28 Jul
2010
28 Jul
'10
2:42 p.m.
Tony Duell wrote:
You guys are going to force me to learn something about DEC gear yet.
:-) Not that I'd mind at all, aside from the fact that I already have
way too many interests. After considerable Googling I think I did learn
that SPC is the acronym for Small Peripheral Controller. Everyone has
to start somewhere, right? Then I re-read the email above and
discovered that you said that in the first paragraph! Arrrgggh. Well,
at least now I might remember that bit of information for a while.
This reminds me of a little saying I saw about a year ago and found
rather humorous. "If you want to be a guru in some area, the first
thing to do is memorize all the holy acronyms." I think there's a fair
amount of truth in that...
Later,
Charlie C.
On 7/27/10,
Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Actually, the original SPCs were 3 boards. A dual-height board containing
the specific device control/interface circuity that went in connectors C
and D of the SPC slot, an M105 address selector module in connector E and a
M782 (or M7820, M7821) interrupt logic module in connector F. That's why
there are connections betweeen the various connectos on the SPC slot.
I hae a DR11-A that's like that, and I think I have a KL11 (current loop
only console port) done that way too. And possibly some others.
Even when everything went on one quad-height SPC card, some devices still
consisted of 3 independant circuits on that card, connected via the
backplane connecotrs only, In other words there would be an address
selector circuit on the quad card conencted to connector E only. It would
output the approrpiate eanble signals on fingers of connector E, they
would then be routed to connector C/D via the backplane and thus to the
device logic. My PC11 is built that way.
I also have some 3rd party dual height cards that combine the functions
of the address sekector and interrupt logic and which go in connectors
E?F, along with a dual-height SPC card in C/D
-tony
Goin back ot the very early Unibus devices, there
were 3 cards -- the
device controlelr itself, an M105 address selector (which had jumpers to
set the device address) and an M782/M7820/M7821 Interrupt card which had
the jumpers to set the vector.
Good point. I had forgotten about those - all of
my comments apply to
SPCs (Small Peripheral Controllers), not backplane-sized devices
(there were a few SPCs even in the earliest days, like the LP11 I
mentioned).