HP 12653A line printer interface

J. David Bryan jdbryan at acm.org
Tue Jul 11 13:11:32 CDT 2017


On Monday, July 10, 2017 at 22:24, CuriousMarc wrote:

> I thought I did, but what I have is the HP 12845B Line Printer interface
> card, for which I could find the documentation.

Thanks for checking.  Yes, that does seem to be the more common card.  As 
far as I know, the 12653A was used only for the HP 2767 (a rebranded Data 
Products 2310), whereas the 12845B was used for a number of other HP 

> Reading some more, it is meant for the 2607/261x series of printers,
> which apparently use a narrower 7 bit interface (the 12566 is a 16 bit
> interface card).

Which is all a bit odd, as the 2767 also uses 7 bits for data.  Unlike the 
other printers that use differential interfaces, the 2767 uses single-ended 
TTL-level (more or less) drivers and receivers, which may explain the use 
of the microcircuit-based interface.

The 2767 signal drivers are adjustable for a 3- to 8-volt output level, so 
perhaps the 12635A "modification" was to clip the inputs to avoid damaging 
the standard microcircuit receivers (7400 TTL with an absolute maximum 
input spec of 5.5 V).  In the absence of a manual, I was hoping that a 
photograph would reveal the modification.

> But maybe you can inspire yourself from it.

The existing 2767/12653 simulation was reverse-engineered from the 
diagnostic and OS drivers.  Although it works, I was hoping for something 
more authoritative so that the code could serve as a reference for the 
now-extinct hardware.

                                      -- Dave

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