Appendix 1 — Directive Reference

Atom has two directive groups. Bare assembler directives control assembly. % directives control source preparation and are removed before assembly. Both groups are case-insensitive.

Assembler directives

Directive	Syntax	Effect	Hosts
EQU	NAME EQU EXPR or NAME: EQU EXPR	Declares one resolved constant without changing private scope	Desktop, CP/M
ORG	ORG EXPR	Sets the logical output cursor; emits no byte	Desktop, CP/M
DB	DB ITEM[,ITEM…]	Emits low bytes from expressions and decoded double-quoted strings	Desktop, CP/M
DW	DW EXPR[,EXPR…]	Emits little-endian words	Desktop, CP/M
DS	DS COUNT	Reserves uninitialised bytes and advances the cursor	Desktop, CP/M
DS	DS COUNT,FILL	Emits COUNT initialized fill bytes	Desktop, CP/M
ALIGN	ALIGN BOUNDARY	Emits zeros to the next address divisible by a positive boundary	Desktop, CP/M
INCBIN	INCBIN "PATH"	Emits one complete confined host binary snapshot	Desktop
CSTR	CSTR "TEXT"	Emits decoded bytes followed by zero	Desktop, CP/M
PSTR	PSTR "TEXT"	Emits a decoded-byte count followed by the bytes	Desktop, CP/M
ISTR	ISTR "TEXT"	Sets bit 7 on the final decoded byte; empty text emits nothing	Desktop, CP/M

Dotted directive aliases are invalid. A leading period begins a private symbol:

ORG 4000H       ; ASSEMBLER DIRECTIVE
.ORG:           ; PRIVATE LABEL

EQU, ORG, DS, and ALIGN require already resolved expressions. DB and DW accept Atom's restricted forward affine form.

Preprocessor directives

Directive	Syntax	Effect	Hosts
%DEFINE	%DEFINE NAME VALUE	Binds one immutable 16-bit host value in the entry header	Desktop
%INCLUDE	%INCLUDE "PATH"	Adds one import-once dependency edge from a leading part header	Desktop, CP/M
%IF	%IF VALUE	Selects the following branch when the value is non-zero	Desktop
%ELSE	%ELSE	Selects the alternate branch	Desktop
%ENDIF	%ENDIF	Closes the current host conditional	Desktop

%DEFINE performs no source substitution and declares no assembler symbol. Dependencies may test entry definitions but may not add definitions. Body conditionals may select ordinary source but cannot add includes or definitions.

The desktop preprocessor replaces directive and inactive lines with spaces while preserving CR and LF bytes. The CP/M provider validates leading %INCLUDE directives and turns them into assembler comments. Both retain the original line and byte positions for diagnostics.