Making computer IC signals directly visible -Reply

[RONDO JEFFERY <RJEFFERY@weber.edu>]

William Beaty posed the following experimental situation:
> ...
> Wire up a single-chip microprocessor which has a UV-erase window.
> Program it, remove the window, set up the clock speed to be something
> around 3Hz, attach a battery, then view it under the SEM.  The
> thousands of conductors on the surface of the operating computer will
> flash with black/white voltage signals.
> ...

Bill,
One problem I see with this is that most microprocessors have a minimum
clocking frequency that they can operate at due to the requirement for
memory to be refreshed at a minimum rate.  Of the early microprocessors
(8080, 6502, Z80, etc.) only the Z80 could be clocked as slowly as you
propose.  Zilog used static registers which could be clocked manually, if
you wanted to.  All the others used dynamic registers which had a minimum
refresh rate--otherwise you lose your charge and hence the logic status. As
microprocessor chips have become denser in terms of transistor count,
almost all have become MOSFETs of some sort (NMOS or CMOS, usually),
I'm sure none use static registers anymore.  Hence, none could be clocked
as slow as a few Hz.

But it does sound like a "cool" experiment--if it would work.

Rondo Jeffery
Physics Dept.
Weber State University
Ogden, UT 84408-2508
RJeffery@weber.edu