LDX

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. The size of the index registers determines whether this is an 8 or 16 bit operation. If 16-bit and not using immediate addressing, the low-order byte is located at the effective address and the high-order byte at the effective address plus one.

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 all addressing modes, LDX takes an extra cycle when the index registers are 16 bits wide
• In direct page addressing modes, LDX takes another extra cycle if the low byte of the direct page register is nonzero.
• In Absolute Indexed, Y Addressing, LDX takes an another extra cycle if adding the index crosses a page boundary

See Also

• STX
• LDA
• LDY
• TAX
• TYX
• TSX

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