Analyzer was Re: KIM-1 repair advice wanted
Peter C. Wallace
pcw at mesanet.com
Fri Oct 7 11:56:50 CDT 2005
On Fri, 7 Oct 2005, Dwight K. Elvey wrote:
>> From: "Hans Franke" <Hans.Franke at siemens.com>
>> First thing would be
>> to connect a logic analyzer to see if the CPU is still running
>> a programm in ROM or not.
> What is it with logic analyzers. Why not just an
> oscilloscope. In most cases, one can be farther along
> with an 'oscope in finding what is wrong by the
> time one can get an analyzer connected and setup.
> I've only had one time that I ever needed an analyzer
> and even that time, it didn't work well because
> of the complexity of the problem ( design not failure ).
> I'll admit that I've often thought of making one
> of those address compare circuits to trigger the 'scope
> but by the time I'd get serious, I'd found the problem.
> Am I alone here or does everyone else think that an
> analyzer is the ultimate tool?
I have one but rarely use it:
1. With modern circuits it is nearly impossible to connect.
2. Usually by spending a little more time thinking and doing simple
measurements (address and data toggling, clocks running, reset doing the
right thing) I can avoid using the logic analyser at all.
3. for repairing older circuits, often the problem will
maniifest itself as a marginal level, the LA may miss this completely
or give hard to interpret results.
4. Just having a simple oscillator to toggle the reset line lets me trace the
first few CPU instructions with nothing more than a scope (and a piece of
5. I do have some pre-configured ROM socket --> logic analyser adapters so I
can trace startup code when bring up a new board.
Basically I only use it as a last resort when nothing else works...
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