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ORA: Difference between revisions
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'''ORA''' is a 65x instruction that performs a logical OR and stores the disjunction in the | '''ORA''' is a 65x instruction that performs a logical OR between the datum at the effective address and the [[accumulator]] and stores the disjunction in the accumulator. The size of the accumulator determines whether 8 or 16 bits are ORed. | ||
==== Syntax ==== | ==== Syntax ==== | ||
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</pre> | </pre> | ||
==== Cycle Penalties ==== | |||
* In all [[addressing modes]], ORA takes one extra cycle when the accumulator is 16 bits wide. | * 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. | * In [[direct page addressing]] modes, ORA takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | ||
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* [[EOR]] | * [[EOR]] | ||
* [[OR (Super FX)]] | * [[OR (Super FX)]] | ||
* [[XOR (Super FX)]] | |||
=== External Links === | === External Links === | ||
* [[Eyes & Lichty]] | * [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/471 page 471] on ORA | ||
* [[Labiak]] | * [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n166 page 156] on ORA | ||
* [[MCS6500 Manual]] | * 2.2.4.2 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n36 page 21] on ORA | ||
* [[Carr]] | * [[Carr]], [https://archive.org/details/6502UsersManual/page/n279 page 266] on ORA | ||
* [[Leventhal]] | * [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n128 page 3-79] on ORA | ||
* snes9x implementation of ORA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L917 | * 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 | * 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 | |||
* Bruce, Clark. http://www.6502.org/tutorials/65c816opcodes.html#6.1.2.1 | |||
[[Category:ASM]] | [[Category:ASM]] | ||
[[Category:Group One Instructions]] | [[Category:Group One Instructions]] | ||
[[Category:Inherited from 6502]] | [[Category:Inherited from 6502]] | ||
Latest revision as of 17:46, 23 August 2024
| 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 |
| N | . | . | . | . | . | Z | . |
ORA is a 65x instruction that performs a logical OR between the datum at the effective address and the accumulator and stores the disjunction in the accumulator. The size of the accumulator determines whether 8 or 16 bits are ORed.
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
- Labiak, page 156 on ORA
- 2.2.4.2 on MCS6500 Manual, page 21 on ORA
- Carr, page 266 on ORA
- Leventhal, page 3-79 on ORA
- 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
- Bruce, Clark. http://www.6502.org/tutorials/65c816opcodes.html#6.1.2.1