Further 11/40 unibus questions...

Johnny Billquist bqt at softjar.se
Tue Jun 2 03:52:25 CDT 2009

Paul Anderson <useddec at gmail.com> wrote:

> I always used a M930 in the 11/40 and older machines, and the M9300 in the
> 11/34 and newer machines. I have no way to check on the differences
> now. now.  Also, there may be a trick using MOS in an 11/40.

I can't remember that there should be any functional difference between 
a M930 and a M9300. The later is just an improved design.

As for the original posters problems. When you get a stuck machine when 
the terminator is in, but a somewhat more functional machine when the 
bus terminator is out, you have a problem on the bus. Most likely a bus 
grant or NPR grant. A third possibility is a problem in the CPU with the 
logic related to these signals.

I'd go over the bus grants once more. Check that they *really* are the 
right way, since it's so easy to put them in the wrong way, and there is 
basically no visible clue to which way they should go.
Look at some other card to get help. They will also have connections on 
the same places the BG cards have, except they will likely run them up 
to the priority plug. If you have some Unibus memory, they are nice, 
since they have the BG lines wired straight through, just like the BG cards.

I would have started by removing *all* cards from the Unibus (with the 
exception of some memory), and make sure all bus grants and NPRs were 
in, the terminator was in place and that all power supplies were 
delivering the right voltage. Also check that all cards in the CPU box 
are in place, and are firmly seated.


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

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