Mystery IC: Allen Bradley 314B102

[tony duell]

> 
> > 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?

Why not? It's all the host really needs to know -- can I send another
character or not.

[...]

> 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

Why 8 data bits? ASCII (which we are assuming this is) is a 7 bit code.
A number of older printers did indeed only have 7 parallel data lines.

> > 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:

I reckon it would take me a couple of hours at most.....

> - 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:

In some ways I agree with doing that (other than using a a million more 
components than you need...). On the other hand this board is part of the
history of the unit, so I would keep that if at all possible I think.

-tony