Hand clocking CPUs

John Robertson pinball at telus.net
Wed Jul 21 14:51:21 CDT 2010


Dave McGuire wrote:
> On 7/21/10 1:17 PM, JP Hindin wrote:
>   
>> I was reading something the other day about being able to hand-clock a
>> Z80, that it was so stable (due to not using dynamic registers,
>> apparently) that with the appropriate debounce circuit you could literally
>> manually step it through instructions.
>>
>> Is this as rare as it sounds?
>>
>> Has anyone -tried- hand-clocking a Z80?
>>     
>
>   Umm yes, it's called single-stepping, and it's very common.  The first
> Z80 system I had that had support for that built-in was my IMSAI 8080.
> I used single-stepping to debug my BIOS modifications in the mid-1980s.
>
>   And yes my IMSAI "8080" is actually a Z80 system...It has a CCS 2810
> CPU board which is compatible with the IMSAI front panel circuitry. :)
>
>   A single-stepping circuit for a Z80 is pretty simple.
>
>             -Dave
>
>   
The only problem I could see is if the RAM memory is dynamic and one 
made the mistake of single stepping the board master clock rather than 
the Z-80 CPU clock. Static RAM wouldn't care...

John :-#)#



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