21 Jul
2010
21 Jul
'10
5:43 p.m.
On 7/21/10, JP Hindin <jplist2008 at kiwigeek.com> wrote:
Hey;
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?
I suppose that depends on your definition of rare. It's an uncommon
feature in modern processors, but probably not uncommon in the 8-bit
world.
A friend of mine, the older brother of the guy who taught me machine
code on an Elf long, long ago, was debugging his own Elf (RCA CDP1802)
and being a high school student in the 1970s, did not own much in the
way of "fancy" test gear. He certainly didn't own an oscilloscope.
So when he was having problems figuring out what was wrong with his
Elf, he built a debounced push button and connected it in place of the
1MHz crystal. The timing diagrams in the RCA manuals are very clear
and very complete. My friend stepped through the
8-clock-pulses-per-machine-cycle and watched his machine cycle through
its various states (conveniently brought out on a pair of lines) and
was able to debug his machine with an analog meter (used as a logic
probe, essentially).
Has anyone -tried- hand-clocking a Z80?
Me? No.
-ethan