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STA: Difference between revisions
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|4 cycles* | |4 cycles* | ||
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| | |[[Absolute Long Indexed by X]] | ||
|9F | |9F | ||
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|4 cycles* | |4 cycles* | ||
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| | |[[Direct Page Indexed by X]] | ||
|95 | |95 | ||
|2 bytes | |2 bytes | ||
|4 cycles* | |4 cycles* | ||
|+ | |+ | ||
| | |[[Direct Page Indexed Indirect by X]] | ||
|81 | |81 | ||
|2 bytes | |2 bytes | ||
|6 cycles* | |6 cycles* | ||
|+ | |+ | ||
| | |[[Direct Page Indirect Indexed by Y]] | ||
|91 | |91 | ||
|2 bytes | |2 bytes | ||
|5 cycles* | |5 cycles* | ||
|+ | |+ | ||
| | |[[Direct Page Indirect Long Indexed by Y]] | ||
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'''STA''' (Store Accumulator) is a 65x instruction that stores the value of the [[accumulator]]. If the accumulator is 16 bits wide, its low byte is stored at the effective address and its high byte is stored at the effective address plus one. | '''STA''' (Store Accumulator) is a 65x instruction that stores the value of the [[accumulator]]. If the accumulator is 16 bits wide, its low byte is stored at the effective address and its high byte is stored at the effective address plus one. | ||
===== Cycle Penalties | No flags are affected. | ||
==== Syntax ==== | |||
<pre> | |||
STA addr | |||
STA long | |||
STA dp | |||
STA (dp) | |||
STA [dp] | |||
STA addr, X | |||
STA long, X | |||
STA addr, Y | |||
STA dp, X | |||
STA (dp, X) | |||
STA (dp), Y | |||
STA [dp], Y | |||
STA sr, S | |||
STA (sr, S), Y | |||
</pre> | |||
If you are trying to store zero somewhere, consider [[STZ]] instead. | |||
==== Cycle Penalties ==== | |||
* In all [[addressing modes]], STA takes one extra cycle when the accumulator is 16 bits wide. | * In all [[addressing modes]], STA takes one extra cycle when the accumulator is 16 bits wide. | ||
* In [[direct page addressing]] modes, STA takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | * In [[direct page addressing]] modes, STA takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | ||
| Line 110: | Line 132: | ||
* [[STX]] | * [[STX]] | ||
* [[STY]] | * [[STY]] | ||
=== External Links === | === External Links === | ||
* [[Eyes & Lichty]] | * [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/503 page 503] on STA | ||
* [[Labiak]] | * [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n194 page 184] on STA | ||
* [[MCS6500 Manual]] | * 2.1.2 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n20 page 5] on STA | ||
* [[Carr]] | * [[Carr]], [https://archive.org/details/6502UsersManual/page/n286 page 273] on STA | ||
* [[Leventhal]] | * [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n145 page 3-96] on STA | ||
* snes9x implementation of STA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1219 | * snes9x implementation of STA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1219 | ||
* undisbeliever on STA: https://undisbeliever.net/snesdev/65816-opcodes.html#sta-store-accumulator-to-memory | * undisbeliever on STA: https://undisbeliever.net/snesdev/65816-opcodes.html#sta-store-accumulator-to-memory | ||
* Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#STA | |||
[[Category:ASM]] | [[Category:ASM]] | ||
Latest revision as of 06:37, 22 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Absolute | 8D | 3 bytes | 4 cycles* | ||||
| Absolute Long | 8F | 4 bytes | 5 cycles* | ||||
| Direct Page | 85 | 2 bytes | 3 cycles* | ||||
| Direct Page Indirect | 92 | 2 bytes | 5 cycles* | ||||
| Direct Page Indirect Long | 87 | 2 bytes | 6 cycles* | ||||
| Absolute Indexed by X | 9D | 3 bytes | 4 cycles* | ||||
| Absolute Long Indexed by X | 9F | 4 bytes | 5 cycles* | ||||
| Absolute Indexed by Y | 99 | 3 bytes | 4 cycles* | ||||
| Direct Page Indexed by X | 95 | 2 bytes | 4 cycles* | ||||
| Direct Page Indexed Indirect by X | 81 | 2 bytes | 6 cycles* | ||||
| Direct Page Indirect Indexed by Y | 91 | 2 bytes | 5 cycles* | ||||
| Direct Page Indirect Long Indexed by Y | 97 | 2 bytes | 6 cycles* | ||||
| Stack Relative | 83 | 2 bytes | 4 cycles* | ||||
| Stack Relative Indirect Indexed by Y | 93 | 2 bytes | 7 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| . | . | . | . | . | . | . | . | |
STA (Store Accumulator) is a 65x instruction that stores the value of the accumulator. If the accumulator is 16 bits wide, its low byte is stored at the effective address and its high byte is stored at the effective address plus one.
No flags are affected.
Syntax
STA addr STA long STA dp STA (dp) STA [dp] STA addr, X STA long, X STA addr, Y STA dp, X STA (dp, X) STA (dp), Y STA [dp], Y STA sr, S STA (sr, S), Y
If you are trying to store zero somewhere, consider STZ instead.
Cycle Penalties
- In all addressing modes, STA takes one extra cycle when the accumulator is 16 bits wide.
- In direct page addressing modes, STA takes another extra cycle if the low byte of the direct page register is nonzero.
See Also
External Links
- Eyes & Lichty, page 503 on STA
- Labiak, page 184 on STA
- 2.1.2 on MCS6500 Manual, page 5 on STA
- Carr, page 273 on STA
- Leventhal, page 3-96 on STA
- snes9x implementation of STA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1219
- undisbeliever on STA: https://undisbeliever.net/snesdev/65816-opcodes.html#sta-store-accumulator-to-memory
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#STA