On Fri, Aug 16, 2019, 10:56 PM Ethan Dicks via cctalk <cctalk@classiccmp.org> wrote:
> On Sat, Aug 17, 2019 at 12:12 AM Charles via cctalk > <cctalk@classiccmp.org> wrote: > > Is there any standard pinout for 20 ma current loop using a DB-25 > connector, > > analogous to the well-documents RS-232 serial interface? > > From checking a couple of devices, I don't think so. Here's how the > original IBM Async adapter for the 5150 did it... > > Pin 18 +receive current loop data > Pin 25 -receive current loop return > Pin 11 -transmit current loop data > Pin 9 +transmit current loop return > > One BlackBox adapter I found used different pins. > > > The ADM-3A receives on pins 23 & 25, and transmits on pins 24 & 17. > > I'm used to using 15 and 17 for sync serial clock. They are typically > NC for async. 23-25 have alternate uses that are, again, typically > NC. (I've never seen a device that used pin 25 for 'test'). There are > Sun workstations that have two serial ports over one DB25 which might > be the only use of the "B" pins I've encountered. > The DEC rainbow has B pins for talking to a modem dialer via a special cable... but it is basically useless for anything other than a few characters. Warner >
