PIC18 cheatsheet
ADDWFADDWFCANDWFCLRFCOMFCPFSEQCPFSGTCPFSLTDECFDECFSZDCFSNZINCFINCFSZINFSNZIORWFMOVFMOVFFMOVWFMULWFNEGFRLCFRLNCFRRCFRRNCFSETFSUBFWBSUBWFSUBWFBSWAPFTSTFSZXORWF
BCFBSFBTFSCBTFSSBTG
BCBNBNCBNNBNOVBNZBOVBRABZCALLCLRWDTDAWGOTONOPPOPPUSHRCALLRESETRETFIERETLWRETURNSLEEP
ADDLWANDLWIORLWLFSRMOVLBMOVLWMULLWRETLWSUBLWXORLW
TBLRD*TBLRD*+TBLRD*-TBLRD+*TBLWT*TBLWT*+TBLWT*-TBLWT+*

SUBFWB

Detailed reference for the SUBFWB instruction in PIC18 ISA.

Description

Subtract the contents of file register f and the borrow flag from WREG.

  • d = 0 → result stored in WREG.
  • d = 1 → result stored back into register f.
  • a = 0 → Access bank addressing.
  • a = 1 → Banked addressing.
  • The borrow flag is the status bit C; if C = 0, a borrow of 1 is subtracted, otherwise 0.
  • Status flags updated: Z (zero), DC (borrow from bit 3), V (overflow), and C (set if no borrow, cleared if borrow).

Examples

; d=0, a=0  → result in WREG, Access bank
SUBFWB 0x20, 0, 0   ; W = W - 0x20 - borrow
; d=0, a=1  → result in WREG, Banked address
SUBFWB 0x20, 0, 1   ; W = W - 0x20 - borrow (banked)
; d=1, a=0  → result back to file register, Access bank
SUBFWB 0x20, 1, 0   ; 0x20 = W - 0x20 - borrow
; d=1, a=1  → result back to file register, Banked address
SUBFWB 0x20, 1, 1   ; 0x20 = W - 0x20 - borrow (banked)
; Load literal into WREG then subtract with borrow, result in WREG (Access bank)
MOVLW 0x07
SUBFWB 0x05, 0, 0   ; W = 0x07 - 0x05 - borrow