DEC bus transceivers

Guy Sotomayor Jr ggs at
Tue Oct 25 15:34:52 CDT 2016

> On Oct 25, 2016, at 12:40 PM, allison <ajp166 at> wrote:
>> Also, I think in a previous email you mentioned that the UNIBUS is 240ohm.  It’s not.
>> It’s 120ohm.
> My book says no. Qbus is for sure 120.
OK, re-reading the first part of section 5.2.5, it’s pretty clear that the Unibus is 120-ohm:
A bus terminator is defined as a Unibus element or part of an element containing
a resistive network which connects to the end of a Unibus segment and matches
the 120-ohm characteristic impedance of the Unibus transmission path.

Given that it’s hard to see that the impedance of the Unibus is anything but 120-ohms.

TTFN - Guy

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