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EOR: Difference between revisions
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'''EOR''' is a 65x instruction that performs | '''EOR''' is a 65x instruction that performs a bitwise [https://mathworld.wolfram.com/XOR.html exclusive or] between its operand and the accumulator. The sum is stored in the [[accumulator]]. The size of the accumulator determines whether 8 or 16 bits are EORed. | ||
==== Syntax ==== | ==== Syntax ==== | ||
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</pre> | </pre> | ||
One example usage of EOR is to flip all the bits of the accumulator | One example usage of EOR is to flip all the bits of the accumulator:<sup>[10]</sup> | ||
<pre> | |||
EOR #$FFFF | |||
</pre> | |||
==== Cycle Penalties ==== | |||
* In all [[addressing modes]], EOR takes one extra cycle when the accumulator is 16 bits wide. | * In all [[addressing modes]], EOR takes one extra cycle when the accumulator is 16 bits wide. | ||
* In [[direct page addressing]] modes, EOR takes one additional cycle if the low byte of the [[direct page register]] is nonzero. | * In [[direct page addressing]] modes, EOR takes one additional cycle if the low byte of the [[direct page register]] is nonzero. | ||
Latest revision as of 17:46, 23 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Immediate | 49 | 2/3 bytes | 2 cycles* | ||||
| Absolute | 4D | 3 bytes | 4 cycles* | ||||
| Absolute Long | 4F | 4 bytes | 5 cycles* | ||||
| Direct Page | 45 | 2 bytes | 3 cycles* | ||||
| Direct Page Indirect | 52 | 2 bytes | 5 cycles* | ||||
| Direct Page Indirect Long | 47 | 2 bytes | 6 cycles* | ||||
| Absolute Indexed by X | 5D | 3 bytes | 4 cycles* | ||||
| Absolute Long Indexed by X | 5F | 4 bytes | 5 cycles* | ||||
| Absolute Indexed by Y | 59 | 3 bytes | 4 cycles* | ||||
| Direct Page Indexed by X | 55 | 2 bytes | 4 cycles* | ||||
| Direct Page Indexed Indirect by X | 41 | 2 bytes | 6 cycles* | ||||
| Direct Page Indirect Indexed by Y | 51 | 2 bytes | 5 cycles* | ||||
| Direct Page Indirect Long Indexed by Y | 57 | 2 bytes | 6 cycles* | ||||
| Stack Relative | 43 | 2 bytes | 4 cycles* | ||||
| Stack Relative Indirect Indexed by Y | 53 | 2 bytes | 7 cycles* | ||||
| Flags Affected | |||||||
|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C |
| N | . | . | . | . | . | Z | . |
EOR is a 65x instruction that performs a bitwise exclusive or between its operand and the accumulator. The sum is stored in the accumulator. The size of the accumulator determines whether 8 or 16 bits are EORed.
Syntax
EOR #const EOR addr EOR long EOR dp EOR (dp) EOR [dp] EOR addr, X EOR long, X EOR addr, Y EOR dp, X EOR (dp, X) EOR (dp), Y EOR [dp], Y EOR sr, S EOR (sr, S), Y
One example usage of EOR is to flip all the bits of the accumulator:[10]
EOR #$FFFF
Cycle Penalties
- In all addressing modes, EOR takes one extra cycle when the accumulator is 16 bits wide.
- In direct page addressing modes, EOR takes one additional cycle if the low byte of the direct page register is nonzero.
- In both Absolute Indexed and DP Indirect Indexed, Y admodes, EOR takes an extra cycle if adding the index crosses a page boundary.
See Also
External Links
- Eyes & Lichty, page 454 on EOR
- Labiak, page 141 on EOR
- 2.2.4.3 on MCS6500 Manual, page 21 on EOR
- Carr, page 259 on EOR
- Leventhal, page 3-63 on EOR
- snes9x implementation of EOR: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L533
- undisbeliever on EOR: https://undisbeliever.net/snesdev/65816-opcodes.html#eor-exclusive-or-accumulator-with-memory
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#EOR
- Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.1.2.1
- Carr, page 260