Subject: Re: pppd's cdtrcts option is broken!
To: Frederick Bruckman <>
From: Bill Studenmund <>
List: current-users
Date: 09/04/1998 13:04:58
On Fri, 4 Sep 1998, Frederick Bruckman wrote:

> On Fri, 4 Sep 1998, Bill Studenmund wrote:
> > What options do you have on the /etc/ttys line for tty00? I didn't think
> > that chat asserted crtscts...
> I have tty00 turned off in /etc/ttys.

Good. Except that even if the tty is off, the line settings at the end of
the line, if present, still matter. So if you had "rtscts" as an option
latter on that line, it'd get applied every time the port is opened.

> I was surprised at first, too. Upon reflection, I think it may in fact be
> desirable for chat to work that way. AFAIK, all modems >=28,800 power up
> with hardware handshaking enabled. The point is not worth pressing, since
> it's practically impossible to overflow your buffers while the modem is in
> command mode.
> In fact, I've found that you can take a mac68k box (with its goofy serial
> port), a "hardware handshaking" cable (that ties DTR to RTS), and set up
> pppd with 'crtscts', practically oblivious to the problem. Since "DTR off"
> typically isn't sensed for .05 to .06 seconds (settable via S25), the
> modem doesn't actually hang up except on long file transfers.

s/crtscts/cdtrcts/ and you're right. crtscts doesn't ever de-assert an
input flow control line (like RTS in a normal RS/232 port). DTR, in that
case, is only used to hang up the modem.

Take care,