Plessy core memory

Noel Chiappa jnc at
Mon Jan 10 10:59:32 CST 2022

    > From: Chris Zach

    > I'm guessing that the DD11-F is significantly different from the DD11-B?

I assume theat "DD11-F" is a typo; there is, AFAIK, no DD11-F, and a Web
search revealeddidn't turn anything up. (There are DD11-CF and -CK
backplanes, as well as -DF and -DK, but the -CF and -CK differ only in power
harness length.)

    > the 11/24 used +12 on the +15 lines. No idea what was wrong with DEC


I'm guessing it used the parts that the IC vendors could provide.

    > Don't know what would happen if you plugged a RL11 or other hex height
    > card into one of those slots, probably blow everything up.

Not sure. Per:

These are _some_ of the MUD/EUB pin clashes:

  AN1 - A21 - Parity P1
  AP1 - A20 - Parity P0
  BE1 - A19 - Internal SSYN
  BE2 - A18 - Parity Detect

I don't think those would harm anything. Not sure about power pins - and have
no incentive to research it, as I have no need/interest in trying it.

  > I know I ran it with two of these Plessy cards and a RX01 controller but
  > now that I look at it that would be impossible as both were hex cards

Maybe Plessey designed them to go in a DD11-B? I know I've seen other
third-party cards that would go in oddball slots.

    > and both could never fit in a 4 slot backplane with enough space for a
    > quad spc

Why not? The two hexes in slots 2&3, the quad in 1 or 4.

    > a DA11-F Unibus window

Wow; never heard of those. I'll have to do a CHWiki page for them. Luckily,
the maint manual is online. There's also a DA11-B.

    > what would happen if I enabled the KT24 Unibus memory map.....

All that does is allow DMA devices on the -11/24's UNIBUS access to the
entire main memory:

So if you hooked up an -11/10 to an -11/24 with a DA11-F, then with the UNIBUS
Map on, the -11/10's CPU and/or DMA devices would have access to the entire
EUB memory via the 24's UNIBUS Map, is all.

    > This is so much fun!

That _is_ why we collect old computers! ;-)


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