DEC bus transceivers

Guy Sotomayor Jr ggs at
Mon Oct 24 15:48:16 CDT 2016

> On Oct 24, 2016, at 1:41 PM, Paul Koning <paulkoning at> wrote:
>> On Oct 24, 2016, at 4:35 PM, Guy Sotomayor Jr <ggs at> 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

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

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