11/24 board settings (Re: Next project: 11/24. Does it need memory?)

Jay Jaeger cube1 at charter.net
Fri Nov 13 17:16:21 CST 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.)
> 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]".

CPU E124 S6 is indeed ON, so if the TM is right, only the high addresses
go to the UNIBUS.  Skeptical of that, unless by UNIBUS they mean "UNIBUS
other than memory".

UNIBUS MAP no "TP" wires, so the lowest UNMAPPED address would be
740 000 if the TM is accurate.  The only wire in is  W13 (ROM enabled)
near as I could tell.

Labeled M7891-BB.  Presumably 128KB (64KW).

The M7891 (MS11-L) is addressed at 0 as near as I can tell -  S2 (E61)
switches are all ON, and it appears to be set for the default 4K I/O
Page from 124K to 128K.

My manual EK-11024-TM-001 (not -003).

>     > 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.

Yes, it is a BA11-A (10.5" tall).  Do you know offhand where that power
adapter is?  I fear you'd be asking me to disassemble the backside of
the power supply, or, worse, take the power supply out, which I am not
inclined to make happen.  ;)

There is a schematic of what I think is the board you are referring to
on bitsavers at


PDF page 161 of 200 (5413815)

> 	Noel

More information about the cctalk mailing list