6 Oct
2005
6 Oct
'05
12:14 p.m.
At 07:46 PM 10/6/05 +0100, you wrote:
Be warned that this sort of test depends critically on the particular
logic family, and the type of ohmmeter in use.
As you hace the chip on a circuit board, you can easily find pins that
are tied to +5V or ground (you _must_ be able to find those 2 rails on
the board, if nothing else by starting from a chip you know the
number and pinout of). OK, there may be pins other than the Vcc and Gnd
pins that are connected to those points on the unknown chip (e.g. unused
inputs), but I think you should be able to indentify the actual power and
ground pins fairly easily.
They also got a good number of the crosses from instrument service
manuals. Unlike the calculator manuals, the instrument manuals usually gave
the HP PN, manufacturer code and manufacturer's PN. I supplied a lot of the
instrument part number listings to Sphere also some of the numbers from the
dual marked parts.
Then you might be abloe to identify some pins as
definite inputs (driven
from totem-pole outputs on known ICs), others as definite outputs (only
go to known inputs).
If all else fails you may have to desoler the IC, power it up on a
breadboard, find outputs with a logic probe, try the inputs, and so on.
I used to have an article out of one of the electronics magazines that
told how to identify various pins on ICs using an ohm meter. Input pins,
output pins and power and ground pins all have different characteristics. Unfortunatly I lost the article. Does anyone have
any info on how to go
about doing this?
How about starting with a known IC of the family you're interested in and
recording the results for your meter between various combinations of the
pins?
But all in all I like Tony's Suggestion of looking for the parts with
dual markings and make a cross reference list. When you get done, post it
on the net to benefit everyone. Spere has a good start on HP and Tektronix
cross reference on their website.
I know for a fact that some of the IC's on that HP list were indetified
by finding dual-marked ones on HP boards. And others were indentified by
finding inputs and outputs and indentifying the functions. I know this,
because I did it :-)
There was a good HP equivalent list published _by HP_ in Bench Briefs at
one point.
Bench Briefs published a series of issues with cross references. I don't
remember if each one carried a different range of PNs or if they broke them
up by equipmnet useage or what but I know the cross reference was spread
over a good number of issues. I had a fair number of BBs but never had the
whole cross reference.
Joe
It was half a dozen pages, 3 columns, fairly small font. I
haev it, but I know it wouldn't stand scanning or
copying, and I don't
feel like typing it all in.
-tony