27 Oct
2013
27 Oct
'13
8:03 p.m.
On 27/10/2013 02:30, Jerome H. Fine wrote:
As for the PDP-11/03 you mention, it is my impression
that
BDAL18-21 must be wired - maybe with power on one or
more of those lines whereas with the dual PDP-11/23 CPU
(M8186 board), BDAL18-21 must be either empty (which
is a Q18/Q18 in that case) or wired ONLY to each other
(Q22/Q22). Specifically, a PDP-11/23 (M8186 board)
must not be inserted into a backplane (and power turned
on) wired for the PDP-11/03 (or LSI-11/03).
Not so. The 11/03 backplanes don't do anything dangerous with the lines
that would otherwise be BDAL18-21 (BC1,BD1,BE1,BF1). They're simply not
connected together. The 11/03 processors, both dual and quad versions,
put some odd signals there, and the earliest (Rev.A) KDF11-A dual cards
(M8186) also did (but not the same odd signals). It was very common,
for example, to replace an 11/03 CPU with a KDF11-A, particularly in
BA11-N boxes, and no other change was necessary. Even the 4x4 H9270
backplane in a BA11M is OK; DEC merely list it as "restricted
compatibility" because it is "18-bit addressing only" -- DEC even listed
a special version called H9270-Q that was 22-bit and fully compatible,
with the extra lines bussed.
I forget who asked that question, but my
understanding
differs. With the VT103 backplane which is a 4 slot
ABCD (QQ/QQ) serpentine, if a dual M8196 is in
1 AB, then 2 AB must also be used - either with a
useful dual board or a dual bus grant board. Can
someone else please verify this point as to which is
correct?
Yes, you are correct -- if you have a dual card in AB of the top slot in
any serpentine backplane, and you need to preserve the grant chain, then
you must have either a dual card or a grant card in CD of that slot. If
you don't care about the grant chain (and some systems don't) then it
doesn't matter. In this respect the top slot is no different to any other.
--
Pete Peter Turnbull
Network Manager
University of York