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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 the [[Y index register]]. In [[immediate addressing]] only, LDY takes a total of 3 bytes when the index registers are 16 bits wide. | ||
==== Syntax ==== | |||
<pre> | |||
LDY #const | |||
LDY addr | |||
LDY dp | |||
LDY addr, X | |||
LDY dp, X | |||
</pre> | |||
===== Cycle Penalties ===== | ===== Cycle Penalties ===== | ||
Revision as of 22:41, 6 July 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 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 | |
| . | . | . | . | . | . | |||
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.
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: 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