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Substract 16bits nos with 8085
- Thread starter papier
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You need to use an instruction common in most uP's called "subtract with borrow" or "subtract with carry." It's usually 'SBB' or 'SBC'. On the Intel 8086, you can do 16-bit math using 8-bit registers via:
mov al,byte ptr subtrahend
sub al,byte ptr minuend
mov byte ptr result,al
mov al,byte ptr subtrahend[1]
sbb al,byte ptr minuend[1]
mov byte ptr result[1],al
presumably the 8085 code isn't too far off... "Information has a tendency to be free. Which means someone will always tell you something you don't want to know."
mov al,byte ptr subtrahend
sub al,byte ptr minuend
mov byte ptr result,al
mov al,byte ptr subtrahend[1]
sbb al,byte ptr minuend[1]
mov byte ptr result[1],al
presumably the 8085 code isn't too far off... "Information has a tendency to be free. Which means someone will always tell you something you don't want to know."
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