Hand clocking CPUs

Pete Turnbull 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
						Network Manager
						University of York



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