[vcf-midatlantic] Dec Ka670 bus?

Dave McGuire mcguire at neurotica.com
Sat Sep 7 15:51:58 EDT 2019

On 9/7/19 3:42 PM, W2HX via vcf-midatlantic wrote:
> I have been reading about the evolution of these vax processors starting at the KA630, KA650 etc. I just came across the KA670 which seems to have a new bus connector. Instead of the typical ABCD card edge connectors there is a 270 pin connector like a din or vme looking thing.
> Reading about it, apparently it still carries the Q22 bus, but also now has a memory bus (pmi? Gbus?) And a dssi bus.

  All Qbus VAX processors except for th KD32 (MicroVAX-I) have a PMI
bus.  The KD32 is the only Qbus VAX processor whose memory is directly
on the Qbus.

  The KA630 (MicroVAX-II) and KA650/655 (MicroVAX-III family) have PMI
buses using IDC connectors and ribbon cables bridging across the top of
the processor and memory boards.  The KA670 just moved it to the bottom
of the board to clean things up in the chassis.

> Very interesting! Anyone know if this type of backplane using these connectors has a name? Typically a bus is often synonymous with the physical connectors used, but in this case it is not. Not that it had to be but commonly it is.

  I don't recall the name for it, if it had one.  Everyone just viewed
it as a "bundle of buses", a convenient single-connector way to get the
PMI, Qbus, and power into the CPU board.  That connector itself wasn't
really regarded so much as a single bus as a collection of separate
buses that happened to share a connector.


Dave McGuire, AK4HZ
New Kensington, PA

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