Rudy Wieser
;----------------------------
; 16-bit Subtraction-with-Borrow
; SourceH:SourceL - Number to be subtracted
; Carry - NOT( Borrow to be subtracted )
; DestH:DestL - Number to be subtracted FROM
;Out DestH:DestL - Result
; Carry - NOT( Borrow result)
movf SourceL,W
subwf DestL
movf SourceH,W
btfss STATUS,C
incfsz SourceH,W
subwf DestH ;dest = dest - source, WITH VALID CARRY
;(although the Z flag is not valid).
;----------------------------