Hand clocking CPUs
pete at dunnington.plus.com
Wed Jul 21 17:20:00 CDT 2010
On 21/07/2010 22:22, Eric Smith wrote:
> JP Hindin wrote:
> > Has anyone -tried- hand-clocking a Z80?
> Won't work on an original NMOS Z80 CPU, they were definitely dynamic.
> You could get away with somewhat slower than the minimum spec (about
> 246.3 kHz for a 4MHz NMOS Z80), but not at finger speed.
> Some of the later CMOS Z80 cores are static, some are not. In
> particular, the original Z180 was CMOS but dynamic. It may be the case
> that all CMOS Z80 CPUs (vs. Z180 and other derivatives) are static, I'm
> not sure. Check the data sheet for the specific part number you're using.
Hmm.. I've definitely done it, and on quite old parts on occasion. I
thought they were NMOS but they may have been CMOS, I suppose. And I
recall being told in the late 70s or possibly around 1980/81 that Z80s
were static -- that would be about the time I started poking at the
hardware in that sort of detail.
> If you hand-clock a static CPU, remember to debounce your button or
> switch. Switch bounce can have glitches faster than the minimum clock
> pulse width spec; I've seen them on an oscilliscope many times. Even
> if you don't get fast glitches, you'll still get multiple pulses when
> only one is desired.
That is definitely true.
Pete Peter Turnbull
University of York
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