14 May
2015
14 May
'15
5:21 p.m.
Dave,
Thanks a million! I did not know that. As for the receivers, it can go into
straight TTL apparently, I read that somewhere in an HP manual.
Marc
From: "J. David Bryan" <jdbryan at
acm.org>
> ...where to get the older CTuL logic IC bus drivers (the 9956 in
> particular) besides from old boards?
With the inclusion of a pulldown resistor to -2V, the
TI SN75121 is a
recommended replacement, per page 5-6 of the
"HP 1000 M/E/F-Series Computers I/O Interfacing
Guide" (02109-90006
September 1980). It's an active part:
14 May
14 May
10:52 p.m.
On Thursday, May 14, 2015 at 14:21, Marc Verdiell wrote:
Thanks a million!
You're welcome.
As for the receivers, it can go into straight TTL
apparently, I read
that somewhere in an HP manual.
Both TTL and LSTTL (but not STTL or HTTL) will work with an appropriate
pulldown resistor. LSTTL is recommended for the lower power and improved
speed over TTL. The pulldowns are necessary to guarantee logic zeros when
driven by the original CTuL or newer 75121 parts, which have open-emitter
outputs.
Section 5-7, "Computer Backplane Assembly Requirements," of the
aforementioned interfacing manual details the recommended circuits.
-- Dave
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