General Question about UNIBUS backplanes

Mark Darvill mark.darvill at
Sun May 22 12:22:49 CDT 2016

The core memory/CPU backplane is a special case and doesn’t need grant cards.

If you have linked up to the expansion Unibus then you need to check you have the NPG jumper in row C, Pins A1 and B1 in each slot. If these do not have wire wrap then you will either need to wire wrap them or insert a G727 into the backplane slot. Without these the units will hang on attempting to use a card that requires DMA access.

Hope this helps.


> On 22 May 2016, at 18:10, tony duell <ard at> wrote:
>> Are you saying remove all of the GC cards, just leave the slots blank?
> Yes, from the slots that are designed to take the core memory or its
> controllers (I assume, given you have special backplanes, there are 
> boards with the core planes on, and more boards with the XY drivers
> or the sense/inhibit logic on). 
> Do you have a diagram of where the core boards should go. If so, are
> there slots in the backplane left over. What are those 'extra' 
> slots for?
> -tony

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