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LDX: Difference between revisions
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'''LDX''' (Load X) is a 65x instruction that loads the [[X index register]]. In [[immediate addressing]] only, LDX is a total of 3 bytes long when the index registers are 16 bits wide. | '''LDX''' (Load X) is a 65x instruction that loads a value into the [[X index register]]. In [[immediate addressing]] only, LDX is a total of 3 bytes long when the index registers are 16 bits wide. | ||
==== Syntax ==== | ==== Syntax ==== | ||
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</pre> | </pre> | ||
==== Cycle Penalties ==== | |||
* In [[direct page addressing]] modes, LDX takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | * In [[direct page addressing]] modes, LDX takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | ||
* | * | ||
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* [[LDA]] | * [[LDA]] | ||
* [[LDY]] | * [[LDY]] | ||
* [[TAX]] | |||
* [[TYX]] | |||
* [[TSX]] | |||
=== External Links === | === External Links === | ||
* [[Eyes & Lichty]] | * [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/463 page 463] on LDX | ||
* [[Labiak]] | * [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n160 page 150] on LDX | ||
* [[MCS6500 Manual]] | * 7.0 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n114 page 96] on LDX | ||
* https://archive.org/details/mos_microcomputers_programming_manual/page/n219, lbid. | * [https://archive.org/details/mos_microcomputers_programming_manual/page/n219 B-18], lbid. | ||
* [[Carr]] | * [[Carr]], [https://archive.org/details/6502UsersManual/page/n277 page 264] on LDX | ||
* [[Leventhal]] | * [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n121 page 3-72] on LDX | ||
* snes9x implementation of LDX: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L772 | * snes9x implementation of LDX: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L772 | ||
* undisbeliever on LDX: https://undisbeliever.net/snesdev/65816-opcodes.html#ldx-load-index-register-x-from-memory | * undisbeliever on LDX: https://undisbeliever.net/snesdev/65816-opcodes.html#ldx-load-index-register-x-from-memory | ||
* Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#LDX | |||
[[Category:ASM]] | [[Category:ASM]] | ||
Latest revision as of 06:38, 22 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Immediate | A2 | 2/3 bytes | 2 cycles* | ||||
| Absolute | AE | 3 bytes | 4 cycles* | ||||
| Direct Page | A6 | 2 bytes | 3 cycles* | ||||
| Absolute Indexed by Y | BE | 3 bytes | 4 cycles* | ||||
| Direct Page Indexed by Y | B6 | 2 bytes | 4 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| N | . | . | . | . | . | Z | . | |
LDX (Load X) is a 65x instruction that loads a value into the X index register. In immediate addressing only, LDX is a total of 3 bytes long when the index registers are 16 bits wide.
Syntax
LDX #const LDX addr LDX dp LDX addr, Y LDX dp, Y
Cycle Penalties
- In direct page addressing modes, LDX takes another extra cycle if the low byte of the direct page register is nonzero.
See Also
External Links
- Eyes & Lichty, page 463 on LDX
- Labiak, page 150 on LDX
- 7.0 on MCS6500 Manual, page 96 on LDX
- B-18, lbid.
- Carr, page 264 on LDX
- Leventhal, page 3-72 on LDX
- snes9x implementation of LDX: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L772
- undisbeliever on LDX: https://undisbeliever.net/snesdev/65816-opcodes.html#ldx-load-index-register-x-from-memory
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#LDX