Are Unibus and Qbus fingers mechanically/electrically compatible?

[oktology]

Particularly, can a Unibus double-height cable work as a Qbus cable?

 

[AK6DN]

DEC used the same edge card connector finger design of 18 connections, double sided, 36 connections per blade very early on.
Starting with the individual one blade and two blade flip chip modules, thru the two/four/six blade UNIBUS, QBUS, and OMNIBUS modules.
They are all mechanically compatible, and that is all. They are NOT universally electrically compatible. Power and ground connections do differ.
The answer to your particular question is a resounding NO. Don't even try it. There are power supply and ground connection incompatibilities.

 

[pbirkel@gmail.com]

They are NOT universally electrically compatible. Power and ground connections do differ.
The answer to your particular question is a resounding NO. Don't even try it. There are power supply and ground connection incompatibilities.

In particular it is not uncommon for bus extension modules to cross-connect multiple bus-specific power rail and/or ground pins at both ends of the cable. Not a good thing when when you want to preserve discrete signal integrity instead. If you have a "Unibus double-height cable" in hand then you can check for yourself whether all signals are uniquely preserved end-to-end. Note that the standard Qbus bus extension modules adhere to certain loading requirements (120 vs 220 vs 240 ohm) depending on length; see the combined M9404 with M9405-YA/YB variants and Qbus specifications for the details. The Qbus was more finicky in this regard than the Unibus with its support for quite lengthy extensions (vs. the minimal-length M920/M935 and folded-segment M9202) without specific additional loading. So don't expect that even if signal integrity is preserved that you can just add a 10 foot extension cable between two Qbus backplanes and everything will be automatically A-OK.