Unibus Termination KnowledgeQuest

Don North ak6dn at mindspring.com
Thu Oct 12 15:51:15 CDT 2006

Jay West wrote:
> Don wrote....
>> The issue is there are two different aspects of the UNIBUS that are 
>> being terminated:
> Aha. Now that makes sense! Thank you :)
> What that means to me then is that in the /34 the 9302 should only be 
> plugged in to a the AB unibus out slot and NOT in a MUD slot, 
> otherwise, you get a funny smell I bet :)

Correct ... the M9302 terminator is a UNIBUS slot device.

The difference between the AB UNIBUS vs the AB MUD (Modified UNIBUS) is 
that AB UNIBUS has grounds and BG1_H~BG4_H,NPG_H on pins that AB MUD 
uses for +20V core, -15VBB, +15VBB and some internal SPC slot parity 

> So what about the 9312 in the /34 then. I assume it can only  (no 
> matter HOW it's jumpered) be put in a MUD (AB) slot, never in an AB 
> unibus slot (Unibus in or Unibus Out). ??
You wouldn't want to put in in the UNIBUS out. You still need to 
terminate both ends of the bus, you want an M9302 somewhere to process 
SACK timeout, and you can have at most one M9312 in the system. So the 
only config that meets all these is M9302 in 9AB, and M9312 in 3AB.

> Then, this of course brings me back to my dearly beloved (sarcasm) 
> /45. In that machine, the cpu doesn't terminate anything from what I 
> understand, hence the 930 at the front in slot 1AB. I assume in the 
> /45 then, you CAN put the (appropriately jumpered) 9312 in the last 
> slot (unibus out), and that you don't put another 930 in that slot and 
> put the 9312 in a prior AB slot. Is that all correct?
This I will have to defer to someone else. The M9312 doc's indicate 
there are jumper wire settings (W1-W12) to allow it be in either a MUD 
(standard position) or for 'other UNIBUS CPUS with M9312 in place of 
M930'. I would assume this to mean that one of the M930s (which I assume 
is the 'old' M9302 without the SACK timeout logic) can be replaced by a 
correctly configured M9312, but you still need the other M930 at the 
other end of the bus.

Or, just speculating here, what about an M9312 at the front of the bus, 
and an M9302 at the end of the bus (kinda like the 11/34 config)? This 
would require some research to make sure it doesn't smoke anything. 
Caveat emptor to be sure.

> Thanks so much!
> Jay

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