Mystery IC: Allen Bradley 314B102

[Mike Ross]

On Wed, Dec 16, 2015 at 4:35 AM, tony duell <ard at p850ug1.demon.co.uk> wrote:
>>
>> I guessed that might be the case... any suggestions for what were
>> common pinouts and signals used? I can analyze 'backwards', testing
>
> There were just about as many parallel interface versions as devices
> that used them back then..... Nothing 'common' really...
>
> The idea of 7 or 8 data lines, a strobe, and a ready signal was
> certainly arround back then, but the timing, polarity (active high
> or low) and timing were not standardised. A couple of examples
> that I can see without getting up are the Facit 4070 paper
> tape punch and the HP9866A thermal printer. Those were
> both around in the early-mid 1970s and are rather different
> parallel interface.
>
> OK, what I would do to get some idea is focus on those 7475 chips. Get
> the pinout. The most obvious use for them on this board is as the
> character input latch. IIRC each is really 2 2-bit latches, so 2 enable/clock
> pins on each chip. So :
>
> 1) Are the 4 clock pins linked together (if so, it loads a character at a time [1]),
> or are they in pairs or what
>
> 2) Where do the D inputs go? Are any of them linked together, or do 7 or
> 8 of them go to the interface connector? If the latter, then those are the data
> inputs.
>
> [1] Before anyone suggests you could use them as a sort-of shift register and load
> half a character into one, then copy it into the second one while loading the other half
> character, remember the 7475 is a transparent latch, not an edge-triggered flip-flop
> making this a very difficult thing to do.
>
> If you can identify the data lines on the connector you are getting there. See if you
> can trace the other pins to inputs or outputs.
>
> -tony

Tony, good advice but probably more work than I'm inclined to put in.
As you said there were many interfaces with different standards -
different polarities and timing - and either way it's quite likely
this will never work with a standard modern parallel port without
building some converter, after first finding out what has to be
converted and designing it!

There are seven lines in parallel all going through that Allen Bradley
pullup network so I'm tentatively assuming it's accepting seven bit
parallel data so one character at a time - not nybbles or anything
else. That leaves three other lines which I'm assuming are some kind
of strobe; 'busy' or a functional equivalent; and the one we know is
'paper out'. That's enough for a working interface. Timing and levels
undetermined as you said.

I did have what I technically refer to as a 'poke' at it last night;
sent some text to the raw parallel device from a Linux box - and was
able - inconsistently - to get the Selectric mechanism to cycle
intermittently by rapidly inserting and removing jumpers in the
breakout box on the seven presumed data lines; essentially triggering
a kinda 'manual' strobe. So something is kinda sorta getting through
and I think I may leave it at that - unless I stumble across any doc.
I tried it with the presumed 'busy' and 'strobe' lines connected in
various ways that might make logical sense but could never get it to
'just work' and accept and print characters or continuously print a
stream of characters; it just cycled the mechanism intermittently on
manually making and breaking connections on the data lines as I said.
So I suspect the strobe/busy signaling is something different from
standard parallel. And of course I have no idea of the bit order on
those data lines; I have a seven-way matrix of possible combos so
hitting the right one to actually print valid characters might be a
job of work!

If and when I do remove the Western I/O stuff and convert it to the
Arduino full serial terminal I'll photograph document and keep what I
remove - so it could be restored to 'as converted' condition in the
future if anyone wants to try it!

Mike

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