Univac panel and mystery TTL chips

[Tony Duell]

> >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.

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.

> 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. 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