Path: utzoo!attcan!uunet!cs.utexas.edu!samsung!umich!terminator!pisa.ifs.umich.edu!rees
From: rees@pisa.ifs.umich.edu (Jim Rees)
Newsgroups: comp.sys.apollo
Subject: Re: Help with getty and/or /etc/ttys at 10.2
Message-ID: <4d2de3e4.1bc5b@pisa.ifs.umich.edu>
Date: 3 Oct 90 16:31:25 GMT
References: <9010031349.AA05275@richter.mit.edu>
Sender: usenet@terminator.cc.umich.edu (usenet news)
Reply-To: rees@citi.umich.edu (Jim Rees)
Organization: University of Michigan IFS Project
Lines: 43

In article <9010031349.AA05275@richter.mit.edu>, krowitz@RICHTER.MIT.EDU (David Krowitz) writes:
  Most terminal cables
  are either wired for XON/XOFF handshaking with the following:
  
  pin1  -- pin1      frame ground
  pin2  -- pin3      transmit/receive
  pin3  -- pin2      receive/transmit
  pin7  -- pin7      signal ground

If you wire your cable this way, you lose the handshaking signals (the ones
that log you out when you hang up the phone, and hang up the phone when you
log out).

Pins 8 (DCD) and 20 (DTR) are the important ones.  So for a straight cable,
to go from a computer to a modem, we have

 2 --  2
 3 --  3
 7 --  7
 8 --  8
20 -- 20

and for a null modem cable, to go from a computer to a terminal,

 2 --  3
 3 --  2
 7 --  7
 8 -- 20
20 --  8

I've never used RTS/CTS handshaking, so I always wire 4 to 5 at each end:

 4 -   - 4
   |   |
 5 -   - 5

You could carry these signals through, but I've run across plenty of cases
where one end requires CTS and the other doesn't provide it, so it's safer
just to jumper them on each end unless you're connecting something (like a
printer) that requires these signals actually work.

Notice I didn't connect the frame grounds (pin 1).  In my opinion, these
should never be connected.  If you connect them you may get ground loops.