the location of the memory pointer in register pair HL.

1E31

INC HL

Bump the value of the memory pointer in register pair HL.

1E32

DEC A

Decrement the count of the number of variables to be changed in register A.

1E33-1E34

JR NZ,1E30H

Loop until all of the variables in the DEFxxx range have been changed.

1E35

POP HL

Restore the code string pointer into register pair HL.

1E36

LD A,(HL)

Load A with the character at the location of the current BASIC program pointer in register pair HL.

1E37-1E38

CP 2CH

Check to see if the character at the location of the current BASIC program pointer in register A is a ,.

1E39

RET NZ

Return if the character at the location of the current BASIC program pointer in register A isn't a ,.

1E3A

RST 10H

Since we now need bump the value of the current BASIC program pointer until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1E3B-1E3C

JR 1E0BH

Loop until done with all the variables.

1E3D-1E44 - EXAMINE VARIABLE - See if the value pointed to at the memory location (HL) is an ASCII letter. C Flag is set for yes, NC Flag for no.

1E3D

LD A,(HL)

Load register A with the character at the location of the current BASIC program pointer in register pair HL.

1E3E-1E3F

CP 41H

Check to see if the character at the location of the current BASIC program pointer in register A is less than an A. Results:

If A=A it sets the ZERO FLAG
If A<A then the CARRY FLAG will be set
If A>=A then the NO CARRY FLAG will be set

1E40

RET C

Return if the character at the location of the current BASIC program pointer in register A is less than an A.

1E41-1E42

CP 5BH

Check to see if the character at the location of the current BASIC program pointer in register A is greater than a Z. Results:

If A=Z it sets the ZERO FLAG
If A<Z then the CARRY FLAG will be set
If A>=Z then the NO CARRY FLAG will be set

1E43

CCF

Complement the value of the CARRY FLAG. On exit this routine will have the CARRY FLAG set if the character at the location of the current BASIC program pointer in register A isn't alphabetic and will have the CARRY FLAG cleared if the character at the location of the current BASIC program pointer in register A is alphabetic.

1E44

RET

Return.

1E45-1E4E - EXAMINE VARIABLE

This is called when evaluating a subscript for a variable reference. It will evaluate if the value is positive or negative.

1E45

RST 10H

Get the next symbol from the input. Bump the value of the current BASIC program pointer until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1E46-1E48

CALL 2B02H

GOSUB to 2B02H to evaluate the expression at the current location of the BASIC program pointer in register pair HL and return with the integer result in register pair DE.

1E49

RET P

Return if the integer result in register pair DE is positive. If it is negative, flow down to the ?FC ERROR.

1E4A - FC ERROR entry point.

1E4A-1E4B

LD E,08H

Load register E with an ?FC ERROR code.

1E4C-1E4E

JP 19A2H

Display a ?FC ERROR message. If this is from a pass through, the error wll show if the integer result in register pair DE is negative.

1E4F-1E79 - ASCII TO BINARY

1E4F

LD A,(HL)

Load register A with the character at the location of the current BASIC program (which is pointed to by register pair HL).

1E50-1E51

CP 2EH

Check to see if the character at the location of the current BASIC program pointer in register A is a .. Results:

If A=. it sets the ZERO FLAG
If A<. then the CARRY FLAG will be set
If A>=. then the NO CARRY FLAG will be set

1E52

EX DE,HL

Load register pair DE with the value of the current BASIC program pointer in register pair HL.

1E53-1E55

LD HL,(40ECH)

Load register pair HL with the current BASIC line number.
NOTE: 40ECH-40EDH holds EDIT line number.

1E56

EX DE,HL

Exchange the value of the current BASIC program pointer in register pair DE with the current BASIC line number in register pair HL.

1E57-1E59

JP Z,1D78H

Jump to the RST 10H (EXAMINE NEXT SYMBOL) routine if the character at the location of the current BASIC program pointer in register A is a ..

1E5A - "DECBIN" - Converts numeric ASCII string pointed to by the HL register pair, to HEX and places the result in the DE register pair. After execution HL points to the delimiter and the A register contains the delimiter value. The Z flag is set if the delimiter equals 00 or 3A. Z is reset if any other delimiter is used. If there is no string at the location pointed to by HL the routine will return a MO ERROR (missing operand). If the result in the DE register pair exceeds FFFFH an OV ERROR (overflow) results.

1E5AH

DEC HL

Backspace HL (the current BASIC program pointer) to the current character.

1E5B-1E5D

LD DE,0000H

Load register pair DE with zero.

1E5E

RST 10H

Re-process that previous character through a RST 10H call.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1E5F

RET NC

Return if the character at the location of the current BASIC program pointer in register A isn't numeric.

1E60

PUSH HL

Save the value of the current BASIC program pointer in register pair HL to the stack.

1E61

PUSH AF

Save the value in register pair AF (which is the digit plus flags resulting from the RST 10H call) to the stack.

1E62-1E64

LD HL,1998H

Load register pair HL with 6552.

Why 6552? Well, since the Z-80 has no multiply function, checking for any possible arbitrary number would require 4 branches for each step in the 'add to itself until it hits * 10' plus another 4 when adding the last digit. The TRS-80 ROM didn't have that kind of room, nor the time to do all that, so they needed a cheat and that cheat was to let it go as high 65529. After all, 6552 + 1 more digit can NEVER exceed 65535, but 6553 + 1 digit sure can!

So with this trick, the ROM just needs to first check the number against 6552, which, when multiplied by 10, and adding one more digit, will never exceed 65529 (because 9 is the highest one number can go).

By using this trick, only 1 comparison is needed (is it greater or less than 6552) ... at the cost of 4 usable line numbers/memory size setting in the 6553x range.

Wait, you say. 65535-65529 is 6 numbers, so why do you say 4. Well, another shortcut the ROM uses is that it assumes anything at line number 65535 is being entered in direct mode (i.e., no line number; just a command), so 65535 couldn't be a line number. Similarly, in 1A09, 65534 is reserved to trigger the BASIC interpreter to jump to the initial powerup routine in the ROM (i.e., a reboot) so you couldn't use that line number either.

1E65

RST 18H

Now we need to check to see if the integer value in DE is greater than 6552, so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

1E66-1E68

JP C,1997H

Go to the Level II BASIC error routine and display a SN ERROR message if the value in register pair DE is greater than 6552.

1E69

LD H,D

Load register H with the MSB of the integer total in register D.

This is so we can multiply HL (which should hold the number 6552) by 10.

1E6A

LD L,E

Load register L with the LSB of the integer total in register E.

This is so we can multiply HL (which should hold the number 6552) by 10.

1E6B

ADD HL,DE

Multiply the integer value in register pair HL by two.

1E6C

ADD HL,HL

Add HL to itself, which is the same as multiplying the integer value in register pair HL by two. The integer result in register pair HL is now equal to the integer value in register pair DE times four.

1E6D

ADD HL,DE

Add the integer value in register pair DE to the integer value in register pair HL. The integer result in register pair HL is now equal to the integer value in register pair DE times five.

1E6E

ADD HL,HL

1E6F

POP AF

Put the last ASCII digit (from the stack) into AF.

1E70-1E71

SUB 30H

Convert the ASCII digit in register A to binary.

1E72

LD E,A

Load register E with the binary value of the character in register A.

1E73-1E74

LD D,00H

Load register D with zero so that DE will be 0000 through 0009 (the binary equivalent of the digit).

1E75

ADD HL,DE

Add the binary value of the character in register pair DE to the integer value in register pair HL

As noted above, adding in any digit can only result in HL going to 65529.

1E76

EX DE,HL

Swap DE and HL. This will have the effect of setting DE to be 10(base 10) * DE + A.

1E77

POP HL

Restore the pointer to the next digit (from the stack) into HL.

1E78-1E79

JR 1E5EH

Loop until the ASCII to binary conversion has been completed.

1E7A-1EA0 - LEVEL II BASIC CLEAR ROUTINE.

If Z FLAG is set, no number of bytes was provided (i.e., CLEAR instead of CLEAR 20).

1E7A-1E7C

JP Z,1B61H

Jump to 1B61H (which will set all 26 variables to single precision) if there isn't a number of bytes specified to clear for string space.

1E7D-1D7F

CALL 1E46H

GOSUB to 1E46H to evaluate the number of bytes to be reserved for string space and return with the integer result in register pair DE.

1E80

DEC HL

Decrement the current BASIC program pointer in register pair HL.

1E81

RST 10H

Evaluate the next instruction through a RST 10H call. This will bump the value of the current BASIC program pointer until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1E82

RET NZ

Return out of the routine if the character at the location of the current BASIC program pointer isn't an end of the BASIC statement character.

1E83

PUSH HL

Save the value of the current BASIC program pointer in register pair HL to the stack.

1E84-1E86

LD HL,(40B1H)

Load the top of memory pointer into register pair HL.
NOTE: 40B1H-40B2H holds MEMORY SIZE? pointer.

1E87

LD A,L

Load register A with the LSB of the top of memory pointer in register L.

1E88

SUB E

Subtract the LSB of the number of bytes for string space in register E from the LSB of the top of memory pointer in register A.

1E89

LD E,A

Load register E with the LSB of the start of string space in register A.

1E8A

LD A,H

Load register A with the MSB of the top of memory pointer in register H.

1E8B

SBC A,D

Subtract the MSB of the number of bytes for string space in register D from the MSB of the top of memory pointer in register A.

1E8C

LD D,A

Load register D with the MSB of the start of string space pointer in register A.

1E8D-1E8F

JP C,197AH

If the CARRY FLAG was triggered there isn't enough memory for the amount of string space specified, so go show a ?OM ERROR message.

1E90-1E92

LD HL,(40F9H)

Load register pair HL with the end of the BASIC program pointer.

Note: 40F9H-40FAH holds the starting address of the simple variable storage area.

1E93-1E95

LD BC,0028H

Load register pair BC with the least amount of space needed for BASIC program variables.

1E96

ADD HL,BC

Add the value in register pair BC to the end of BASIC program pointer in register pair HL.

1E97

RST 18H

Now we need to check to the adjusted end of the BASIC program pointer (in HL) with the start of the string space pointer (in DE), so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

1E98-1E9A

JP NC,197AH

Display an ?OM ERROR message if the start of string space pointer in register pair DE is less than the adjusted end of the BASIC program pointer in register pair HL.

1E9B

EX DE,HL

Put the new start of the string area address into HL.

1E9C-1E9E

LD (40A0H),HL

Load the start of string space pointer with HL.
Note: 40A0H-40A1H holds the start of string space pointer.

1E9F

POP HL

Restore the code string pointer back into HL.

1EA0-1EA2

JP 1B61H

Jump to 1B61H.

1EA3-1EB0 - LEVEL II BASIC RUN ROUTINE.

If Z FLAG is set, no line number was provided (i.e., RUN instead of RUN nnnn).

1EA3-1EA5

JP Z,1B5DH

JUMP to 1B5DH if there isn't a line number specified after the RUN token.

1EA6-1EA8

CALL 41C7H

GOSUB to 41C7H which is where the RUN nnnn code would be under DOS.

If we are here, then the command was RUN nnnn and we are in Cassette BASIC.

1EA9-1EAB

CALL 1B61H

GOSUB to 1B61H to initialize the BASIC variables and pointers.

1EAC-1EAE

LD BC,1D1EH

Load register pair BC with the continuation addres in the execution driver.

1EAF-1EB0

JR 1EC1H

Jump to 1EC1H to use the GOTO code to begin execution at the nnnn line.

1EB1-1EC1 - LEVEL II BASIC GOSUB ROUTINE

Can be used to execute the equivalent of a GOSUB statement from an assembly program. It allows a BASIC subroutine to be called from an assembly subroutine. After the BASIC subroutine executes, control returns to the next statement in the assembly program. All registers are used. On entry, the HL must contain an ASCII string with the starting line number of the subroutine.

1EB1-1EB2

LD C,03H

Load register B with the number of bytes needed for the GOSUB push.

1EB3-1EB5

CALL 1963H

Go make sure that there's enough memory for the GOSUB push.

1EB6

POP BC

Get the return address from the stack and put it in register pair BC.

1EB7

PUSH HL

Save the value of the current BASIC program pointer in register pair HL to the stack.

1EB8

PUSH HL

Create a hole to be filled in later by once again saving the value of the current BASIC program pointer to the stack.

1EB9-1EBB

LD HL,(40A2H)

Load register pair HL with the value of the current BASIC line number in binary.
NOTE: 40A2H-40A3H holds the current BASIC line number.

1EBC

EX (SP),HL

Put the binary value for the current line number into the hole in the stack AND restore the code string pointer.

1EBD-1EBE

LD A,91H

Load register A with a GOSUB token.

1EBF

PUSH AF

Save the GOSUB marker (in register pair AF) to the stack.

1EC0

INC SP

Bump the value of the stack pointer.

1EC1

PUSH BC

Save the return address in register pair BC (which is to the GOTO code) to the stack.

1EC2-1EDD - LEVEL II BASIC GOTO ROUTINE.

1EC2-1EC4

We need to put the line number to branch to into DE so we GOSUB to the ASCII TO INTEGER routine at 1E5A.
NOTE: The routine at 1E5A converts the ASCII string pointed to by HL to an integer deposited into DE. If the routine finds a non-numerica character, the conversion is stopped.

1EC5-1EC7

CALL 1F07H

GOSUB to 1F07H to bump the current BASIC program pointer in register pair HL until it points to the end of the current BASIC line.

1EC8

PUSH HL

Save the value of the current BASIC program pointer in register pair HL to the stack.

1EC9-1ECB

LD HL,(40A2H)

Load register pair HL with the binary equivalent of the last line number.
NOTE: 40A2H-40A3H holds the current BASIC line number.

1ECC

RST 18H

Now we need to compare the value of the current BASIC line number (in HL) with the value of the line number to branch to (in DE), so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

1ECD

POP HL

Get the value of the current BASIC program pointer from the stack and put it in register pair HL.

1ECE

INC HL

Bump the value of the current BASIC program pointer in register pair HL so as to restore the code string address. DE holds the line number specified.

1ECF-1ED1

CALL C,1B2FH

If the line number to branch to (in register pair DE) is greater than the current BASIC line number then GOSUB to 1B2FH to find where the line number is located at a LATER location.

1ED2-1ED4

CALL NC,1B2CH

If the line number to branch to (in register pair DE) is less than the current BASIC line number, then go find where the line number is located by calling the SEARCH FOR LINE NUMBER routine at 1B2CH which looks for the line number specified in DE. Returns C/Z with the line found in BC, NC/Z with line number is too large and HL/BC having the next available location, or NC/NZ with line number not found, and BC has the first available one after that.

1ED5

LD H,B

Load register H with the MSB of the new BASIC program pointer in register B. BC is still holding the address of the requested line number.

1ED6

LD L,C

Load register L with the LSB of the new BASIC program pointer in register C.

1ED7

DEC HL

Decrement the value of the current BASIC program pointer in register pair HL to get to the start of the line.

1ED8

RET C

If a line number was found, RETURN from this routine to the execution driver (to start execution at the new line number).

Inside the GOTO ROUTINE - If we are here, the line number nnnn was not found, so error out.

1ED9-1EDA

LD E,0EH

Load register E with an ?UL ERROR code.

1EDB-1EDD

JP 19A2H

Since the line number wasn't found, display a ?UL ERROR message.

1EDE-1E04 - LEVEL II BASIC RETURN ROUTINE

Returns control to the BASIC statement following the last GOSUB call. An assembly program called by a BASIC subroutine may wish to return directly to the orginal caller without returning through the subroutine entry point. This exit can be used for that return. The return address to the stack for the call to the assembly program must be cleared before returning via 1EDFH.

1EDE

RET NZ

Display a ?SN ERROR message if there is anything following the RETURN token.

1EDF-1EE0

LD D,FFH

Load register D with FFH (a dummy address for the search routine).

1EE1-1EE3

CALL 1936H

GOSUB to 1936H to backspace the stack pointer by four and return with the value at the location of the stack pointer in register A.

1EE4

LD SP,HL

Load the stack pointer with the new value in register pair HL.

1EE5-1EE7HS

LD (40E8H),HL

Save the stack pointer position in register pair HL.
NOTE: 40E8H-40E9H holds Stack pointer pointer.

1EE8-1EE9

CP 91H

Check to see if the value in register A is a GOSUB token.

1EEA-1EEB

LD E,04H

Load register E with a ?RG ERROR code.

1EEC - ?RG ERROR entry point.

1EEC-1EEE

JP NZ,19A2H

Display a ?RG ERROR message if there isn't a GOSUB push to the stack.

1EEF

POP HL

Get the binary value of the GOSUB line number from the stack and put it in register pair HL.

1EF0-1EF2

LD (40A2H),HL

Save the GOSUB line number in register pair HL as the current BASIC line number.
NOTE: 40A2H-40A3H holds the current BASIC line number.

1EF3

INC HL

Bump the value of the current BASIC line number in register pair HL.

1EF4

LD A,H
OR L

The way to test HL for 0 is to LOAD A,H and OR L, so A will be 0 only if BOTH H and L were 0. If HL=0 then HL was FFFFH and we have an overflow or a command mode.

1EF6-1EF7

JR NZ,1EFFH

Jump if Level II BASIC is in the command mode.

1EF8H-lEFA

LD A,(40DDH)

If we are here, we may have a one liner! Load register A with the command mode flag.
NOTE: 40DDH holds INPUT flag.

lEFB

OR A

Check for the command mode.

1EFC-1EFE

JP NZ,1A18H

Jump to 1A18H if Level II BASIC is in the command mode.

1EFF-1F01

LD HL,1D1EH

Load register pair HL with the return address.

1F02

EX (SP),HL

Exchange the value of the current BASIC program pointer to the stack with the return address in register pair HL.

1F03H

3E E1

Z-80 Trick! See the general explanation at 10F8H.

1F04

POP HL

Prepare to scan to the end of the GOSUB by restoring HL from the STACK.

1F05-1F20 - SCAN ROUTINE

This is also the DATA entry point.

1F05H

Z-80 Trick! See the general explanation at 10F8H.

1F06H

Z-80 Trick! See the general explanation at 10F8H.

1F07-1F08

LD C,00H

Load register C with zero.

1F09-1F0A

LD B,00H

Load register B with zero.

1F0B

LD A,C

Load register A with the stop scan character in register C.

1F0C

LD C,B

Load register C with the stop scan character in register B.

1F0D

LD B,A

Load register B with the stop scan character in register A.

1F0E

LD A,(HL)

Load register A with the character at the location of the current BASIC program pointer in register pair HL.

1F0F

OR A

Check to see if the character at the location of the current BASIC program pointer in register A is an end of the BASIC line character.

1F10

RET Z

Return if the character at the location of the current BASIC program pointer in register A is an end of the BASIC line character.

1F11

CP B

Check to see if the character at the location of the current BASIC program pointer in register A is the same as the stop scan character in register B.

1F12

RET Z

Return if the character at the location of the current BASIC program pointer in register A is the same as the stop scan character in register B.

1F13

INC HL

Bump the value of the current BASIC program pointer in register pair HL.

1F14-1F15

CP 22H

Check to see if the character at the location of the current BASIC program pointer in register A is a ".

1F16-1F17

JR Z,1F0BH

Loop if the character at the location of the current BASIC program pointer in register A is a quote.

1F18-1F19

SUB 8FH

Check to see if the character at the location of the current BASIC program pointer in register A is a IF token.

1F1A-1F1B

JR NZ,1F0EH

Loop back to 1F0EH if the character at the location of the current BASIC program pointer in register A isn't an IF token.

1F1C

CP B

Check to see if the character at the location of the current BASIC program pointer in register A is the same as the character in register B.

1F1D

ADC A,D

Add the value in register D to the value in register A.

1F1E

LD D,A

Load register D with the value in register A.

1F1F-1F20

JR 1F0EH

Loop back to 1F0EH until scan is completed.

1F21-1F6B - LEVEL II BASIC LET ROUTINE

1F21-1F23

CALL 260DH

Call the FIND ADDRESS OF VARIABLE routine at 260DH which searches the Variable List Table for a variable name which matches the name in the string pointed to in HL, and return the address of that variable in DE (and if there is no variable, it creates it, zeroes it, and returns THAT location).

1F24-1F25

RST 08H ⇒ D5H

Test if the variable name is followed by a =. Since the character at the location of the current BASIC program pointer in register pair HL must be an EQUAL sign (D5) so call the COMPARE SYMBOL routine which comparess the symbol in the input string pointed to by HL register to the value in the location following the RST 08 call. If there is a match, control is returned to address of the RST 08 instruction 2 with the next symbol in the Aregister and HL incremented by one. If the two characters do not match, a syntax error message is given and control returns to the Input Phase).

1F26

EX DE,HL

Exchange the address of the variable in register pair DE with the value of the current BASIC program pointer in register pair HL.

1F27-1F29

LD (40DFH),HL

Save the addres of the variable in register pair HL.
NOTE: 40DFH-40E0H holds Used by DOS.

1F2A

EX DE,HL

Exchange the value of the current BASIC program pointer in register pair DE with the address of the variable in register pair HL.

1F2B

PUSH DE

Save the address of the variable in register pair DE to the stack.

1F2C

RST 20H

If the Variable Type is ...	and the Flags are set ...	... then Register A will be set ...
Integer	NZ/C/M/E	-1
String	Z/C/P/E	0
Single Precision	NZ/C/P/O	1
Double Precision	NZ/NC/P/E	5

1F2D

PUSH AF

Save the value in register pair AF to the stack. A will be -1 for an integer, 0 for a string, 1 for single precision, and 5 for double precision.

1F2E-1F30

CALL 2337H

Go evaluate the expression at the location of the current BASIC program pointer in register pair HL and return with the result in REG 1.

1F31

POP AF

Get the value from the stack and put it in register pair AF.

1F32

EX (SP),HL

Exchange the address of the variable to the stack with the value of the current BASIC program pointer in register pair HL.

1F33-1F34

ADD A,03H

Adjust the value in register A so that it will hold the correct number type flag (i.e., A will be 2 for integer, 3 for string, 4 for single precision, and 8 for double precision).

1F35-1F37

CALL 2819H

Go to 2819H to convert the result in REG 1 to the same number type for the variable .

1F38-1F3A

CALL 0A03H

Go save the result of the expression.

1F3B

PUSH HL

Save the address of the variable in register pair DE to the stack.

1F3C-1F3D

JR NZ,1F66H

Jump if the result of the expression wasn't a string.

1F3E-1F40

LD HL,(4121H)

Load register pair HL with the starting address of the string's VARPTR in REG 1.

1F41

PUSH HL

Save the VARPTR for the string result in register pair HL to the stack.

1F42

INC HL

Bump the value of the VARPTR for the string result in register pair HL.

1F43

LD E,(HL)

Load register E with the LSB of the address for the string at the location of the VARPTR for the string in register pair HL.

1F44

INC HL

Bump the value of the VARPTR for the string result in register pair HL.

1F45

LD D,(HL)

Load register D with the MSB of the address for the string at the location of the VARPTR for the string in register pair HL.

1F46-1F48

LD HL,(40A4H)

Load register pair HL with the start of the BASIC program.

Note: 40A4H-40A5H holds the starting address of BASIC program text also known as the PROGRAM STATEMENT TABLE (PST).

1F49

RST 18H

Now we need to compare the start of the BASIC program area (in HL) with the address of the string result in DE, so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

1F4A-1F4B

JR NC,1F5AH

Jump if the address of the string result in register pair DE is less than the start of the BASIC program area in register pair HL.

1F4C-1F4E

LD HL,(40A0H)

Load register pair HL with the start of the string space pointer.
Note: 40A0H-40A1H holds the start of string space pointer.

1F4F

RST 18H

Now we need to compare the start of the string space pointer (in HL) with the address of the string result in DE, so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

1F50

POP DE

Get the VARPTR for the string result from the stack and put it in register pair DE.

1F51-1F52

JR NC,1F62H

Jump if the address of the string result in register pair DE was less than the start of the string space pointer in register pair HL.

1F53-1F55

LD HL,(40F9H)

Load register pair HL with the simple variables pointer.

Note: 40F9H-40FAH holds the starting address of the simple variable storage area.

1F56

RST 18H

Now we need to compare the address of the VARPTR for the string result in register pair DE with the simple variables pointer in register pair HL, so we call the COMPARE DE:HL routine, which numerically compares DE and HL. Will not work for signed integers (except positive ones). Uses the A-register only. The result of the comparison is returned in the status register as:

Condition	Flag
If HL < DE	CARRY SET
If HL > DE	NO CARRY
If HL ≠ DE	NZ
If HL = DE	Z

1F57-1F58

JR NC,1F62H

Jump if the address of the VARPTR for the string result in register pair DE is less than the simple variables pointer in register pair HL.

1F59-1F5AH

3E D1
LD A,D1H

Z-80 Trick

1F5A

POP DE

Get the VARPTR for the string result from the stack and put it in register pair DE.

1F5B-1F5D

CALL 29F5H

Go adjust the temporary string work area pointers.

1F5E

EX DE,HL

Exchange the VARPTR for the string in register pair DE with the string's address in register pair HL.

1F5F-1F61

CALL 2843H

Go move the string into string space.

1F62-1F64

CALL 29F5H

Go adjust the temporary string work area pointers.

1F65

EX (SP),HL

Exchange the address of the variable in register pair BL with the address of the variable to the stack.

1F66-1F68

CALL 09D3H

Go move the result to its proper location in memory.

1F69

POP DE

Get the address of the variable from the stack and put it in register pair DE.

1F6A

POP HL

Get the value of the current BASIC program pointer from the stack and put it in register pair HL.

1F6B

RET

Return.

1F6C-1FAE - LEVEL II BASIC ERROR ON ROUTINE

1F6C-1F6D

CP 9EH

Check to see if the character at the location of the current BASIC program pointer in register A is an ERROR token (since this is supposed to be ON ERROR.

1F6E-1F6F

JR NZ,1F95H

Jump down to 1F95H if the character at the location of the current BASIC program pointer in register A isn't an ERROR token.

1F70

RST 10H

If we are here, we have ON ERROR but we do need to see what's next. Since we now need bump the value of the current BASIC program pointer until it points to the next character, call the EXAMINE NEXT SYMBOL routine at RST 10H.
NOTE:

The RST 10H routine loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.
Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.
The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.
The string must be terminated by a byte of zeros.

1F71-1F72

RST 08H ⇒ 8DH

The next valid character at the location of the current BASIC program pointer in register pair HL must be a GOTO token (=8DH) so call the COMPARE SYMBOL routine which comparess the symbol in the input string pointed to by HL register to the value in the location following the RST 08 call. If there is a match, control is returned to address of the RST 08 instruction 2 with the next symbol in the Aregister and HL incremented by one. If the two characters do not match, a syntax error message is given and control returns to the Input Phase).

1F73-1F75

Convert the next constant into binary (with the result in DE). To do this, call the ASCII TO INTEGER routine at 1E5A.
NOTE: The routine at 1E5A converts the ASCII string pointed to by HL to an integer deposited into DE. If the routine finds a non-numerica character, the conversion is stopped.

1F76

LD A,D
OR E

To test DE for zero, LOAD A,D and then OR E. A will be 0 only if BOTH D and E were 0

1F78-1F79

JR Z,1F83H

Jump to 1F83H if the line number in register pair DE is equal to zero.

1F7A-1F7C

CALL 1B2AH

Go find the location of the line number in register pair DE and return with the location of the line number in register pair BC.

1F7DH,1F7E

LD D,B
LD E,C

Put the line number from BC into DE

1F7F

POP HL

Get the value of the current BASIC program pointer from the stack and put it in register pair HL.

1F80-1F82

JP NC,1ED9H

Display a ?UL ERROR message if the BASIC line doesn't exist.

1F83

EX DE,HL

Exchange the location of the BASIC line in register pair DE with the value of the current BASIC pro gram pointer in register pair HL.

1F84-1F86

LD (40F0H),HL

Save the location of the BASIC line in register pair HL.
NOTE: 40F0H-40F1H is used by ON ERROR.

1F87

EX DE,HL

Exchange the value of the current BASIC program pointer in register pair DE with the location of the BASIC line in register pair HL.

1F88

RET C

RETURN out of this routine to the execution driver if it was not ON ERROR GOTO 0000.

1F89-1F8B

LD A,(40F2H)

Load register A with the value of the error flag.
NOTE: 40F2H holds the error flag.

1F8C

OR A

Check to see if the error flag is set.

1F8D

RET Z

RETURN out of this routine to the execution driver if the override flag is not set.

1F8E-1F90

LD A,(409AH)

Load register A with the error code.
NOTE: 409AH holds the RESUME flag.

1F91

LD E,A

Load register E with the value of the error code in register A.

1F92-1F94

JP 19ABH

Go to the Level II error routine and display the error message for the error code in register E.

1F95 - Still in the ON routine, but we know it isn't ON ERROR. We now need to deal with the possibility that it was an ON n GOTO or ON n GOSUB.

1F95-1F97

CALL 2B1CH

First we need to get the n so go evaluate the expression at the location of the current BASIC program pointer and return with the result in register pair DE.

1F98

LD A,(HL)

Load register A with the next character (which should be a token) at the location of the current BASIC program pointer in register pair HL.

1F99

LD B,A

Save that token into register B.

1F9A-1F9B

CP 91H

Check to see if the character at the location of the current BASIC program pointer in register A is a GOSUB token.

1F9C-1F9D

JR Z,1FA1H

Skip the next 2 opcodes if the character at the location of current BASIC program pointer in register A is a GOSUB token .

1F9E-1F9F

RST 08H ⇒ 8DH

Now let's test to see if the next character is the token for a GOTO, call the COMPARE SYMBOL routine which comparess the symbol in the input string pointed to by HL register to the value in the location following the RST 08 call. If there is a match, control is returned to address of the RST 08 instruction 2 with the next symbol in the Aregister and HL incremented by one. If the two characters do not match, a syntax error message is given and control returns to the Input Phase).

1FA0

DEC HL

Decrement the value of the current BASIC program pointer in register pair HL to point to the GOTO token.

1FA1

LD C,E

Load register C with the LSB of the expression after the ON token in register E (i.e., the "n" from ON n GOTO).

1FA2

DEC C

Decrement the line number counter in register C.

1FA3

LD A,B

Load register A with the token in register B (which is either a GOSUB or GOTO token).

1FA4-1FA6

JP Z,1D60H

Jump to 1D60H if the line number has been found.

1FA7-1FA9

CALL 1E5BH

Evaluate the line number at the location of the current BASIC program pointer and return with the result in register pair DE.

1FAA-1FAB

CP 2CH

Check to see if the character at the location of the current BASIC program pointer in register A is a comma. If not, it is the ent of the statement.

1FAC

RET NZ

Return if the character at the location of the current BASIC program pointer in register A isn't a ,.

1FAD-1FAE

JR 1FA2H

Loop until the line number has been located.

1FAF-1FF3 - LEVEL II BASIC RESUME ROUTINE

1FAF-1FB1

LD DE,40F2H

Load register pair DE with the address of the Level II BASIC error flag.
NOTE: 40F2H holds the error flag.

1FB2

LD A,(DE)

Load register A with the error flag at the location of the memory pointer in register pair DE. It will be FF if there is an error, and a zero otherwise.

1FB3

OR A

Check for an error.

1FB4-1FB6

JP Z,19A0H

If there was no error, then display an ?RW ERROR message.

1FB7

INC A

Clear the error flag in register A.

1FB8-1FBA

LD (409AH),A

Save the new error flag in register A.
NOTE: 409AH holds the RESUME flag.

1FBB

LD (DE),A

Save the new error flag in register A at the location of the memory pointer in register pair DE.

1FBC

LD A,(HL)

Load register A with the character at the location of the current BASIC program pointer in register pair HL.

1FBD-1FBE

CP 87H

Check to see if the character at the location of the current BASIC program pointer in register A is a NEXT token.

1FBF-1FC0

JR Z,1FCDH

Jump down to 1FCDH if the character at the location of the current BASIC program pointer in register A is a NEXT token (as in RESUME NEXT).

1FC1-1FC3