>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.

I believe there was a time when the Apple recommended Hardware Handshake 
cable had CTS tied to DTR, and some modem companies still deliver this 
configuration.  US Robotics is one I think.  The current Apple 
recommended Hardware Handshake cable has RTS tied to DTR, and this is the 
cable you'll most likely get from places like Best Buy, Compu USA and 
most modem manufacturers.  In an ideal world one signal is used for 
in-bound flow control and the other is used for out-bound flow control.  
As Dave says, the Mac can only support one, not both. And just like Dave 
I can't remember if RTS is in-bound or out-bound, but disabling DTR might 
just solve you disconnection problem.

-bob