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	Node, CP/M
ORG	ORG EXPR	Sets the logical output cursor; emits no byte	Node, CP/M
DB	DB ITEM[,ITEM…]	Emits low bytes from expressions and decoded double-quoted strings	Node, CP/M
DW	DW EXPR[,EXPR…]	Emits little-endian words	Node, CP/M
DS	DS COUNT	Reserves uninitialised bytes and advances the cursor	Node, CP/M
DS	DS COUNT,FILL	Emits COUNT initialized fill bytes	Node, CP/M
ALIGN	ALIGN BOUNDARY	Emits zeros to the next address divisible by a positive boundary	Node, CP/M
INCBIN	INCBIN "PATH"[,COUNT]	Emits the first COUNT bytes of a binary file, or the whole file on Node when COUNT is omitted	Node, CP/M
CSTR	CSTR "TEXT"	Emits decoded bytes followed by zero	Node, CP/M
PSTR	PSTR "TEXT"	Emits a decoded-byte count followed by the bytes	Node, CP/M
ISTR	ISTR "TEXT"	Sets bit 7 on the final decoded byte; empty text emits nothing	Node, 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. The INCBIN count is a numeric literal. CP/M requires it and uses a current-drive 8.3 name for PATH.

Preprocessor directives

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

%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 Node preprocessor replaces directive and inactive lines with spaces while preserving CR and LF bytes. The CP/M preprocessor turns each directive into an assembler comment and masks inactive lines. Both retain the original line and byte positions for diagnostics.

On CP/M, %DEFINE lines must come before any %INCLUDE or conditional directive, with at most 32 definitions. Conditionals nest up to 16 levels.