[Coco] Assembler Question???
jdaggett at gate.net
jdaggett at gate.net
Thu Sep 3 14:36:34 EDT 2009
On 2 Sep 2009 at 20:33, Robert Gault wrote:
> jdaggett at gate.net wrote:
> >
> > Steve
> >
> > 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.
> >
> > james
> >
>
> 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.
>
Robert
Thanks. What that tells me is that negative numbers are represented as their 2's
compliment.
james
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