LDX: Difference between revisions

Latest revision as of 06:38, 22 August 2024


Basic Info
Addressing Mode	Opcode	Length	Speed
Immediate	A2	2/3 bytes	2 cycles*
Absolute	AE	3 bytes	4 cycles*
Direct Page	A6	2 bytes	3 cycles*
Absolute Indexed by Y	BE	3 bytes	4 cycles*
Direct Page Indexed by Y	B6	2 bytes	4 cycles*


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

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

Syntax

LDX #const
LDX addr
LDX dp
LDX addr, Y
LDX dp, Y

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
Labiak, page 150 on LDX
7.0 on MCS6500 Manual, page 96 on LDX
B-18, lbid.
Carr, page 264 on LDX
Leventhal, page 3-72 on LDX
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
Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#LDX

@@ 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 10: / Line 7: @@
 |'''Speed'''
 |+
-|immediate
+|[[Immediate]]
 |A2
-|2 bytes
+|2/3 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
+|[[Absolute Indexed by Y]]
 |BE
 |3 bytes
-|4 cycles
+|4 cycles*
 |+
-|direct page indexed Y
+|[[Direct Page Indexed by 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
+|+
+|[[Negative Flag|N]]
+|[[Overflow Flag|V]]
+|[[M Flag|M]]
+|[[X Flag|X]]
+|[[Decimal Flag|D]]
+|[[I Flag|I]]
+|[[Zero Flag|Z]]
+|[[Carry Flag|C]]
 |+
 |N
-|V
-|M
-|X
-|D
-|I
-|Z
-|C
-|+
-|
 |.
 |.
 |.
 |.
-|
 |.
+|Z
 |.
 |}
+'''LDX''' (Load X) is a 65x instruction that loads a value into the [[X index register]].  In [[immediate addressing]] only, LDX is a total of 3 bytes long when the index registers are 16 bits wide.
+==== Syntax ====
+<pre>
+LDX #const
+LDX addr
+LDX dp
+LDX addr, Y
+LDX dp, Y
+</pre>
+==== 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]]
+* [[TAX]]
+* [[TYX]]
+* [[TSX]]
+=== External Links ===
+* [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/463 page 463] on LDX
+* [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n160 page 150] on LDX
+* 7.0 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n114 page 96] on LDX
+* [https://archive.org/details/mos_microcomputers_programming_manual/page/n219 B-18], lbid.
+* [[Carr]], [https://archive.org/details/6502UsersManual/page/n277 page 264] on LDX
+* [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n121 page 3-72] on LDX
+* 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
+* Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#LDX
 [[Category:ASM]]
+[[Category:Group Two Instructions]]
+[[Category:Inherited from 6502]]
+[[Category:Load/Store Instructions]]