MM11-U/UP core memory backplanes

william degnan billdegnan at
Sun Feb 28 13:34:14 CST 2016

On Sun, Feb 28, 2016 at 12:37 PM, Noel Chiappa <jnc at>

>     > From: Bill Degnan
>     > Very useful, thanks.
> Eh, de nada - glad to help contibute to the knowledge base.
>     > I will try this.
> With MM11-U gear, or MM11-L?
> I ask because, like I said, I still don't have 100% clarity on the MM11-L
> situation. I am pretty sure there are old MF11-L backplanes that can't be
> upgraded to parity this way (i.e. removing the jumper), and may not be
> upgradable to parity at all (i.e. it might take etch cuts that are
> 'impossible', if they are on the bottom side of the PCB).
> There's that jumper that should be there on non-parity units, but does not
> seem to be there on some older backplanes (so you can't remove it to make
> the
> backplane parity-capable); arguing that it's probably hard-wired in the
> etch
> on those older backplanes? And there seem to be a couple of pins that need
> to
> be bussed acros, for the MM11-L units to 'talk' to the parity controller.
> And
> if the parity jumper isn't there, logically those bussing etches might not
> be
> there either.  So I have a little work ahead of me with an ohm-meter...
> Speaking of the jumper, and bussed signals: the parity board input pin that
> that jumper is connected to (when the parity board is not there) must be
> bussed to all three group locations in the MF11-L backplane, as a wired-OR
> of
> their proto-SSYN outputs. If it were daisy-chained among the three groups,
> you've have to put the board sets in in a specific order, no? (Otherwise a
> gap
> would lose the signal from the group(s) on the far side of the gap.)  And
> there's nothing like that in the manual. Something else to check out on the
> prints and/or with a meter..
> Anyway, please report back on your experiences, so if there's any useful
> info you pick up, we can learn from it.
>         Noel

My thought is that with my PDP 11/05 with S chassis / BA11-K.  I am
thinking I could apply this knowledge to my situation, even if it's not the
exact match.  I have the same memory and controller cards H217C and H217D
(parity / non parity) to play with in the same chassis, if I can locate
what jumper to change.


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