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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 =====
==== 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]] page 464, on LDY: https://archive.org/details/0893037893ProgrammingThe65816/page/n490
* [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/n490 page 464] on LDY
* [[Labiak]] page 151 on LDY: https://archive.org/details/Programming_the_65816/page/n161
* [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n161 page 151] on LDY
* [[MCS6500 Manual]] page 96 on LDY: https://archive.org/details/mos_microcomputers_programming_manual/page/n114
* 7.1 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n114 page 96] on LDY
* [[Carr]] page 264 on LDY: https://archive.org/details/6502UsersManual/page/n277
* [[Carr]], [https://archive.org/details/6502UsersManual/page/n277 page 264] on LDY
* [[Leventhal]] page 3-74 on LDY: https://archive.org/details/6502-assembly-language-programming/page/n123
* [[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

See Also

External Links