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ORA
From SnesLab
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Immediate | 09 | 2/3 bytes | 2 cycles* | ||||
| Absolute | 0D | 3 bytes | 4 cycles* | ||||
| Absolute Long | 0F | 4 bytes | 5 cycles* | ||||
| Direct Page | 05 | 2 bytes | 3 cycles* | ||||
| Direct Page Indirect | 12 | 2 bytes | 5 cycles* | ||||
| Direct Page Indirect Long | 07 | 2 bytes | 6 cycles* | ||||
| Absolute Indexed by X | 1D | 3 bytes | 4 cycles* | ||||
| Absolute Long Indexed by X | 1F | 4 bytes | 5 cycles* | ||||
| Absolute Indexed by Y | 19 | 3 bytes | 4 cycles* | ||||
| Direct Page Indexed by X | 15 | 2 bytes | 4 cycles* | ||||
| Direct Page Indexed Indirect by X | 01 | 2 bytes | 6 cycles* | ||||
| Direct Page Indirect Indexed by Y | 11 | 2 bytes | 5 cycles* | ||||
| Direct Page Indirect Long Indexed by Y | 17 | 2 bytes | 6 cycles* | ||||
| Stack Relative | 03 | 2 bytes | 4 cycles* | ||||
| Stack Relative Indirect Indexed by Y | 13 | 2 bytes | 7 cycles* | ||||
| Flags Affected | |||||||
|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C |
| . | . | . | . | . | . | ||
ORA is a 65x instruction that performs a logical OR and stores the disjunction in the accumulator.
Syntax
ORA #const ORA addr ORA long ORA dp ORA (dp) ORA [dp] ORA addr, X ORA long, X ORA addr, Y ORA dp, X ORA (dp, X) ORA (dp), Y ORA [dp], Y ORA sr, S ORA (sr, S), Y
Cycle Penalties
- In all addressing modes, ORA takes one extra cycle when the accumulator is 16 bits wide.
- In direct page addressing modes, ORA takes another extra cycle if the low byte of the direct page register is nonzero.
See Also
External Links
- Eyes & Lichty page 471, on ORA: https://archive.org/details/0893037893ProgrammingThe65816/page/471
- Labiak page 156 on ORA: https://archive.org/details/Programming_the_65816/page/n166
- MCS6500 Manual page 21 on ORA: https://archive.org/details/mos_microcomputers_programming_manual/page/n36
- Carr page 266 on ORA: https://archive.org/details/6502UsersManual/page/n279
- Leventhal page 3-79 on ORA: https://archive.org/details/6502-assembly-language-programming/page/n128
- snes9x implementation of ORA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L917
- undisbeliever on ORA: https://undisbeliever.net/snesdev/65816-opcodes.html#ora-or-accumulator-with-memory
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#ORA