DEC MKA11 and/or M8261/M8163

Johnny Billquist bqt at
Sat Feb 14 13:24:43 CST 2015

On 2015-02-14 19:14, Paul Birkel wrote:
> 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.

The MKA11 is really not much different from an MK11, and you can use an 
MKA11 in a normal 11/70 system as well as far as I understand. 
Essentially, the MKA11 is just a multiported MK11 box. And the 
multiporting is achieved through this extra module, that fits (as far as 
I can remember) in the standard MK11 box.

All the other modules in the MKA11 are the same as in the MK11.

> 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)?

I don't think so. There is not out-of-band signalling. But you do have a 
control panel for the memory box, on which you can control the box. I 
would suspect this would be for that.
(I think there are some extra controls for an MKA11 compared to the 
standard panel of an MK11, which is for (I think) setting the memory 
on-/offline for individual CPUs, and possibly something more. It should 
be in the documentation I put in a link to.


> 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.

Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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