3 Jun
2005
3 Jun
'05
6:37 p.m.
Tony wrote:
Unibus and Qbus use the same double-sided 36 pin (18
pin per side) 0.125"
pitch connectors. Q bus boards are normally dual or quad, Unibus are
normally quad or hrx.
To be overly pedantic:
Unibus boards are normally dual. The only real Unibus boards you're likely
to find are the terminators and bus jumpers. If someone tries to tell you
that a quad or hex board is a Unibus board, they're almost certainly
mistaken, and it is probably really an SPC or MUD/SPC board. Normally
the only Unibus slots in a PDP-11 backplane are the A-B positions of the
first and last slots, though there are exceptions to that in various
places such as the PDP-11/45 and RH11 backplanes.
SPC ("Small Peripheral Controller") boards are quad or hex.
MUD/SPC ("Modified Unibus Device") boards are hex.
SPC and MUD/SPC boards are commonly but incorrectly called Unibus boards,
but they will not work correctly in a Unibus slot (and technically they
won't even fit).
Extended Unibus slots are found only in the PDP-11/24 and PDP-11/44
processor backplanes and are only used for MS11-M (M8722) and
MS11-P (M8743) memory boards or third-party equivalents.
In some backplanes, one or both Unibus slots (in the first or last
position) are colinear with an SPC slot. Do NOT try to use a hex
SPC or SPC/MUD board in that slot.
Because PDP-11 systems have quite a variety of different slot assignments,
and even conflicts regarding voltages (15V for core, 12V for semiconductor
memory), people maintaining PDP-11 systems actually need to understand
this stuff.
Eric