[A83] Re: tst + tstio instructions
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[A83] Re: tst + tstio instructions
Do you have a specific address of where to get the docs?
>The statements about the P/M flag are mostly correct -- however not all
>instructions affect the P/M flag. Refer to the Zilog docs to see which do
>and which don't. Carry isn't always affected either. For example, INC r and
>DEC r don't affect the carry, even though there was a carry during the
>operation. Again, the Zilog docs list how all instructions affect the
flags.
>
>-----Original Message-----
>From: assembly-83-bounce@lists.ticalc.org
>[mailto:assembly-83-bounce@lists.ticalc.org]On Behalf Of Tijl Coosemans
>Sent: Tuesday, July 03, 2001 2:15 PM
>To: assembly-83@lists.ticalc.org
>Subject: [A83] Re: tst + tstio instructions
>
>
>
>The P/M flag has the same value as bit 7 of A. If it's set (negative
result)
>then the P/M flag is set, and you test that with M. If it isn't set
>(positive result) then the P/M flag isn't set (how obvious :-) and you test
>that with P.
>
>The carry you can see as the 9th bit of A. When A overflows (larger than
>$FF) then the carry is set. When the result is below 0 then the carry is
set
>either. Remember your first math classes. Then you had things like this
(but
>now in binary)
>
>ca 7 6 5 4 3 2 1 0
> 0 1 1 1 1 1 1 1 1
>+ 0 0 0 0 0 0 0 1
>------------------
> 1 0 0 0 0 0 0 0 0
>
>ca 7 6 5 4 3 2 1 0
> 0 0 0 0 0 0 0 0 0
>- 0 0 0 0 0 0 0 1
>------------------
> 1 1 1 1 1 1 1 1 1
>
>You see, the carry is set when a bit has been 'carried' over.
>
>In rotations and shifts, the carry has the same value as the bit that was
>shifted away, carried away.
>
>Tijl Coosemans
>
>
>
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