Mystery IC: Allen Bradley 314B102

Ethan Dicks ethan.dicks at
Mon Dec 14 20:56:39 CST 2015

On Mon, Dec 14, 2015 at 9:15 PM, Fred Cisin <cisin at> wrote:
> On Tue, 15 Dec 2015, Mike Ross wrote:
>> I thought Centronics dated back to early 1970s - not always in the
>> standard 'modern' form, but in general principles with same signaling
>> and strobing of data.
> I got in late.  My first encounter with Centronics was TRS80 (1979?)
> At that time, Centronics did not yet have a monopoly on parallel
> "protocols", although the company had certainly been around for a while.

My first experience was in the mid-1980s.  Someone gave me an ancient
tank of a Centronics-brand printer - 132 columns and 2 print heads!
One head got the left side of the paper, the other head got the right
side.  Unlike the later "Centronics Interface", this one had an
internal edge connector for input - 40 or 44 pins (I used a standard
44-pin protoboard but I can't remember if I had to cut it down or not)
 I interfaced it to the user port on my Commodore 64 and wrote my own
handler to trap device #4 and squirt out the data through the user

> Once they got the TRS80 market, and then the IBM PC market, any other
> designs faded away fast.

Yep.  About the only exceptions I can think of are the Amiga 1000
(proprietary but similar parallel port pinout on a DB25M) and DEC
minicomputers which leaned towards the Dataproducts-type interfaces
that required a gate or two (and probably a cable pin swabber) to talk
to "modern" Centronics printers - one example was the DC37 on the back
of a VAX-11/730... you had to add somewhere between 1-3 inverters to
make that talk "Centronics" but once you did, you could just tell the
VMS line printer process to squirt chars out the parallel interface
and it would "just work".


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