--- Tony Duell <ard(a)p850ug1.demon.co.uk> wrote:
BTW, the 'example Unibus Interrupt' schematic
in the PDP11 Bus Handbook
that I have is _very_ close to the internal logic of the DC013 chip. The
giveaway is the fact that said example schematic has all external
connections numbered, and those turn out to be the pin numbers of the
DC013.
When Software Results made COMBOARDs, we chose to go with DEC's chips
for that reason - they were debugged and understood and worked. We
used the DC013s for Unibus designs, and the Qbus chipkit for Qbus
designs (VAXBI designs *mandated* the BIIC, so it wasn't optional).
I know we did our own DMA design so I have a pad of DC006 chips, but
we did use the DC010 and DC005 and DC004s (probably the DC003s, too).
I know we also used the 8641 where we didn't use a DEC chip. I _wish_
we'd used some of the older stuff (8881, 384, etc.) even though they
are deprecated, I would have had spares for OMNIBUS machines, etc.
The one disadvantage of DEC's chips was that they were expensive - ISTR
$125/set for Qbus chips at one point. OTOH, for a board that retailed
for $2,000 as a spare (no software license), it's a small percentage,
but it was still one of the most expensive line items after the board
itself.
I know other vendors used things like the 74LS240 for BDAL buffers
on the Qbus. Probably not spec, but it would work for most applications.
We've had this thread before - what reasonable substitutions are. I
was re-reading the Q22 IDE page mentioned earlier this week - he uses
8838 chips to buffer the dual 50-pin cables off of a Q22 extender. I
was thinking of rolling one of these for myself. The problem is, of
course, no VMS driver. Have to roll that, too. :-(
-ethan
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