Pinout for current loop interface

Tony Duell ard.p850ug1 at
Sat Aug 17 10:55:56 CDT 2019

On Sat, Aug 17, 2019 at 4:38 PM Noel Chiappa via cctalk
<cctalk at> wrote:
>     > From: Charles Morris
>     > Is there any standard pinout for 20 ma current loop using a DB-25
>     > connector, analogous to the well-documents RS-232 serial interface?
>     > ...
>     > Or would you recommend I use a different connector entirely? .. Maybe a
>     > Jones 4-pin would make more sense.
> I've never heard of people using DB25 for 20mA, at least historically,
> contemporaneous with its widespread actual use. E.g. DEC universally used
> 'flat' 8-pin Mate-n-Lok connectors for 20mA serial connections.

Looking around here I think it is safe to say that there is no
standard. I've got :

3 different wirings on DB25 connectors (the IBM PC serial port which has already
been mentioned, the original Apple ][ bitbanger serial card and a Miniterm 1203
portable terminal which can be strapped internally to put a current
loop interface
on pins 13-16 of the DB25). In all cases there's a subset of the RS232
interface on
the expected pins

Those flat 8-pin mate-n-lock connectors that DEC used

An 8 pin mini-Jones connector (Intellec 8)

DE9 (on a 'Ferret' peripheral tester thing) And a different wiring
on a cable that came with my Data Dynamics 390 (Teletype
Model 33 mechanical parts with Data Dynamics electronics)

5 pin 240 degree DIN socket (on an acoustic modem)

GPO Plug 420/Jack 84 (or Jack 95). This is the old 4 contact
cylindrical plug/socket used on UK telephone systems in the
1960s/1970s and seems to be used for current loop by UK
universities at the time.

Screw terminal barrier strips.


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