[Coco] Assembler Question???
tvefoo at yahoo.com
Fri Sep 4 06:48:11 EDT 2009
>There is actually no sub tractor but,
According to the book: Microprocessor- Microcomputer Technology by
Frederick F. Driscoll. It says, "In all uPs, subtraction is done by
2's complement arithmetic. If the result is negative, the answer is
in 2's complement form. For example, if the problem is 4 - 7 = -3, the
answer, -3, in 2's complement form is 11111101 (binary). Microprocessors
have instructions that can check the logic state of bit 7, the most
significant bit of the answer. If bit 7 is a logic 0, the answer is
positive; if bit 7 is a logic 1, the answer is negative. Hence, a
positive or negative answer can easily be determined."
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