Detailed reference for the ANDLW instruction in PIC18 ISA.
Perform a bitwise AND between the 8‑bit value in WREG and an 8‑bit literal k. The result overwrites WREG.
The literal can be specified in decimal, hexadecimal (0x) or octal (0) format. This instruction has no destination (d) or bank (a) bits; it always writes back to WREG.
; AND literal with WREG
ANDLW 0x0F ; W = W & 0x0F; AND literal with WREG
ANDLW 0x0F ; W = W & 0x0F; Load W with 0xF0 then AND it with 0x0F
MOVLW 0xF0
ANDLW 0x0F ; W = 0xF0 & 0x0F = 0x00; Load W with 0xF0 then AND it with 0x0F
MOVLW 0xF0
ANDLW 0x0F ; W = 0xF0 & 0x0F = 0x00