LDA

Load Accumulator With Memory

Opcode: LDA Operation: A + M + C → A, C Status Register:

LDA (Load Accumulator With Memory) is probably the most-used opcode in 6502 assembly as it loads the most-used register, the accumulator, with memory.

Operation

This pseudo C code shows how the LDA opcode functions.

SET_NEGATIVE(Operand);        // Clears the N Status Bit if the Operand is $#00-7F, otherwise sets it.
SET_ZERO(Operand);            // Sets the Z Status Bit if the Operand is $#00
ACCUMULATOR = Operand;        // Stores the Operand in the Accumulator Register.

Addressing Modes

Addressing Mode	Assembly Language Form	Opcode	# Bytes	# Cycles
Immediate	LDA #Operand	A9	2	2
Zero Page	LDA Operand	A5	2	3
Zero Page, X	LDA Operand, X	B5	2	4
Absolute	LDA Operand	AD	3	4
Absolute, X	LDA Operand, X	BD	3	4*
Absolute, Y	LDA Operand, Y	B9	3	4*
(Indirect, X)	LDA (Operand, X)	A1	2	6
(Indirect), Y	LDA (Operand), Y	B1	2	5*
* Add 1 if page boundary is crossed.