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CPY
From SnesLab
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Immediate | C0 | 2/3 bytes | 2 cycles* | ||||
| Absolute | CC | 3 bytes | 4 cycles* | ||||
| Direct Page | C4 | 2 bytes | 3 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| . | . | . | . | . | ||||
CPY (Compare Y) is a 65x instruction that compares the value of the Y index register. Internally, this is done via a subtraction, but the difference is not stored anywhere. Thus, the purpose of CPY is to setup the flags. The index register Y is the minuend. The contents at the effective address (when not using immediate data) and the Y index register both remain unchanged.
CPY assumes its operands are unsigned.
Syntax
CPY #const CPY addr CPY dp
Cycle Penalties
TODO
See Also
External Links
- Eyes & Lichty page 450, on CPY: https://archive.org/details/0893037893ProgrammingThe65816/page/450
- Labiak page 137 on CPY: https://archive.org/details/Programming_the_65816/page/n147
- MCS6500 Manual page 99 on CPY: https://archive.org/details/mos_microcomputers_programming_manual/page/n117
- Carr page 257 on CPY: https://archive.org/details/6502UsersManual/page/n270
- Leventhal page 3-59 on CPY: https://archive.org/details/6502-assembly-language-programming/page/n108
- snes9x implementation of CPY: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L442
- undisbeliever on CPY: https://undisbeliever.net/snesdev/65816-opcodes.html#cpy-compare-index-register-y-with-memory
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#CPY