UK PDP11 wanted

Glen Slick glen.slick at
Tue Apr 14 16:44:25 CDT 2015

On Tue, Apr 14, 2015 at 2:16 PM, Noel Chiappa <jnc at> wrote:
> Actually, the PMI signals are all (I'm pretty sure, but have not checked) just
> like most other QBUS signals - 'broadcast' bi-directionally down a
> transmission line. The 'PMI memory before the CPU' thing in 11/83's is simply
> an artifact of the way 'standard' Q/CD backplanes are wired on the CD side
> (used for PMI) - see that second post for details.
MSV11-J MOS Memory User's Guide
Page 4-7, Table 4-3 Backplane Pine Utilization
3. All PMI signals except PBYT have the connectors on side 1 etched to
the respective signal on side 2 of the module.

So the backplane doesn't directly bus the PMI signals across all Q/CD
slots in a BA23 / BA123 chassis, but when PMI memory boards are
installed above and adjacent to the M8190 CPU the PMI signals are
bused through one PMI memory board to the one above and adjacent to
it, if any.

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