16 Aug
2019
16 Aug
'19
10:05 p.m.
On Fri, Aug 16, 2019, 10:56 PM Ethan Dicks via cctalk <cctalk at classiccmp.org wrote:
On Sat, Aug 17, 2019 at 12:12 AM Charles via cctalk
<cctalk at classiccmp.org> wrote:
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
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.