Pinout for current loop interface

Ethan Dicks ethan.dicks at
Sat Aug 17 15:26:45 CDT 2019

On Sat, Aug 17, 2019 at 12:14 PM Charles via cctalk
<cctalk at> wrote:
> >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.
> Thanks for the comments... I asked mostly because the ADM-3A has both RS-232
> and current loop interfaces built-in

Given the problem you are trying to solve, if I were in your shoes,
since I have a lot of DEC gear, I would standardize on 8-pin
Mate-n-Lok connectors, but I have numerous devices already so equipped
(ASR33, VT52, VT220, VT100 w/20mA option, PDP-8 (various), DZ11
breakout panel...)  Since I was just holding an original IBM PC serial
interface (as discussed above), I should probably bite the bullet and
make a DB25-8-pin-Mate-n-Lok cable for it, just in case (I happen to
have a couple of options for using ISA cards on Amigas, so it's even

I happen to have a stash of the shells.  What I should do is buy a bag
of the pins and get a reel of the 4-wire (R/G/B/W) cable that was
commonly used in the DEC world, then I'd be all set.

DB25s are easier to come by, but as has been mentioned, there's not
one way to wire them up and having a large stack of magic pin-swabber
cables is kind of a pain.


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