PDP-12 Restoration at the RICM
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
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
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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