DEC MKA11 and/or M8261/M8163

Paul Birkel pbirkel at
Sat Feb 14 12:14:09 CST 2015

Thanks Eric.  That might explain how I came into possession of one M8162
module.  The 11/74 never entered my mind because encountering even a piece
of one of those is ... unlikely :->.  Using up unsold inventory makes
sense; I guess that an MKA11 wouldn't function without a full complement of
modules, even if some serve no real purpose.

I've looked more closely at the pair of top-edge connectors (the ones like
the 20ma SLU connectors).  Each have 6-of-8 pins wired *thru* a 1K 1%
resistor to a separate pin on tab F.  So there are twelve lines running to
tab F, with resistors in series, and nothing else on those paths.

The rest of the module is a mix of S and LS SSI chips, and a couple of what
appear to be multi-tap delay lines, plus 5 diagnostic LEDs (unlabeled).

Would the KB11-CM have had special cabling to connect in this manner for
out-of-band signaling, and then why series resistors (rather than, e.g.,
pull-ups for an OC line driver)?

On Wed, Feb 11, 2015 at 2:55 PM, Eric Smith <spacewar at> wrote:

> On Sat, Feb 7, 2015 at 7:25 AM, Paul Birkel <pbirkel at> wrote:
> > I don't understand the role of the M8162 "Port MUX A module" and M8163
> > "Port MUX B module" that the field-guide claims to be part of the MK11.
> > They aren't part of the MK11 as far as any documentation that I've read
> > regarding it. [...]
> > Do these modules really belong to the MKA11, rather than the MK11?
> The MKA11 was the multiported version of the MK11, intended for
> multiprocessor (11/72 and 11/74) systems. it makes sense that it would
> have some "port mux" modules, though I've never seen any documentation
> on it.
> Reportedly some 11/70 systems were sold to AT&T with the KB11-CM CPU
> and MKA11, apparently just as a way to use up the hardware that was
> built for the cancelled 11/74.

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