On Sat, Aug 17, 2019 at 4:38 PM Noel Chiappa via cctalk <cctalk@classiccmp.org> 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. -tony