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STX: Difference between revisions
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'''STX''' (Store X) is a 65x instruction that stores the value of the [[X index register]]. | '''STX''' (Store X) is a 65x instruction that stores the value of the [[X index register]]. If X is 16-bit, its high byte is stored to the effective address plus one. | ||
===== Cycle Penalties | No flags are affected. | ||
==== Syntax ==== | |||
<pre> | |||
STX addr | |||
STX dp | |||
STX dp, Y | |||
</pre> | |||
==== Cycle Penalties ==== | |||
* STX takes one additional cycle when the index registers are 16 bits wide, in all [[addressing modes]]. | * STX takes one additional cycle when the index registers are 16 bits wide, in all [[addressing modes]]. | ||
* In both [[direct page addressing]] modes only, STX takes another additional cycle if the low byte of the [[direct page register]] is nonzero. | * In both [[direct page addressing]] modes only, STX takes another additional cycle if the low byte of the [[direct page register]] is nonzero. | ||
| Line 56: | Line 65: | ||
* [[STY]] | * [[STY]] | ||
* [[STZ]] | * [[STZ]] | ||
* [[TXA]] | |||
* [[TXY]] | |||
* [[TXS]] | |||
=== External Links === | === External Links === | ||
* [[Eyes & Lichty]] | * [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/505 page 505], on STX | ||
* [[Labiak]] | * [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n196 page 186] on STX | ||
* [[MCS6500 Manual]] | * 7.2 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n115 page 97] on STX | ||
* [[Carr]] | * [[Carr]], [https://archive.org/details/6502UsersManual/page/n287 page 274] on STX | ||
* [[Leventhal]] | * [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n146 page 3-97] on STX | ||
* snes9x implementation of STX: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1287 | * snes9x implementation of STX: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1287 | ||
* undisbeliever on STX: https://undisbeliever.net/snesdev/65816-opcodes.html#stx-store-index-register-x-to-memory | * undisbeliever on STX: https://undisbeliever.net/snesdev/65816-opcodes.html#stx-store-index-register-x-to-memory | ||
* Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#STX | |||
[[Category:ASM]] | [[Category:ASM]] | ||
Latest revision as of 06:41, 22 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Absolute | 8E | 3 bytes | 4 cycles* | ||||
| Direct Page | 86 | 2 bytes | 3 cycles* | ||||
| Direct Page Indexed by Y | 96 | 2 bytes | 4 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| . | . | . | . | . | . | . | . | |
STX (Store X) is a 65x instruction that stores the value of the X index register. If X is 16-bit, its high byte is stored to the effective address plus one.
No flags are affected.
Syntax
STX addr STX dp STX dp, Y
Cycle Penalties
- STX takes one additional cycle when the index registers are 16 bits wide, in all addressing modes.
- In both direct page addressing modes only, STX takes another additional cycle if the low byte of the direct page register is nonzero.
See Also
External Links
- Eyes & Lichty, page 505, on STX
- Labiak, page 186 on STX
- 7.2 on MCS6500 Manual, page 97 on STX
- Carr, page 274 on STX
- Leventhal, page 3-97 on STX
- snes9x implementation of STX: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1287
- undisbeliever on STX: https://undisbeliever.net/snesdev/65816-opcodes.html#stx-store-index-register-x-to-memory
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#STX