Difference between revisions of "Launching and Terminating Assembly Programs Commodore 64"
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(Created page with "==Synopsis== In it's default state, the Commodore 64 is executing a Microsoft BASIC interactive environment. When you run SYS 49152, this begins execution of assembly code st...") |
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==Assembly== | ==Assembly== | ||
<syntaxhighlight lang="nasm"> | <syntaxhighlight lang="nasm"> | ||
| − | save: | + | save: C000: |
PHP C000: 08 (8) | PHP C000: 08 (8) | ||
PHA C001: 48 (72) | PHA C001: 48 (72) | ||
| Line 13: | Line 13: | ||
TYA C004: 98 (152) | TYA C004: 98 (152) | ||
PHA C005: 48 (72) | PHA C005: 48 (72) | ||
| − | restore: C006: | + | restore:C006: |
PLA C006: 68 (104) | PLA C006: 68 (104) | ||
TAY C007: A8 (168) | TAY C007: A8 (168) | ||
Latest revision as of 03:53, 3 November 2021
Synopsis
In it's default state, the Commodore 64 is executing a Microsoft BASIC interactive environment. When you run SYS 49152, this begins execution of assembly code starting from $C000. If you intend to return back to the BASIC interpreter without doing a hard reset, you must push and pop all the CPU registers.
PHP first pushes processor flags to stack. PHA then pushes A to the stack. There is no opcode for pushing X or Y, so they must be transferred to A. To return to the BASIC interpreter, these must be restored in opposite order and then returned using RTS.
Assembly
save: C000:
PHP C000: 08 (8)
PHA C001: 48 (72)
TXA C002: 8A (138)
PHA C003: 48 (72)
TYA C004: 98 (152)
PHA C005: 48 (72)
restore:C006:
PLA C006: 68 (104)
TAY C007: A8 (168)
PLA C008: 68 (104)
TAX C009: AA (170)
PLA C00A: 68 (104)
PLP C00B: 28 (40)
RTS C00C: 60 (96)
