Eric Smith wrote:
Don North wrote:
Alternatively google for 'Am26s10cn'. It
is about the closest to a
true unibus transceiver that is still available (in a DIP package even).
TI makes it, available from DigiKey.
Unfortunately the max Vil and min Vih for the 26S10 are significantly
different than the DEC specs. For a small system you might be able to
get away with using it, but noise immunity and general reliability
will be worse.
Eric
This is all well understood, and discussed in detail in the CCtech
thread from a couple
of years ago that I referenced. As part of the discussion I did an input
vs output
comparison of the two parts:
http://www.ak6dn.com/stuff/26S10vs8641.jpg
The 26s10 has an input threshold of 2.0V +/- 0.25V, where the original
DS8640/41 had an
input threshold of 1.5V +/- 0.2V. UNIBUS terminates all the bussed
signals to 3.5V, so
you indeed lose 0.5V of high side noise margin using the 26s10 vs an
8641 (but you also
gain 0.5V of low side margin). Indeed, with the 26s10 the high and low
margins are now
symmetric (3.5-2.0=1.5; 2.0-0.5=1.5); with the original 8641 they were
very asymmetric
(3.5-1.5=2.0; 1.5-0.5=1.0).
The 26s10 is also faster, both in terms of Tpd and edge rate compared to
the older device.
So for very long UNIBUSes, this may present more of a problem with
reflections.
But the botom line is the DS864X parts are essentialy unobtanium,
whereas you can buy
the 26s10 parts (still made by TI) from DigiKey today for a very
reasonable price (~$1).
Don