PDP-12 Restoration at the RICM

Vincent Slyngstad v.slyngstad at frontier.com
Tue May 26 13:10:45 CDT 2015

From: Mike Ross: Tuesday, May 26, 2015 5:48 AM
> Do tell more about this mythical and very useful sounding board tester?

Warren's tester is similar in basic capability to the one that Henk and 
I did some time ago, with some additional circuitry that's useful for 
"load testing" -- telling the difference between an M6xx and an M1xx 
card, etc.

Basically, ours had some I/O registers that you could set to control 
I/O direction, and some latching transceivers to drive test vectors 
to the module and read back results from the module.  This was 
done on a platform driven through a serial port talking to a 6802

Warren's design, as mentioned by Michael, uses a set of SPI ports, 
talking to 23S17 chips, which allow you to configure I/O direction, 
set the test vector, and receive the result.

In addition, he's set up some LEDs and various loads and pull-ups, 
which can be configured as needed to more accurately load the 

This all works quite well for "slow" testing of combinatorial logic.
It's more cumbersome to come up with test vectors for sequential 
logic, though it can (usually) be done.

Level converters can be added for B/R/S series modules, though the
design of those while preserving the ability to set the I/O direction 
is a bit of a pain (in terms of both cost and component count).

I think for more general testing (Gxxx?), it may be necessary to have 
proper "pin drivers", somewhat like those used in PROM programmers.

For more dynamic testing, some me kind of local processing is 
probably needed to judge the dynamic properties of a response, 
and it may not be good enough to have to serialize and un-serialize 
the data.

A shortage of gumption and relevant skills has kept me from being 
helpful for a while now...

> I'm looking at my racks and racks of logic, mostly M-series - 12, 16,
> 18, & 36 bit - and contemplating the debuggering with some dread...

Mine are all 12 bit, but me too.


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