> On Oct 24, 2016, at 1:41 PM, Paul Koning <paulkon...@comcast.net> wrote: > > >> On Oct 24, 2016, at 4:35 PM, Guy Sotomayor Jr <g...@shiresoft.com> wrote: >>> ... >> >> OK, I guess my last email didn’t make it. It appears to me that the rise >> time is set at 25ns. >> >> You need to look at the PDP-11 UNIBUS Design Description document on >> Bitsavers. Firstly, >> in section 4-1, it specifies which chips to use and recommends not using a >> whole list of other >> chips. The only recommended chips are: 8640, 8641 and 8881. > > Sure. But we're trying to understand what is required in order to design > alternatives. > > 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). TTFN - Guy
