LDY: Difference between revisions

Revision as of 04:50, 20 November 2023


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.

External Links

Eyes & Lichty page on LDY: https://archive.org/details/0893037893ProgrammingThe65816/page/n489
Labiak page on LDY: https://archive.org/details/Programming_the_65816/page/n161
MCS6500 Manual page on LDY: https://archive.org/details/mos_microcomputers_programming_manual/page/n114
Carr page on LDY: https://archive.org/details/6502UsersManual/page/n277
Leventhal page 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

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-'''LDY''' (Load Y) is a 65x instruction that loads the [[Y index register]].  In [[direct page addressing]] modes, LDY takes another extra cycle if the low byte of the [[direct page register]] is nonzero.
+'''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 ===