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ORA
From SnesLab
Basic Info | |||||||
---|---|---|---|---|---|---|---|
Addressing Mode | Opcode | Length | Speed | ||||
Immediate | 09 | 2 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 result in the accumulator.
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/n497
- 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