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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]]. | {| class="wikitable" style="float:right;clear:right;width:40%" | ||
!colspan="8"|Basic Info | |||
|+ | |||
|'''Addressing Mode''' | |||
|'''Opcode''' | |||
|'''Length''' | |||
|'''Speed''' | |||
|+ | |||
|[[Immediate]] | |||
|A0 | |||
|2 bytes | |||
|2 cycles* | |||
|+ | |||
|[[Absolute]] | |||
|AC | |||
|3 bytes | |||
|4 cycles* | |||
|+ | |||
|[[Direct Page Addressing|Direct Page]] | |||
|A4 | |||
|2 bytes | |||
|3 cycles* | |||
|+ | |||
|absolute indexed X | |||
|BC | |||
|3 bytes | |||
|4 cycles* | |||
|+ | |||
|direct page indexed X | |||
|B4 | |||
|2 bytes | |||
|4 cycles* | |||
|} | |||
{| class="wikitable" style="float:right;clear:right;width:30%" | |||
!colspan="9"|Flags Affected | |||
|+ | |||
|[[Negative Flag|N]] | |||
|[[Overflow Flag|V]] | |||
|[[M Flag|M]] | |||
|[[X Flag|X]] | |||
|[[Decimal Flag|D]] | |||
|[[I Flag|I]] | |||
|[[Zero Flag|Z]] | |||
|[[Carry Flag|C]] | |||
|+ | |||
| | |||
|. | |||
|. | |||
|. | |||
|. | |||
|. | |||
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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. | |||
===== 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 === | === See Also === | ||
* [[STY]] | |||
* [[LDA]] | * [[LDA]] | ||
* [[LDX]] | * [[LDX]] | ||
=== External Links === | |||
* [[Eyes & Lichty]] page 464, on LDY: https://archive.org/details/0893037893ProgrammingThe65816/page/n490 | |||
* [[Labiak]] page 151 on LDY: https://archive.org/details/Programming_the_65816/page/n161 | |||
* [[MCS6500 Manual]] page 96 on LDY: https://archive.org/details/mos_microcomputers_programming_manual/page/n114 | |||
* [[Carr]] page 264 on LDY: https://archive.org/details/6502UsersManual/page/n277 | |||
* [[Leventhal]] page 3-74 on LDY: https://archive.org/details/6502-assembly-language-programming/page/n123 | |||
* 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 | |||
[[Category:ASM]] | [[Category:ASM]] | ||
[[Category:Group Three Instructions]] | |||
[[Category:Inherited from 6502]] | |||
[[Category:Load/Store Instructions]] |
Latest revision as of 21:58, 9 January 2024
Basic Info | |||||||
---|---|---|---|---|---|---|---|
Addressing Mode | Opcode | Length | Speed | ||||
Immediate | A0 | 2 bytes | 2 cycles* | ||||
Absolute | AC | 3 bytes | 4 cycles* | ||||
Direct Page | A4 | 2 bytes | 3 cycles* | ||||
absolute indexed X | BC | 3 bytes | 4 cycles* | ||||
direct page indexed X | B4 | 2 bytes | 4 cycles* |
Flags Affected | ||||||||
---|---|---|---|---|---|---|---|---|
N | V | M | X | D | I | Z | C | |
. | . | . | . | . | . |
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.
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: https://archive.org/details/0893037893ProgrammingThe65816/page/n490
- Labiak page 151 on LDY: https://archive.org/details/Programming_the_65816/page/n161
- MCS6500 Manual page 96 on LDY: https://archive.org/details/mos_microcomputers_programming_manual/page/n114
- Carr page 264 on LDY: https://archive.org/details/6502UsersManual/page/n277
- Leventhal page 3-74 on LDY: https://archive.org/details/6502-assembly-language-programming/page/n123
- 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