> -----Original Message-----
> From: Brent Hilpert <[email protected]>
> Sent: 25 December 2025 23:26
> To: General Discussion: On-Topic and Off-Topic Posts
<[email protected]>
> Cc: [email protected]; Martin Bishop <mjd.bishop@emeritus-
> solutions.com>
> Subject: Re: [cctalk] Hot Video Shift Register on VT100
>
> On 2025Dec 25,, at 12:32 PM, Martin Bishop <mjd.bishop@emeritus-
> solutions.com> wrote:
> >
> > Series R on logic outputs are a classic "taming" mechanism, they also
> provide access to the net for more extreme measures (eg C to ground). Usu
> 22R or 33R close to the driver to bring the probable source impedance to
50Z
> - matching the nominal track impedance. The design may be evolved to
> include parallel (DC) termination or AC termination (series R & C) for
> multidrop loads. For 2025 circuits much of this is moot, the track
lengths are
> so short, in the 1980's it was different ...
> >
> > IBIS models for devices of interest and the wisdom of HoJo's oeuvre are
the
> classic references https://www.amazon.co.uk/High-Speed-Signal-Propagation-
> Advanced/dp/013084408X/ref=sr_1_1
>
> The series R/L in a signal line for parisitic oscillation/ringing
suppression
> actually goes back to the early tube days, well before logic, where they
can be
> found on tube grids, esp. power amps, even audio freq.
>From the responses I have had it sounds like my suspicion that later designs
added something to keep the part cool may well be correct. I will see if I
can insert a resistor by bending the CLK pin out of the socket (I have
spares if I break it) and see if I have a suitable resistor to hand.
Thanks
Rob
