[Coco] Assembler Question???
robert.gault at worldnet.att.net
Wed Sep 2 20:33:37 EDT 2009
jdaggett at gate.net wrote:
> It is not the SUB command that I was querrying. What the main inquiry was if the
> assembler converted a binary number and stored it as a 2's compliment or not.
> I used it because if my assumption were true, then that would be the most likely
> command to do it with. There is no way that I know of in logic gates to make a subtractor
> other than by taking the subtrahend and converting it to its 2's complement and then
> add. You can do the same with 10's complementer and then add decimal to do decimal
> subtraction and so forth and so forth.
There was a poor example in my first message but regards the assembler
vs the ALU ....
ADDA #-1 gives $8B $FF
SUBA #1 gives $80 $01
and the other pair
ADDA #1 gives $8B $01
SUBA #-1 gives $80 $FF
In short, the assembler uses twos complimentary notation but does not
convert subtractions into additions.
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