DEC bus transceivers

Christian Corti cc at
Tue Oct 25 04:25:35 CDT 2016

On Mon, 24 Oct 2016, Paul Koning wrote:
>> 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).

I have the 1979 edition of the PDP11 Bus Handbook in front of me. This 
book is very handy as all information on the Unibus and QBUS can be found 
there. The driver and receiver characteristics are listed in table 1-3 on 
page 60. The only timing parameters for the drivers are the maximum
_propagation_ delays (25ns TPDL and 35ns TPDH), so I interprete this that 
the drivers can be faster than that, and no single word about slew rates.
For the QBUS drivers, page 125 specifies the rise/fall times: 10ns<=t<=1µs
There is no such equivalent for the Unibus.


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