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CMP: Difference between revisions
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{| class="wikitable" style="float:right;clear:right;width:50%" | |||
{| class="wikitable" style="float:right;clear:right;width: | |||
!colspan="8"|Basic Info | !colspan="8"|Basic Info | ||
|+ | |+ | ||
Line 9: | Line 7: | ||
|'''Speed''' | |'''Speed''' | ||
|+ | |+ | ||
| | |[[Immediate]] | ||
|C9 | |C9 | ||
|2 bytes | |2 bytes* | ||
|2 cycles | |2 cycles* | ||
|+ | |+ | ||
| | |[[Absolute]] | ||
|CD | |CD | ||
|3 bytes | |3 bytes | ||
|4 cycles | |4 cycles* | ||
|+ | |+ | ||
| | |[[Absolute Long]] | ||
|CF | |CF | ||
|4 bytes | |4 bytes | ||
|5 cycles | |5 cycles* | ||
|+ | |+ | ||
| | |[[Direct Page Addressing|Direct Page]] | ||
|C5 | |C5 | ||
|2 bytes | |2 bytes | ||
|3 cycles | |3 cycles* | ||
|+ | |+ | ||
| | |[[Direct Page Indirect]] | ||
|D2 | |D2 | ||
|2 bytes | |2 bytes | ||
|5 cycles | |5 cycles* | ||
|+ | |+ | ||
| | |[[Direct Page Indirect Long]] | ||
|C7 | |C7 | ||
|2 bytes | |2 bytes | ||
|6 cycles | |6 cycles* | ||
|+ | |+ | ||
|absolute indexed by X | |absolute indexed by X | ||
|DD | |DD | ||
|3 bytes | |3 bytes | ||
|4 cycles | |4 cycles* | ||
|+ | |+ | ||
|absolute long indexed by X | |absolute long indexed by X | ||
|DF | |DF | ||
|4 bytes | |4 bytes | ||
|5 cycles | |5 cycles* | ||
|+ | |+ | ||
|absolute indexed by Y | |absolute indexed by Y | ||
|D9 | |D9 | ||
|3 bytes | |3 bytes | ||
|4 cycles | |4 cycles* | ||
|+ | |+ | ||
|direct page indexed by X | |direct page indexed by X | ||
|D5 | |D5 | ||
|2 bytes | |2 bytes | ||
|4 cycles | |4 cycles* | ||
|+ | |+ | ||
|direct page indexed indirect by X | |direct page indexed indirect by X | ||
|C1 | |C1 | ||
|2 bytes | |2 bytes | ||
|6 cycles | |6 cycles* | ||
|+ | |+ | ||
|direct page indirect indexed by Y | |direct page indirect indexed by Y | ||
|D1 | |D1 | ||
|2 bytes | |2 bytes | ||
|5 cycles | |5 cycles* | ||
|+ | |+ | ||
|direct page indirect long indexed by Y | |direct page indirect long indexed by Y | ||
|D7 | |D7 | ||
|2 bytes | |2 bytes | ||
|6 cycles | |6 cycles* | ||
|+ | |+ | ||
| | |[[Stack Relative]] | ||
|C3 | |C3 | ||
|2 bytes | |2 bytes | ||
|4 cycles | |4 cycles* | ||
|+ | |+ | ||
|stack relative indirect indexed by Y | |stack relative indirect indexed by Y | ||
|D3 | |D3 | ||
|2 bytes | |2 bytes | ||
|7 cycles | |7 cycles* | ||
|} | |} | ||
{| class="wikitable" style="float:right;clear:right;width:30%" | {| class="wikitable" style="float:right;clear:right;width:30%" | ||
!colspan="9"|Flags | !colspan="9"|Flags Affected | ||
|+ | |+ | ||
|N | |[[Negative Flag|N]] | ||
|V | |[[Overflow Flag|V]] | ||
|M | |[[M Flag|M]] | ||
|X | |[[X Flag|X]] | ||
|D | |[[Decimal Flag|D]] | ||
|I | |[[I Flag|I]] | ||
|Z | |[[Zero Flag|Z]] | ||
|C | |[[Carry Flag|C]] | ||
|+ | |+ | ||
| | | | ||
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| | | | ||
|} | |} | ||
'''CMP''' (Compare) is a 65x instruction that compares the value of the [[accumulator]] to something. Internally, this is done via a subtraction, but the difference is not stored anywhere. CMP only does unsigned comparisons. In [[immediate addressing]] only, CMP is a total of 3 bytes long when the accumulator is 16 bits wide. Unlike [[SBC]], the [[carry flag]] does not affect CMP. | |||
===== Cycle Penalties ===== | |||
* In all [[addressing modes]], CMP takes an extra cycle when the accumulator is 16 bits wide | |||
* In [[direct page addressing]] modes, CMP takes an extra cycle when the low byte of the [[direct page register]] is nonzero | |||
* In both [[Absolute Indexed]] and DP Indirect Indexed by Y, CMP takes an extra cycle if adding the index crosses a page boundary | |||
=== See Also === | === See Also === | ||
* [[CPX]] | * [[CPX]] | ||
* [[CPY]] | * [[CPY]] | ||
* [[CMP (Super FX)]] | |||
=== External Links === | === External Links === | ||
* [[Eyes & Lichty]] page on CMP: https://archive.org/details/0893037893ProgrammingThe65816/page/n471 | * [[Eyes & Lichty]] page 445, on CMP: https://archive.org/details/0893037893ProgrammingThe65816/page/n471 | ||
* [[Labiak]] page on CMP: https://archive.org/details/Programming_the_65816/page/ | * [[Labiak]] page 134 on CMP: https://archive.org/details/Programming_the_65816/page/n144 | ||
* [[MCS6500 Manual]] page on CMP: https://archive.org/details/mos_microcomputers_programming_manual/page/n60 | * [[MCS6500 Manual]] page 45 on CMP: https://archive.org/details/mos_microcomputers_programming_manual/page/n60 | ||
* [[Carr]] page on CMP: https://archive.org/details/6502UsersManual/page/n268 | * [[Carr]] page 255 on CMP: https://archive.org/details/6502UsersManual/page/n268 | ||
* [[Leventhal]] page on CMP: https://archive.org/details/6502-assembly-language-programming/page/n105 | * [[Leventhal]] page 3-56 on CMP: https://archive.org/details/6502-assembly-language-programming/page/n105 | ||
* snes9x implementation of CMP: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L304 | * snes9x implementation of CMP: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L304 | ||
* undisbeliever on CMP: https://undisbeliever.net/snesdev/65816-opcodes.html#cmp-compare-accumulator-with-memory | * undisbeliever on CMP: https://undisbeliever.net/snesdev/65816-opcodes.html#cmp-compare-accumulator-with-memory |
Latest revision as of 06:15, 6 December 2023
Basic Info | |||||||
---|---|---|---|---|---|---|---|
Addressing Mode | Opcode | Length | Speed | ||||
Immediate | C9 | 2 bytes* | 2 cycles* | ||||
Absolute | CD | 3 bytes | 4 cycles* | ||||
Absolute Long | CF | 4 bytes | 5 cycles* | ||||
Direct Page | C5 | 2 bytes | 3 cycles* | ||||
Direct Page Indirect | D2 | 2 bytes | 5 cycles* | ||||
Direct Page Indirect Long | C7 | 2 bytes | 6 cycles* | ||||
absolute indexed by X | DD | 3 bytes | 4 cycles* | ||||
absolute long indexed by X | DF | 4 bytes | 5 cycles* | ||||
absolute indexed by Y | D9 | 3 bytes | 4 cycles* | ||||
direct page indexed by X | D5 | 2 bytes | 4 cycles* | ||||
direct page indexed indirect by X | C1 | 2 bytes | 6 cycles* | ||||
direct page indirect indexed by Y | D1 | 2 bytes | 5 cycles* | ||||
direct page indirect long indexed by Y | D7 | 2 bytes | 6 cycles* | ||||
Stack Relative | C3 | 2 bytes | 4 cycles* | ||||
stack relative indirect indexed by Y | D3 | 2 bytes | 7 cycles* |
Flags Affected | ||||||||
---|---|---|---|---|---|---|---|---|
N | V | M | X | D | I | Z | C | |
. | . | . | . | . |
CMP (Compare) is a 65x instruction that compares the value of the accumulator to something. Internally, this is done via a subtraction, but the difference is not stored anywhere. CMP only does unsigned comparisons. In immediate addressing only, CMP is a total of 3 bytes long when the accumulator is 16 bits wide. Unlike SBC, the carry flag does not affect CMP.
Cycle Penalties
- In all addressing modes, CMP takes an extra cycle when the accumulator is 16 bits wide
- In direct page addressing modes, CMP takes an extra cycle when the low byte of the direct page register is nonzero
- In both Absolute Indexed and DP Indirect Indexed by Y, CMP takes an extra cycle if adding the index crosses a page boundary
See Also
External Links
- Eyes & Lichty page 445, on CMP: https://archive.org/details/0893037893ProgrammingThe65816/page/n471
- Labiak page 134 on CMP: https://archive.org/details/Programming_the_65816/page/n144
- MCS6500 Manual page 45 on CMP: https://archive.org/details/mos_microcomputers_programming_manual/page/n60
- Carr page 255 on CMP: https://archive.org/details/6502UsersManual/page/n268
- Leventhal page 3-56 on CMP: https://archive.org/details/6502-assembly-language-programming/page/n105
- snes9x implementation of CMP: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L304
- undisbeliever on CMP: https://undisbeliever.net/snesdev/65816-opcodes.html#cmp-compare-accumulator-with-memory