14 Apr
2015
14 Apr
'15
2:44 p.m.
On Tue, Apr 14, 2015 at 2:16 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu> 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.
http://www.bitsavers.org/pdf/dec/qbus/EK-MSV1J-UG_001_May85.pdf
MSV11-J MOS Memory User's Guide
Page 4-7, Table 4-3 Backplane Pine Utilization
NOTES:
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.