DEC bus transceivers

David Bridgham dab at
Mon Oct 24 15:56:10 CDT 2016

On 10/24/2016 04:30 PM, Paul Koning wrote:

> I don't see any max slew rate spec in the driver specs in the peripherals handbook.

For the QBUS from the PDP11 Bus Handbook 1979, page 125:

AC Specifications
Bus driver output pin capacitive load: Not to exceed 10 pF
Propagation delay: Not to exceed 35 ns
Skew (difference in propagation time between slowest and fastest
gate): Not to exceed 25 ns
Rise/Fall Times: Transition time from 10% to 90% for positive
transition, and from 90% to 10% for negative transition, must
be no faster than 10 ns and no slower than 1 us

It's faster than the Unibus (that Guy posted) presumably because QBUS
systems tend to be much smaller but a driver that meets the Unibus spec
is good on the QBUS too.

On the receiver, maybe the way to go would be a linear comparator.  It
would be easy enough to come up with a 1.5V rail (half way between the
1.3V low and 1.7V high levels) running down the length.  And you have to
look but you can find them with a fast enough propagation speed.  The
only thing I'm not seeing is meeting the 10pF capacitive load; the spec
sheets just don't say.


More information about the cctalk mailing list