14 Oct
2012
14 Oct
'12
11:52 a.m.
On 10/14/2012 02:39 PM, David Riley wrote:
I don't think so. I've been thinking about this off-and-on for a few
years now. Yes, you'd need to spend some board space, but with more
modern high-integration components for the rest of the functionality (on
the other side of the bus interface) one really doesn't need to have all
THAT much board real estate left over. I think it could be done with a
couple of transistors per line, and using even relatively large SOT-23
packages, one would likely burn less than 1/3 of the board and still be
in the single-transistor-per-package realm.
I really don't think this would be all that tough to do with
discretes, either in terms of technical difficulty or board space
requirements.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
Then
there's a technical obstacle of bus driver chips that match Qbus
or Unibus specs. There just aren't any ideal choices that are available
now. There's an easy way around that, but then you're back to the
availability of time.
Those are exactly my issues. I've been wanting to make a QBUS
version of same for a long time now, and I certainly have the
skills, but my tuit supply is exhausted.
And the driver chips are a BIG problem. Probably the best
equivalents available now are the 74AS640 and 74AS760, but
they're really heavy hitters and would probably cause
unacceptable ringing on a really long bus. They'd most
likely be OK in a small QBUS enclosure, but I think a long
unibus system would be problematic. Anyone have any more
recent experience?
Nothing matches DEC's specs anymore, for probably obvious
reasons. The best I ever saw were some of the later NS
parts, which actually had an integrator on the output to
do slew-rate limiting. You could build something appropriate
out of discretes and op amps, but the amount of board space
you'd burn would murder you.