PDP-11 memory question

From: Tom Leffingwell <tom_at_sba.miami.edu>
Date: Sat Jan 5 15:34:12 2002

On Sat, 5 Jan 2002, Pete Turnbull wrote:

> Two other things occur to me. The first is that memories like the MSV11-D
> (M8044) and MSV11-L (M8059) have jumpers to enable or disable memory that
> corresponds to the I/O page. This gets a little complicated... Most DEC
> memories decode the BBS7 signal to sense access to the I/O page and disable
> memory access accordingly. The MSV11-D has a jumper 1-2 to enable memory
> in the lower 2KW of the I/O page for systems that don't use the whole I/O
> space; jumper 2-3 (the factory setting) to disable memory in the whole top
> 4KW. The MSV11-L has a similar arangement, using jumpers 28-29 to enable
> the memory in the bottom half of the I/O page, and 27-28 to disable it.

        My old MSV11-D module was set 1-2 (enabled). The MSV11-L that I
replaced it with was jumpered 27-29 (disabled). I did find on the MSV11-L
that X was connected to U. I'm not sure what U is for, but seemed to be
grounded, so I removed it, which I assume set the address back to 0. At
that point it started working.

        How do I know whether or not I need to enable or disable I/O page
setting? I haven't tried to enable it on the MSV11-L, although it was
enabled on the MSV11-D before I removed it. What symptoms occur if its
set wrong?

> And that's the second thing. The MSV11-L doesn't use BBS7 for everything
> it decodes, so you have to set it according to whether it's in a 22-bit
> system or an 18-bit system. If there's a jumper from R-T, it's set for a
> 2MW system. Remove it for 128KW systems.

I did find out that I have the 22-bit KDF11-A, although I haven't checked
the backplane yet. If the backplane is 22-bit, should put the R-T jumper
in the M8059? Does it matter if I only have 128KW of memory?

Thanks,

Tom
Received on Sat Jan 05 2002 - 15:34:12 GMT