> 
> On Tue, 1 Apr 1997, Jon Lefman wrote:
> > Thanks for the response.  I understand crtscts and mdmbuf, but why should
> > my modem ignore change in dtr?  Would dtr ever drop when using pppd?
> 
> The Mac serial ports only have one "handshake out" pin; most of the cables
> I've seen wire that pin to both DTR and RTS (or is it CTS? I always
> confuse those two :) In any case, unless you set your modem to ignore DTR
> (at&d0, usually), there's a chance that it'll hang up when you don't want
> it to. Alternatively, you could increase the value of some S register that
> specifies how long DTR must be low before the modem hangs up, although
> there'd still be the chance of an accidental disconnection.

You've hit on one problem w/ the mac's serial ports. There's only one
output. The question is do we use it as DTR (which will tell the modem
to hang up the phone), or do we use it for flow control (telling the
modem to shut up).

Right now, if you set crtscts, the mac will listen to CTS, and use the
output to tell the modem to hang up. If you set mdmbuf, the computer
will use DTR to say when the other side should shut up,, and listen
to DCD for when to send or not.

All that's the way it should be. Now, if you set both, you get a mut
mode (done deliberately) so that DTR is used as outgoing flow control
(tell the other side to shut up) and CTS is listen to to shut up the mac.

Hopefully that will change in a month, so be forwarned! When the change
happens, setting both crtscts and mdmbuf will do some mix of both.
Setting cdtrcts will give full-duplex flow control.

You have been warned.

Take care,

Bill