Writing a 3-byte binary subtraction subroutine - Microcontroller Programming-EEWORLD

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An easy programming question for microcontrollers! Urgent, write a 3-byte binary subtraction subroutine.

When using the main program to call multiple groups of data for debugging, two situations need to be considered: the situation with and without borrow.

Input: Minuend: 52H, 51H, 50H, 50H is the lowest bit;
Subtrahend: 42H, 41H, 40H, 40H is the lowest bit;
Output: Difference: external data storage 2003H~2000H (2000H is the lowest bit).

There are three bytes involved in the subtraction, and the addresses are continuous, so just loop three times.

    MOV R0, #50H ;Address of minuend
    MOV R1, #40H ;Address of subtrahend
    MOV DPTR, #2000H ;Address of difference
    CLR C
    MOV R2, #3 ;Loop 3 times
S_LOOP:
    MOV A, @R0 ;Get
    SUBB A, @R1 ;Subtract
    MOVX @DPTR, A ;Store
    INC R0
    INC R1
    INC DPTR
    DJNZ R2, S_LOOP
    CLR A
    SUBB A, #0 ;Get borrow
    MOVX @DPTR, A ;Store
    RET

Reference address：Writing a 3-byte binary subtraction subroutine - Microcontroller Programming

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