6 Apr
2013
6 Apr
'13
11:19 p.m.
David Riley <fraveydank at gmail.com> wrote:
Definitly an option I would
want to keep. Too bad there aren't any 9-slot mixed layout backplanes, but as DEC
compatible backplane connectors seem to surface sometimes, so I see at least the
possibility of constructing one, should the need materialize.
Well, you *could* work around it that way. I guess
Kapton would
probably be a good bet. You're very unlikely to be using early LSI-11
boards unless you're a true masochist (...)
Uhm, people have already been calling me that (in a classiccmp context!), so...
Be aware that if you're using the system as
18-bit, you'll
need to make sure that your peripheral cards are jumpered to 18-bit if
necessary (boards that use DMA often need to know).
The 22-bit conversion is also easy to undo, assuming you're handy with
a soldering iron (...) For me, undoing that would be about as easy as looking up
which pins to cover and then covering them with tape (...)
Hmm, I'm just "planning for eventualities"; Basically I want to build a
system that runs in a 22-bit configuration, but I'm trying to make sure I can still
stick in 18-bit CPUs (or other cards) for a quick test after I do the conversion.
(or custom
logic, if you had that).
Sounds interesting, could you elaborate?
(...) There were probably quite a few other board sets that used
the CD lines for inter-board communication (...)
(very nice description of CD interconnect principles) I wouldn't swear to the fact that there
weren't 11/23s sold as 18-bit
systems; my fuzzy memory says that 11/23 might have been 18-bit while
11/23+ would have been 22-bit. Other people doubtless know better
than me; my other recollection is that the "plus" distinction has to
do with the KDF11-B board (which has the boot ROM and SLUs).
Christian Gauger-Cosgrove <captainkirk359 at gmail.com> wrote:
I don't know anything about how DEC sold their
machines, but I do believe
they did sell the 11/23 as an 18-bit system (even though the KDF11A is very
much capable of 22-bit) (...)
Hmm, let's see...
(supposedly extracted
from Micronote #5 dated 23-Apr-84):
RESTRICTED COMPATIBILITY OPTIONS:
PROCESSORS:
KDF11-A M8186 LSI-11/23 CPU
Prior to etch rev. C, 18-bit addressing only,
and use of BC1, BD1, BE1, BF1 for purposes
other than BDAL18-21.
...so the systems using these earlier revisions, while being 11/23s by definition, would
have to be based on 18-bit backplanes due to the nonstandard signals. This is also
consistent with Christian's statement:
as I remember there is a "PDP-11/23" version
of
the BA11-N box (with H9273-A, the BA11-N always has the H9273-A)
I think I actually might be having the remains of such an early system, as it says
"11/23" on the outside but holds an (18-bit) H9273 backplane inside.
Alas I haven't readily found a DEC source on what actually is the PLUS in an 11/23+.
Thank you so far,
Arno