PDP-8/I Negative-bus termination

[jim stephens]

On 5/5/2021 12:27 AM, Vincent Slyngstad via cctalk wrote:
> On 5/5/2021 12:03 AM, Josh Dersch via cctalk wrote:
>> Until this point I've never had any peripherals for my negibus systems
>> (apart from teletypes), and it occurs to me that I have no idea if 
>> the bus
>> needs to be terminated (and if so, with what).  There are 6 slots in the
>> RF08 backplane (D01-D06) for daisy-chaining to the next device, which is
>> where I assume they'd go; the RF08 manual does not make it clear what 
>> this
>> looks like or if it's actually required, and I've gone through the
>> available PDP-8/I docs and I'm still at a loss.
>>
>> Can anyone with negibus experience point me in the right direction?
>
> I don't have any actual Negibus gear except a TC01 (which I've yet to 
> be able to cable to anything), so I'm likely not the best expert.
>
> Regardless, my understanding is that it is terminated in basically the 
> same way as the positive bus, which is to say you stick a G717 in the 
> BAC connector that has the IOP and TS signals on it (at the far end of 
> the bus, of course).
>
this is Vince's site, (I think)

http://svn.so-much-stuff.com/svn/trunk/Eagle/projects/DEC/Gxxx/G717/

> This has the effect of terminating the signals that need to be 
> cleanest with 100 ohm resistors to ground.
>
> Not sure where I read that though, so I'm not able to easily double 
> check my memory.
>
>     Vince
>
Thanks
Jim