25 Oct
2016
25 Oct
'16
1:31 p.m.
On Oct 25, 2016, at 1:09 PM, Paul Koning
<paulkoning at comcast.net> wrote:
Maybe, but when you read section 5.2.7 of the PDP-11 Unibus specification:
Nine lumped ac loads reflect 20 precent, and 20 lumped ac loads reflect 40 percent of
a 25 ns risetime step.
On Oct 24, 2016, at 4:48 PM, Guy Sotomayor Jr
<ggs at shiresoft.com> wrote:
That seems more like a "for illustration" than an actual specification.
...
Where do you see the 25 ns spec? I didn't see it (admittedly in a quick scan).
5.2.7. It?s discussing the AC loading as a percentage of the risetime (25ns) to allow
for the
reflections. Yes, all I?m saying is that folks have been
looking at OMNIBUS and QBUS and those are
much simpler electrical environments than UNIBUS. You really need to pay attention to
the fact that UNIBUS is really a set of transmission lines so in addition to critical
levels
and currents you need to worry about the transmission line effects (ie the AC
components).
Sure. But whether you look at it as a transmission line or not, in the final analysis
there should be a small set of receiver and driver specs that matter. In theory, they
should be the ones listed in the DEC documents, neither more nor less. In practice, there
might be unspecified ones, such as max slew rate. If so, that's easy enough to handle
by introducing a suitable RC at the driver base (or gate).
As for the receiver, it seems that a TI 75140 (adjustable threshold line receiver) might
do the job.