NES ca65 Cheat Sheet

gistfile1.md

This cheat sheet is only for the ca65 assembler, and probably not compatible with others

adc - Add to the accumulator

lda #1 ; A = 1
adc #1 ; A = 2
ldx #5 ; X = 5
stx $01 ; memory address $01 = 5
adc $01 ; A = 7

sbc - Subtract from the accumulator

8-bit subtraction:

sec ; set the carry flag
lda #5
sbc #1 ; subtract one from the A register, A = 4

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dec - Decrement a value in a memory address by one

lda #5
sta $01 ; Memory address $01 holds the value 5
dec $01 ; Memory address $01 holds the value 4

asl - Left-bit shift the accumulator

lda #1 ; A = 1 (00000001)
asl    ; A = 2 (00000010)
asl    ; A = 4 (00000100)

The leftmost bit of the accumulator is set to the carry flag

lda #%10000000 ; A = 128 (10000000), carry flag = 0
asl            ; A =   0 (00000000), carry flag = 1

pha - Push accumulator onto the stack

lda #1 ; A = 1
pha    ; A = 1, $01FF = 1

pla - Pull (pop) value from stack into the accumulator

lda #1 ; A = 1

txs - Set the value of the stack pointer

Typically you'll just do this once to setup a descending stack

txs #$ff

ora - Logical inclusive OR performed on the accumulator

lda #%10101010
ora #%11110000
; A = 11111010