On 10/25/2016 03:36 PM, Eric Smith wrote:
On Tue, Oct 25, 2016 at 2:09 PM, Paul Koning <paulkon...@comcast.net> wrote:
As for the receiver, it seems that a TI 75140 (adjustable threshold line
receiver) might do the job.
The high-level input current spec on that is max 100uA, which exceeds the
DEC specification.
One thing everyone seems to be ignoring is that the DEC leakage current
specifications are for Vcc from 0V to 5.25V. In other words, Unibus devices
can't load the bus more when they're not powered. Almost all proposed
alternatives to the DEC-recommended chips do not meet that requirement.
I believe this is a holdover from the PDP-8 days. I do not
know of any PDP-11 system that would actually tolerate a
Unibus peripheral being powered down in the middle of the
bus. I am pretty sure that due to the bus grant logic
present on nearly every peripheral controller, that powering
it down would jam the bus.
So, I suspect that for a PDP-11 or VAX Unibus system, this
requirement does not really make much sense.
Jon
