25 Dec
2025
25 Dec
'25
7:36 p.m.
-----Original Message-----
From: Brent Hilpert <bhilpert(a)shaw.ca>
Sent: 25 December 2025 23:26
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk(a)classiccmp.org>
Cc: rob(a)jarratt.me.uk; 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:
50Z
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 - 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