Next project: 11/24. Does it need memory?

Noel Chiappa jnc at
Wed Oct 21 11:36:48 CDT 2020

    > From: Jay Jaeger

    >> 2--M7134 KT24 Memory map

    > M7891 UNIBUS Memory (256K, I think, presumably addressed for 0).

If that's all the memory you have, the KT24 isn't really doing anything
(well, monitoring power; holding boot PROM's; etc). Is your MS11-L configured
to be EUB memory, then? If no KT24 is plugged in, the CPU detects that there
isn't one there, and permanently, statically maps the UNIBUS straight across
to the bottom 256KB of EUB space. (Presumably a low-cost option for the /24.)

Although the 'straight across' mapping only applies to UNIBUS->EUB cycles,
not EUB->UNIBUS cycles, such as those from the CPU; but the TM says [pg 2-31
in the 003 version] that if E124-S6 is OFF, "the lower 18 bits of every
address go to the UNIBUS", which implies that when OFF, UNIBUS memory appears
at 0 in the CPU's address space. So it should work as UNIBUS memory, with
E124-S6 OFF; it would be interesting to verify that. The TM also says (pg.
2-40) "systems with UNIBUS memory ... require changes to be made to the
mapping jumpers [on the KT24]".

    > Let me know if you want me to go thru the process of
    > ..
    > 2) Pull the boards and document

What kind of box is your -11/24 in, a BA11-A, or BA11-L?

If the latter, I'd be really grateful for some closeups of the interior, so I
can put mine back together, and do some of these experiments. (Yes, yes, I
know I should have taken pictures before I took it apart; I was just
starting, and was going by how we used to do things, back before there were
digital cameras.) I could probably work it out by staring hard, and thinking
harder, along with the prints, but photos would be a lot easier! :-)

If it's a BA11-A, I'm still trying to get an image of the special power
adapter used to turn the bus bar of the BA11-A into the 6/15 pin Mate-N-Lok
connectors used by the -11/24 backplane.


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