DEC bus transceivers

Guy Sotomayor Jr ggs at
Wed Oct 26 09:14:36 CDT 2016

> On Oct 26, 2016, at 7:02 AM, Philipp Hachtmann <hachti at> wrote:
> Hi,
> On 10/25/2016 10:49 PM, Guy Sotomayor Jr wrote:
>> Secondary chip marked (only reputable vendors).  I currently have ~2500 8641
>> and several 100’s of the other variants.  Assuming 100% good parts, I have
>> enough stock to build at least 100 unibus boards (total) of various types that I
>> have planned.
>> And to forestall any questions on the topic, no I will not be selling any of the
>> chips individually.  They are there to allow me to build/sell the various Unibus
>> boards.
> Very enlightening.
> You're hoarding interface ICs with commercial second thoughts while deeming any usable alternative as not working crap. Sounds quite coherent!

I’m saying I won’t use another alternative until that alternative has been proven to work in large scale systems.  I have enough troubles with getting my Unibus systems to work with BC11A cables (which have always been marginal even “back in the day”).  Too much of the discussions on Unibus interfacing has been “hey, I’ll use (fill in the blank) chips I have, it should work”.  I’ll shut up about it when someone does an actual engineered design.

> BTW Why isn't there a separate list "ccbusinterfacechip" where those recurring 8881 discussions can be separated from the more interesting stuff?
> I just can't imagine that it should be a real problem to build working Unibus equipment without the old chips.

Because AFAIK, no one has done the actual engineering to come up with reliable replacements.  As I said, until that’s done I’ll stick with the old chips.

BTW, with modern designs (i.e. 3.3v I/Os) using the old interface chips is a pain.  First they’re 5v I/Os and 2nd they don’t do tri-state.  So you need a 2nd set of interface chips that are 5v tolerant and convert the I/Os (at least the ones you care about to tri-state.  I spend more board area and parts count on interfacing to the Unibus than actually implementing what I want.  For example, the MEM11A board has 3 active parts that are actually doing the work, all of the rest of the board and parts (over a dozen) are for interfacing to the unibus.

TTFN - Guy

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