Mystery IC: Allen Bradley 314B102

[Mike Ross]

On Tue, Dec 15, 2015 at 4:59 AM, tony duell <ard at p850ug1.demon.co.uk> wrote:
> Some more random thoughts....
>>
>> Of the above 10 pins, 11, 13, 22 & 23 are high at power-up (printer
>> NOT connected to any interface). The only pin with known function is
>> 19, which is 'paper out'; if I toggle the paper out switch I can see
>> it going high and low.
>
> Well, 19 could be a general printer-ready pin in that if the paper runs
> out it would say the printer is not ready for another character but
> it might well also be put to the not-ready state when the printer
> was printing the current character. Seen that before.

Maybe, but Selectrics aren't exactly fast devices; there's a whole lot
of potential 'no, wait, I'm not ready!' conditions. Would they all be
ORed onto one pin?


> Also, having now looked at the photos (sorry I was rushed before) I
> am pretty sure that Allen Bradley package is a pull-up resistor
> array. Half the pins seem to go to the +5V trace. The others go
> to signals

Confirmed off-list; it's a resistor network; 14 pins, seven resistors.

> Remember that a pulled-up logic input will test as a high level. So some
> or all of the 'high' pins might be inputs.

True and possible. But even if they're ALL inputs, only seven of them?

> I notice the 3 chips with the Pn lables. I think I can make out a Harris
> logo on one of them. I would guess these are programmed PROMs
> to convert between ASCII (I hope) and the solenoid codes for the
> Selectric.

That was my conclusion too. The old Western I/O ads I've seen
definitely refer to it as having an 'ASCII' or 'parallel' interface.
Assuming they only ever made the two models; I suppose it *could* be
some variant of RS232, with very non-standard pinouts - but the ads
are specific; they made a smart terminal with 6800 CPU & serial
interface, and a dumb printer with an 'ASCII parallel' interface. And
that's all I have to go on, beyond prodding the hardware.

> The next thing of interest to me is the pair of 7475 latches at the bottom
> of the board. 4 bits each. Maybe hold the 8 bit input character. I would
> trace where the D's and Q's of those go first.
>
> Perhaps you load the character a nybble at a time???

That would be well weird. Still trying to work out what exactly it was
intended to hook up to; a standard parallel port with a special cable,
using only four of the data lines, and a driver, to drive it
nybble-wise? Maybe I could use business records to try to track down
the former owner of 'Western I/O' and just ASK him, if he's still
alive, but that would be cheating :-)

I've gone over the connector again and we have ten signal pins plus a
ground plane... that's *just* enough for 8 data bits, a strobe, a
ready/wait line... but that Allen Bradley pull-up pack is only 14
leads, 7 lines... I'd expect to see 8 data lines all going to the same
place if it was anything resembling standard Centronics but with a
weird pinout. So I'm scratching my head still over just exactly what
it was supposed to hook up to.

> This board does not look that complicated and all the ICs have known
> numbers on them (mostly TTL logic). If it were mine I'd trace out the schematic.

That's true and possible. I'm in two minds on this thing:

- intention was to rip all this out and convert it to a full I/O
serial terminal, using an Arduino-based setup that Lawrence Wilkinson
has already built and tested:
https://www.flickr.com/photos/ljw/sets/72157632841492802/with/9201494189/
- all the keyboard contacts are already in there, Western I/O just cut
the IBM wires off when they ripped the IBM guts out and converted it
printer-only. I'd like to figure out the interface that's presently in
it, just to check out the mechanism, and for that 'ah ha!' moment :)
- but I don't want to spend any significant time on it if I'm just
going to rip it all out.

- but, although the Western I/O conversion 'butchered' a perfectly
good IBM 2970, it IS a rare representative of that era, when all kinds
of Selectric conversions were commonplace. So perhaps, as a nod to
that era, it should be left as-is, as a preserved example? What say
people? I've seen posts on old lists where people have referred to
buying these back in the day - converted Selectrics I mean - and
seeing 'mountains' of them in warehouses. They were once common. Where
have they all gone? Is mine the *only* survivor from those mountains
of 3rd-party backstreet conversions? Does anyone else have any?

I've just spent a few hundred bucks with one of the few mechanical
Selectric gurus left standing - a local guy here in NZ who did an
amazing job, several broken and seized bits fixed, the mechanism is
now like new and works perfectly in typewriter mode - so it's going to
end up working, one way or another!

Mike

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