Detailed reference for the CLRF instruction in PIC18 ISA.
Clear the contents of a file register f. The register is set to 0 and no value is written back to WREG. The a operand selects the address space: a = 0 for the access bank, a = 1 for a banked area.
; a=0 → Clear register in Access bank
CLRF 0x20, 0 ; 0x20 = 0x00; a=0 → Clear register in Access bank
CLRF 0x20, 0 ; 0x20 = 0x00; a=1 → Clear register in Banked address
CLRF 0x20, 1 ; 0x20 = 0x00 (banked); a=1 → Clear register in Banked address
CLRF 0x20, 1 ; 0x20 = 0x00 (banked)