TRS-80 Emulators - TRS-80 Model 4 Emulator for MS-DOS

Introduction

This program emulates a popular early microcomputer, the TRS-80 Model 4. It is an extremely fast emulation, written and optimized from the ground up in 80386 assembly language. The unregistered shareware version of the program emulates a 64K Model 4 with four floppy disk drives. The registered version adds support for Model 3 mode, the 128K memory upgrade, a high resolution graphics board, a virtual hard drive, a hardware clock, and RS-232 communications.

Either version of the Model 4 emulator will run on an IBM-compatible computer with an 80386 or better processor, 640K of memory, MS-DOS 3.0 or higher, VGA graphics, and a hard drive. A parallel printer and Sound Blaster-compatible sound card are optional. If you want to read physical TRS-80 disks using the emulator, your computer will need an appropriately-sized disk drive (usually 5?") and a capable floppy disk controller.

Note: This emulator will NOT run under Microsoft Windows. If you want a TRS-80 emulator that will run under Microsoft Windows, try TRS32.

M4.EXE emulates a Model 4 with the following hardware:

• Z-80 microprocessor (including all undocumented instructions) with 64K (unregistered shareware version) or 128K (registered version) of RAM
• FD1793 floppy disk controller
• 4 double-sided double-density 80 track drives
• Hard disk drive, with capacity of up to 13 megabytes (registered version only)
• Real time clock interrupt (30 ms in Model 3 mode, 60 ms in Model 4 mode)
• Hardware clock (registered version only)
• 80 by 24 screen with double-wide mode
• 64 by 16 screen with double-wide mode in Model 3 mode (registered version only)
• High resolution graphics board (Micro-Labs or Radio Shack, registered version only)
• Parallel printer port (only with PC parallel printer)
• Amplifier for sound output (through PC speaker or Sound Blaster card)
• RS-232 communications port (registered version only)
• Mouse driver (registered version only)

Obviously, no emulation can ever achieve complete software and hardware compatibility, but this emulator comes very close. It has been able to run all of the operating systems and applications software I have tried, including versions of LS-DOS, MULTIDOS for the Model 4, DOSPLUS for the Model 4, Montezuma Micro CP/M, LeScript, Allwrite, Scripsit Pro, PRO-MRAS, PRO-EnhComp, and many more.

The character sets used in this emulator include all of the characters in the Model 4 (and Model 3) character sets, including the international characters (with the exception of the katakana characters). The emulator also supports a double-wide display in both 80 by 24 and 64 by 16 modes.

To install the Model 4 emulator, create a directory for it on your hard drive and unzip the file M4V10.ZIP (unregistered shareware version) or M410REG.ZIP (registered version) into it. This directory should also hold any virtual disk files you want to use.

If you have the registered version of the emulator and plan to use Model 3 mode, you should also create a MODEL4.ROM file and place it in this directory. There are two ways to create MODEL4.ROM:

If you have a virtual disk image of LS-DOS 6.3.1, use the TRSREAD program (supplied with the registered version of the emulator) to extract the file MODELA/III. Copy it into your Model 4 emulator directory and rename it MODEL4.ROM.

If you have a real Model 4, start it up in Model 3 mode using an operating system such as LDOS. Go into BASIC, then type and run the following program:

10 OPEN "O",1,"MODEL4/ROM"
20 FOR X=0 TO &H37FF: PRINT#1,CHR$(PEEK(X));: NEXT X
30 CLOSE 1

Of course, there must be enough room on an available drive to hold this file. You will then need a means to transfer the file to your PC, such as TRSREAD (supplied with the registered version of the emulator) or a null modem transfer.

To start the Model 4 emulator, just type M4 at the MS-DOS prompt. On its first run, the emulator will calculate your machine speed and create a configuration file (M4.CFG) in the current directory. Subsequently, the emulator will read your machine speed and other options you have selected from that configuration file.

After the emulator displays its startup screen, it will wait for you to press a key. The first time you use the emulator, you will not have any virtual disk files "mounted" in the virtual drives, so it will prompt you to press F8 and do so.

To exit the emulator, press SHIFT+F7 and answer the question with a Y (for "Yes").

Only a few "hot keys" are needed to control the emulator. If you press any of these hot keys by accident (except for SHIFT F8), press ESC to return to the emulation.

One of the biggest differences between the PC keyboard and the Model 4 keyboard is the shifted number values. For instance, SHIFT+8 on a PC generates an asterisk (*), but on a Model 4 it generates a left parenthesis [(]. One way around this is to use the TRS-80 keyboard layout (described later), but another is to use the numeric keypad. With the NUMLOCK state on, pressing a key on the numeric keypad will generate a number, but if you press SHIFT and a number on the keypad, the result will be the same as if you had pressed SHIFT and a number on the Model 4 keyboard. For instance, pressing SHIFT and 8 on the numeric keypad will generate a left parenthesis [(], just like it would on a real Model 4.

The Model 4 emulator automatically adjusts itself to as close to true Model 4 speed as possible. However, there are times when this adjustment is not quite right, or when you want to run your emulated Model 4 faster or slower than normal. This is where the delay menu comes in.

To invoke the delay menu, press F5. You will see a menu with a list of saved delays. To select an existing delay, use the up and down arrow keys to highlight the appropriate name, then press ENTER.

To modify an existing delay, use the up and down arrow keys to highlight the appropriate name, then use the left and right arrow keys to adjust the delay value. Then press ENTER.

To delete the highlighted delay, press D.

To create a new delay, press N. Then type a name for the delay and press ENTER. Now you can change the delay value using the left and right arrow keys.

To exit from the delay menu, press ENTER or ESC.

Note: Snapshot support is included in the registered version of the emulator only.

A snapshot is a saved image of the emulated Model 4 at a particular point in time. You can be in the middle of an application (or a game), save a snapshot, exit the emulator, and turn off the computer. At some later time, when you re-enter the emulator and load that snapshot, you will be right back where you were, as though you had never left the machine.

(Note: Snapshots can be a very satisfying and helpful feature when you are playing a complicated game that does not have a "save game" option!)

To invoke the snapshot menu, press F6. You will see a directory of snapshot files (they have a .SNP extension). To save a snapshot, press S. You now have three options:

1. Press ESC to exit without saving a snapshot.
2. Type the filename of the snapshot you want to save, then press ENTER. (You do not need to include the .SNP extension.)
3. Press TAB to switch to directory mode, then use the arrow keys to highlight the snapshot filename you want to use. Then press ENTER.

Note that if you save a snapshot under the same filename as a previous snapshot, the previous snapshot will be erased.

To load a snapshot, press L. Again, you now have three options:

1. Press ESC to exit without loading a snapshot.
2. Type the filename of the snapshot you want to load, then press ENTER. (You do not need to include the .SNP extension.)
3. Press TAB to switch to directory mode, then use the arrow keys to highlight the snapshot you want to load. Then press ENTER.

To exit from the snapshot menu, press ENTER or ESC.

To invoke the virtual disk menu, press F8. You will see a menu with a directory display of virtual disk files at the top and a listing of virtual drives at the bottom. To place a virtual disk file in a virtual drive, press the number of the virtual drive (zero to three). You now have three options:

• Type the filename of the virtual disk file and press ENTER. (You do not need to include the .DSK extension.) If the virtual disk file does not exist, you will be asked if you want to create it. If you do want to create a new virtual disk file, remember that the new file is like a new, unformatted floppy disk. You will have to format it with the operating system of your choice before you can use it with the emulator.
• Press TAB to select a virtual disk file from the directory display. Use the arrow keys to highlight your selection. To change subdirectories, highlight the appropriate subdirectory name and press ENTER. When you have highlighted the proper virtual disk file, press ENTER.
• Press ENTER or ESC without typing anything else to leave the virtual drive empty.

To map a virtual drive to an actual PC drive, press the number of the virtual drive. Then type A: or B: (depending on which PC drive you want to use) and press ENTER.

To write protect a virtual drive, hold down the SHIFT key, then press the number of the virtual drive.

To reboot the emulator from within the virtual disk menu, press R. Otherwise, press ENTER or ESC to exit from the virtual disk menu.

Remember to treat virtual disk files with the same care as you would treat real TRS-80 disks. Don't swap virtual disks while the virtual drives are being accessed, and don't remove the system disk from virtual drive zero. Also, be aware that the emulator will not allow the same virtual disk file to be mounted in more than one virtual drive at a time.

IMPORTANT NOTE: LS-DOS requires that you turn on support for drives 2 and 3 before you can use them. Use these commands from the "LS-DOS Ready" prompt:

SYSTEM (DRIVE=2,ENABLE)
SYSTEM (DRIVE=3,ENABLE)

These commands can be SYSGENed, if you wish (use the LS-DOS HELP command for more information).

To invoke option menu #1, press F9. You will see a list of options (described below). To select an option, press its first letter (except for the Volume option -- see below). To exit from option menu #1, press ENTER or ESC.

To invoke option menu #2, press SHIFT+F9. You will see a list of options (described below). To select an option, press its first letter. To exit from option menu #2, press ENTER or ESC.

I wrote the built-in debugger primarily to help debug the Z-80 emulation, but it could also be useful to assembly language programmers. If you are familiar with the commands used by most TRS-80 debuggers, then you should feel right at home. If you enter the debugger accidentally, just press F7 or ESC to exit.

Here are the commands:

HDFORMAT.EXE

HDFORMAT

HARD/CMD

CLOCKSET/CMD

QUIET - Hides all messages unless an error occurs (this is useful if you run CLOCKSET/CMD as an AUTO command -- see below)

CLOCKSET (QUIET)

AUTO CLOCKSET (QUIET)

MOUSE/CMD

TRSREAD.EXE is an MS-DOS program that will read selected files from a TRS-80 virtual disk file or a real TRS-80 disk and transfer them to MS-DOS files. The TRSREAD command line looks like this:

TRSREAD [options] virtual_disk [files]

The [options] and [files] on the command line are optional. Possible options are:

For example, to look at the directory of SAMPLE.DSK, the command line would look like this:

TRSREAD SAMPLE

You don't actually have to use the -v option, because it is the default, and you also don't need to specify the .DSK extension. However, if you would prefer, you could also use this command line to accomplish the same thing:

TRSREAD -v SAMPLE.DSK

To extract all files from SAMPLE.DSK that begin with the letter S, including invisible and system files. the command line would look like this (notice the use of MS-DOS style wildcards):

TRSREAD -e-i-s SAMPLE S*.*

To extract the visible, non-system files LETTER1/TXT, LETTER2/TXT, and ADDRESS/TXT from SAMPLE.DSK, the command line would look like this:

TRSREAD -e SAMPLE LETTER1/TXT LETTER2/TXT ADDRESS/TXT

To extract all visible, non-system files from the TRS-80 disk in PC drive A:, the command line would look like this:

TRSREAD -e A: *.*

Note that when files are extracted from virtual disk files or TRS-80 disks, the resulting files are always copied into the current MS-DOS directory.

TRSWRITE.EXE is an MS-DOS program that will copy MS-DOS files into TRS-80 virtual disk files or onto real TRS-80 disks. The TRSWRITE command line looks like this:

TRSWRITE [option] virtual_disk file_or_wildcard

There is only one possible option:

-8 - Use 80 track disk in 80 track drive

For example, to copy the MS-DOS file LETTER1.TXT into the virtual disk file SAMPLE.DSK, the command line would look like this:

TRSWRITE SAMPLE LETTER1.TXT

To copy all files starting with B and with a .DOC extension onto the TRS-80 disk in drive A:, the command line would look like this:

TRSWRITE A: B*.DOC

To copy the files LETTER1.TXT, LETTER2.TXT, and ADDRESS.TXT into SAMPLE.DSK would require three command lines:

TRSWRITE SAMPLE LETTER1.TXT
TRSWRITE SAMPLE LETTER2.TXT
TRSWRITE SAMPLE ADDRESS.TXT

Note that the files to be copied must exist in the current MS-DOS directory.

I designed this emulator hard disk format back in 1997 for my MS-DOS based TRS-80 Model I/III emulator. I intended for it to be used by an emulator-based hard disk driver which communicated directly with the emulator using special hooks.

But it also worked surprisingly well for a hardware emulated hard drive and became the unoffical standard for TRS-80 emulated hard drives. The odd data structure comes about because it was derived from an earlier (no longer in use) disk image format.

My Windows TRS-80 emulator uses an updated version of this format (HDV version 2.0). But version 1.0 is still useful because of its simplicity: any sector position can be calculated using just the information in the header.

Each file starts with a 256 byte header, and sectors follow sequentially after.

Thanks to Tim Mann, Pete Cervasio, Andrew Quinn, and Frederic Vecoven for suggestions.