Pinout for current loop interface
imp at bsdimp.com
Sat Aug 17 00:05:05 CDT 2019
On Fri, Aug 16, 2019, 10:56 PM Ethan Dicks via cctalk <cctalk at classiccmp.org>
> On Sat, Aug 17, 2019 at 12:12 AM Charles via cctalk
> <cctalk at classiccmp.org> wrote:
> > Is there any standard pinout for 20 ma current loop using a DB-25
> > 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
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