Mystery IC: Allen Bradley 314B102

Brent Hilpert hilpert at
Mon Dec 14 23:06:00 CST 2015

On 2015-Dec-14, at 2:02 PM, Mike Ross wrote:
> - 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:
> - 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!

Well, I vote for doing a little more work to get it working as is.
If it's all there, it 'should' work as intended and really doesn't look to be very complex.
Chances look good it will be adaptable to a centronics port.

Pin 9-11 & 21-24 connect to the pull-up resistors and head in the the direction of the 7475 DFFs - that's likely the 7 data bits.
Traces from the DFFs look like they then head to the proms which are likely 3 * 256*4.
That leaves 13,17,19 for some combination of control signals such as print-strobe-in, ready-out, fault-out.

I notice there is an MC14490 hex contact debouncer there. You say this is not a keyboard-send conversion, so I'd guess those debouncers may be picking up mechanical contacts that indicate end-of-operation, to produce a ready signal.

If reverse engineering really isn't your shtick, send along reasonable-resolution photos of both sides of the board and I'll work on a schematic.
Could do it with the photos you provided earlier except the solder-side photo isn't complete.

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