Model I, III, and 4 ROM Explained - Full

Introduction

These are interactive disassemblies of the Model I and III Level II BASIC ROMs and the Model 4 ROM. Use the controls below to select the ROM version you want to view and choose which columns to display.

The ROM had to fit in one continuous block from 0000H to its end, and every routine had to be wedged into that space. Expect a lot of JP/JR jumps.
Z-80 instructions don't include every conceivable operation (e.g. there is no LD BC,SP), so the ROM does a great deal of register-pair swapping.

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Col 2 Contents Show Z-80 Mnemonic with Hex Show Z-80 Opcodes Show Labels Show 8080 Mnemonic

Comments Show Section Introductory Notes Show Section Description Notes Show Interlineated Reference Notes Show Original Source Code Routine Notes Show TRS-80 Description of each instruction Show Original Source Code Comment

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Model I, III, and 4 ROMs Disassembled