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LDY: Difference between revisions
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'''LDY''' (Load Y) is a 65x instruction that loads the [[Y index register]]. In [[immediate addressing]] only, LDY takes a total of 3 bytes when the index registers are 16 bits wide. | '''LDY''' (Load Y) is a 65x instruction that loads a value into the [[Y index register]]. In [[immediate addressing]] only, LDY takes a total of 3 bytes when the index registers are 16 bits wide. | ||
==== Syntax ==== | ==== Syntax ==== | ||
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</pre> | </pre> | ||
==== Cycle Penalties ==== | |||
* In [[direct page addressing]] modes, LDY takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | * In [[direct page addressing]] modes, LDY takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | ||
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* [[LDA]] | * [[LDA]] | ||
* [[LDX]] | * [[LDX]] | ||
* [[TAY]] | |||
* [[TXY]] | |||
=== External Links === | === External Links === | ||
* [[Eyes & Lichty]] | * [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/n490 page 464] on LDY | ||
* [[Labiak]] | * [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n161 page 151] on LDY | ||
* [[MCS6500 Manual]] | * 7.1 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n114 page 96] on LDY | ||
* [[Carr]] | * [[Carr]], [https://archive.org/details/6502UsersManual/page/n277 page 264] on LDY | ||
* [[Leventhal]] | * [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n123 page 3-74] on LDY | ||
* snes9x implementation of LDY: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L817 | * snes9x implementation of LDY: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L817 | ||
* undisbeliever on LDY: https://undisbeliever.net/snesdev/65816-opcodes.html#ldy-load-index-register-y-from-memory | * undisbeliever on LDY: https://undisbeliever.net/snesdev/65816-opcodes.html#ldy-load-index-register-y-from-memory | ||
* Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#LDY | |||
[[Category:ASM]] | [[Category:ASM]] | ||
Latest revision as of 06:32, 22 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Immediate | A0 | 2/3 bytes | 2 cycles* | ||||
| Absolute | AC | 3 bytes | 4 cycles* | ||||
| Direct Page | A4 | 2 bytes | 3 cycles* | ||||
| Absolute Indexed by X | BC | 3 bytes | 4 cycles* | ||||
| Direct Page Indexed by X | B4 | 2 bytes | 4 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| N | . | . | . | . | . | Z | . | |
LDY (Load Y) is a 65x instruction that loads a value into the Y index register. In immediate addressing only, LDY takes a total of 3 bytes when the index registers are 16 bits wide.
Syntax
LDY #const LDY addr LDY dp LDY addr, X LDY dp, X
Cycle Penalties
- In direct page addressing modes, LDY takes another extra cycle if the low byte of the direct page register is nonzero.
See Also
External Links
- Eyes & Lichty, page 464 on LDY
- Labiak, page 151 on LDY
- 7.1 on MCS6500 Manual, page 96 on LDY
- Carr, page 264 on LDY
- Leventhal, page 3-74 on LDY
- snes9x implementation of LDY: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L817
- undisbeliever on LDY: https://undisbeliever.net/snesdev/65816-opcodes.html#ldy-load-index-register-y-from-memory
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#LDY