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

Jay Jaeger cube1 at
Thu Oct 22 10:02:30 CDT 2020

On 10/21/2020 11:36 AM, Noel Chiappa via cctalk wrote:
>     > 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.)

No idea how it is configured as it has always "just worked".  Factory as
a guess.  Will pull it and document it.

> 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.
> 	Noel

It's the BA11-A - 10.5" flavor.  I'll take photos you requested here and
document the board jumpers and switches over the next week or so, for my
own use, if nothing else.


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