Re: Carry propagation, +, T=0 ???
> > I will be very grateful to anyone pointing to me this part of the
> > documentation on MuP21 which explains this behavior. While waiting,
> > I will not be sparing NOPs.
Penio Penev wrote:
> As usual, I remind, that intructions execute in parallel, that is, if you
> put a nop, the carry propagates behind the scenes. The instruction itself
> _latches_ the result of the respective unit in TOS, that is you need nops
> _before_ the "instruction".
Thank you, this is indeed what happens - one should allow time
_before_ executing +, not after. Just consider + as a latch.
Let me quote again my manual from Offette enterprises, explaining +:
"As the adder is implemented with ripple carry, the results of the
addition will not be available immediately. The sum and the carry
will be stabilized in the next word."
Actually, they will never stabilize, if you put the + at the wrong
place, as in:
com + nop nop
nop nop nop nop
nop nop nop nop ....................( I tried it :-)
Yours is a fine explanation (though, it seems to me, different from
the above quoted). I am sorry I never read it put this way before.
Thanks again:
-----------------------------------
Assen Kolov <kolov@geocities.com>
