#include P18F4520.INC
 
ORG 0x00
 
RES_L EQU 0x30
RES_H EQU 0x31
NUM1_L EQU 0x10
NUM1_H EQU 0x11
NUM2_L EQU 0x20
NUM2_H EQU 0x21
 
; Load first 16-bit number into registers (NUM1)
MOVLW 0x25    ; Lower byte of NUM1
MOVWF NUM1_L
MOVLW 0x03    ; Higher byte of NUM1
MOVWF NUM1_H
 
; Load second 16-bit number into registers (NUM2)
MOVLW 0x10    ; Lower byte of NUM2
MOVWF NUM2_L
MOVLW 0x02    ; Higher byte of NUM2
MOVWF NUM2_H
 
; Perform subtraction (LOW BYTE)
MOVF NUM1_L, W  ; Move NUM1_L into W register
SUBWF NUM2_L, W  ; W = NUM1_L - NUM2_L
MOVWF RES_L      ; Store result in RES_L
 
BTFSS STATUS, C  ; Check if borrow occurred
DECF NUM1_H, F   ; If borrow, decrement high byte
 
; Perform subtraction (HIGH BYTE)
MOVF NUM1_H, W
SUBWF NUM2_H, W
MOVWF RES_H
 
END
 

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