LDX: Difference between revisions

Latest revision as of 21:57, 9 January 2024


Basic Info
Addressing Mode	Opcode	Length	Speed
Immediate	A2	2 bytes*	2 cycles*
Absolute	AE	3 bytes	4 cycles*
Direct Page	A6	2 bytes	3 cycles*
absolute indexed Y	BE	3 bytes	4 cycles*
direct page indexed Y	B6	2 bytes	4 cycles*


Flags Affected
N	V	M	X	D	I	Z	C
	.	.	.	.	.		.

LDX (Load X) is a 65x instruction that loads the X index register. In immediate addressing only, LDX is a total of 3 bytes long when the index registers are 16 bits wide.

Cycle Penalties

In direct page addressing modes, LDX takes another extra cycle if the low byte of the direct page register is nonzero.

External Links

Eyes & Lichty page 463, on LDX: https://archive.org/details/0893037893ProgrammingThe65816/page/n489
Labiak page 150 on LDX: https://archive.org/details/Programming_the_65816/page/n160
MCS6500 Manual page 96 on LDX: https://archive.org/details/mos_microcomputers_programming_manual/page/n114
https://archive.org/details/mos_microcomputers_programming_manual/page/n219, lbid.
Carr page 264 on LDX: https://archive.org/details/6502UsersManual/page/n277
Leventhal page 3-72 on LDX: https://archive.org/details/6502-assembly-language-programming/page/n121
snes9x implementation of LDX: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L772
undisbeliever on LDX: https://undisbeliever.net/snesdev/65816-opcodes.html#ldx-load-index-register-x-from-memory

@@ Line 1: / Line 1: @@
-'''LDX''' (Load X) is a 65x instruction that loads the [[X 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]]
 |A2
-|2 bytes
+|2 bytes*
-|2 cycles
+|2 cycles*
 |+
-|absolute
+|[[Absolute]]
 |AE
 |3 bytes
-|4 cycles
+|4 cycles*
 |+
-|direct page
+|[[Direct Page Addressing|Direct Page]]
 |A6
 |2 bytes
-|3 cycles
+|3 cycles*
 |+
 |absolute indexed Y
 |BE
 |3 bytes
-|4 cycles
+|4 cycles*
 |+
 |direct page indexed Y
 |B6
 |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: @@
 |.
 |
-|.
 |.
 |}
+'''LDX''' (Load X) is a 65x instruction that loads the [[X index register]].  In [[immediate addressing]] only, LDX is a total of 3 bytes long when the index registers are 16 bits wide.
+===== Cycle Penalties =====
+* In [[direct page addressing]] modes, LDX takes another extra cycle if the low byte of the [[direct page register]] is nonzero.
+*
+*
 === See Also ===
+* [[STX]]
 * [[LDA]]
 * [[LDY]]
 === External Links ===
-* [[Eyes & Lichty]] page on LDX: https://archive.org/details/0893037893ProgrammingThe65816/page/n489
+* [[Eyes & Lichty]] page 463, on LDX: https://archive.org/details/0893037893ProgrammingThe65816/page/n489
-* [[Labiak]] page on LDX: https://archive.org/details/Programming_the_65816/page/n160
+* [[Labiak]] page 150 on LDX: https://archive.org/details/Programming_the_65816/page/n160
-* [[MCS6500 Manual]] page on LDX: https://archive.org/details/mos_microcomputers_programming_manual/page/n114
+* [[MCS6500 Manual]] page 96 on LDX: https://archive.org/details/mos_microcomputers_programming_manual/page/n114
-* [[Carr]] page on LDX: https://archive.org/details/6502UsersManual/page/n277
+* https://archive.org/details/mos_microcomputers_programming_manual/page/n219, lbid.
-* [[Leventhal]] page on LDX: https://archive.org/details/6502-assembly-language-programming/page/n121
+* [[Carr]] page 264 on LDX: https://archive.org/details/6502UsersManual/page/n277
+* [[Leventhal]] page 3-72 on LDX: https://archive.org/details/6502-assembly-language-programming/page/n121
+* snes9x implementation of LDX: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L772
+* undisbeliever on LDX: https://undisbeliever.net/snesdev/65816-opcodes.html#ldx-load-index-register-x-from-memory
 [[Category:ASM]]
 [[Category:Group Two Instructions]]
 [[Category:Inherited from 6502]]
+[[Category:Load/Store Instructions]]