LDY: Difference between revisions

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.

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

@@ Line 1: / Line 1: @@
-'''LDY''' (Load Y) is a 65x instruction that loads the [[Y index register]].
+{| class="wikitable" style="float:right;clear:right;width:40%"
-{| class="wikitable" style="float:right;clear:right;width:30%"
 !colspan="8"|Basic Info
 |+
@@ Line 9: / Line 7: @@
 |'''Speed'''
 |+
-|immediate
+|[[Immediate]]
 |A0
 |2 bytes
-|2 cycles
+|2 cycles*
 |+
-|absolute
+|[[Absolute]]
 |AC
 |3 bytes
-|4 cycles
+|4 cycles*
 |+
-|direct page
+|[[Direct Page Addressing|Direct Page]]
 |A4
 |2 bytes
-|3 cycles
+|3 cycles*
 |+
 |absolute indexed X
 |BC
 |3 bytes
-|4 cycles
+|4 cycles*
 |+
 |direct page indexed X
 |B4
 |2 bytes
-|4 cycles
+|4 cycles*
 |}
 {| class="wikitable" style="float:right;clear:right;width:30%"
-!colspan="9"|Flags Clobbered
+!colspan="9"|Flags Affected
 |+
-|N
+|[[Negative Flag|N]]
-|V
+|[[Overflow Flag|V]]
-|M
+|[[M Flag|M]]
-|X
+|[[X Flag|X]]
-|D
+|[[Decimal Flag|D]]
-|I
+|[[I Flag|I]]
-|Z
+|[[Zero Flag|Z]]
-|C
+|[[Carry Flag|C]]
 |+
 |
+|.
 |.
 |.
@@ Line 53: / Line 52: @@
 |.
 |
-|.
 |.
 |}
+'''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 ===
+* [[STY]]
 * [[LDA]]
 * [[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:Group Three Instructions]]
+[[Category:Inherited from 6502]]
+[[Category:Load/Store Instructions]]