--- Tony Duell <ard_at_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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Received on Wed Jun 19 2002 - 12:29:52 BST