25 Oct
2016
25 Oct
'16
1:36 p.m.
On Oct 25, 2016, at 4:31 PM, Guy Sotomayor Jr <ggs
at shiresoft.com> wrote:
That's my point. It says "a 25 ns risetime step". Not "THE 25 ns
risetime step". Nor "at the minimum 25 ns risetime step". So it seems to
be illustrative: if in your particular config the risetime happens to be that, the example
holds.
The obvious question to ask is what the bus capacitance is, between the module
contributions, and the distributed capacitance of the cable. That would explain (in
part) the risetime. The other part would be the inherent risetime of the TTL components
of the era, which are somewhere in that range judging by some of the old datasheets
I've just been looking at.
paul
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.