Debug80 Docs

Atom Appendices04

Appendix 4 — Built-in Functions ​

Atom has two byte-selection functions. Both are case-insensitive and run at assembly time.

LOW(EXPR) ​

LOW returns bits 0 through 7:

text
LOW(VALUE) = VALUE & $FF
asm
ADDRESS EQU 0C432H
DB LOW(ADDRESS)       ; EMITS $32

HIGH(EXPR) ​

HIGH returns bits 8 through 15:

text
HIGH(VALUE) = (VALUE >> 8) & $FF
asm
ADDRESS EQU 0C432H
DB HIGH(ADDRESS)      ; EMITS $C4

Forward use ​

Each function may wrap one forward affine expression:

asm
DB LOW(TARGET+2),HIGH(TARGET+2)

The function must be the outermost operation. A further operation such as LOW(TARGET)+1 is rejected. Relative branches and IX/IY displacements require their own resolution-time range calculations and cannot use a forward byte function.

LOW and HIGH are ordinary legal symbol names when they are not followed by an opening parenthesis.