Mystery IC: Allen Bradley 314B102

Mike Ross tmfdmike at
Tue Dec 15 07:32:31 CST 2015

Solder side pic sent to your email! Thanks!
On Dec 16, 2015 2:22 AM, "Brent Hilpert" <hilpert at> wrote:

> 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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