3 Sep
2009
3 Sep
'09
1:27 p.m.
-----Oorspronkelijk bericht-----
Van: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] Namens Tony Duell
Verzonden: donderdag 3 september 2009 21:41
Aan: cctalk at classiccmp.org
Onderwerp: Re: Omrom programmable terminal
I have the signature analyser and the logic comparator.
The signature analyser is usefull if you have a HP equipment with the
according serv. Manual under test.
Fault finding goes rather quick then, the logic comparator is only usefull
with clock frequenties below aprox. 10Mhz above that the cable impedance is
to big.
Using a Fluke 9100A boardtester is much more usefull, because you can test
in cuircit ram, drivers and processor.
I keep the HP stuff for collecting purpose ;-)
And it's nicely build...
-Rik
But the thing that caught my eye was the HP 548A
"logic clip"--a
device built into a DIP test clip with an LED for each pin. It
featured self-seeking logic and would display the state of all pins
for RTL, TTL, DTL and CMOS logic families. It sounds very
cool--and I
have never seen one in the flesh.
I have (both the HP one and clones), but I don't own one. To
be honest, it _looks_ cool, but it's fairly useless. The ones
I used had no pulse-stretching circuitry, the LEDs just
displayed the state of each pin (on for '1', off for '0' and
on-but-dim for toggling -- the brightness depended on the
mark/space ratio). It was OK on slow circuity, but that's
easy to debug anyhow. On anything with a reasonable clock
frequency, it didn't tell you much.
HP made a couple of other devices that I don't own and could
never see the point of. One was the 'signature analyser'
which will tell you if a logic signal differes from the
correct version (well, provided you have a 'correct version'
to also test) but won't tell you _how_ it differs. So
actually finding the fault doesn't seem to be any easier.
The other is the 'logic comparator' which effectively lets
you connect a known-good example of a simple (SSI, MSI) TTL
chip to the one under test.
The inputs get the same signals, the outputs of the 2 chips
are compared.
Any differences are shown on LEDs. It seems to me to be a
very slow way of findign a fault by just testing each chip,
rather than actually looking for the symptoms and working out
what's wrong.
-tony