Pinout for current loop interface
charlesmorris800 at centurytel.net
Fri Aug 16 23:12:32 CDT 2019
Is there any standard pinout for 20 ma current loop using a DB-25 connector,
analogous to the well-documents RS-232 serial interface?
My PDP-8/A drives an ASR-33, and having just restored an ADM-3A I want to be
able to unplug the TTY and plug in the ADM.
I somewhat arbitrarily put the transmit data + on pin 2 and receive + on pin
3, and picked two uncommitted RS-232 pins for the - legs of both loops.
The ADM-3A receives on pins 23 & 25, and transmits on pins 24 & 17. Polarity
doesn't matter since both pairs use bridge rectifiers.
If this is some kind of de facto standard, I'll change the bulkhead
connector on the PDP-8 and the TTY to match.
Otherwise I'll just make yet another unique cable to hook up the ADM-3A to
the PDP-8 as it's wired.
Or would you recommend I use a different connector entirely? The reason I
used the DB-25 to begin with is that I had a DEC rack-mount plate that
already takes one.
Maybe a Jones 4-pin would make more sense.
thanks for any tips.
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