Introduction

Atom is a single-pass Z80 assembler. It reads one or more .asm files and produces Z80 machine code.

This book defines the source language: instructions, symbols, expressions, directives and source composition. Reference tables follow the chapters. Installation and commands are covered by the Node guide and CP/M guide.

The intended reader

The manual assumes that you can read Z80 assembly and recognise its registers, instructions, flags, stack and addressing forms. Atom Book 2 — Z80 Programming provides a from-zero introduction to the processor.

Programmers coming from another assembler should begin with Chapters 1 and 2. The two source conventions most likely to differ are visible immediately: assembler directives are bare words such as ORG and DB, while a leading period marks a private symbol such as .LOOP.

Assembly and source preparation

Atom separates assembly from operations that require access to files. The assembler handles symbols, expressions, instructions, directives and forward references in a single pass through the prepared source.

Before that pass, the host's source-preparation stage resolves %INCLUDE, %DEFINE, %IF, %ELSE and %ENDIF and locates each file named by INCBIN. Node and CP/M both provide these facilities, with different path rules and limits. After assembly, each host writes the requested output. %DEFINE controls preprocessing while EQU declares a value that assembly expressions can use.

The first chapter explains a small program and the bytes it produces.