Controlling Modem-Control Signals on Serial Port?

Controlling Modem-Control Signals on Serial Port?

Post by Todd Litw » Thu, 04 Aug 1994 09:23:34

Does anyone know how to read and write the modem-control signals on an SGI? I
am particularly interested in how to read and write the RTS, CTS, and CD lines
of an RS232 serial port. On a Sun this is done with ioctl() and the TIOCMBIS,
TIOCMBIC, and TIOCMGET arguments, but I have not been able to find references
in SGI's documentation on how to do this. Maybe I just haven't looked hard
enough. Does anyone have a pointer for me?
                Todd Litwin
                Jet Propulsion Laboratory
                (818) 354-5028


1. Controlling the serial port ??? (modem problems)

I have a very recalcitrant modem directly connected to the serial
port of an Indigo r4k (running 4.0.5F).

Sometimes (far too regularly :-() the comms application that we are
using over this line completes, but the modem then ends up in a strange
state and the modem lines aren't set correctly to allow another
incoming call.

Specifically, even if I power on/off the modem, unplug/plug the
serial cable, sometimes DTR never gets reasserted even when there is
a getty running on the port (/dev/ttyf2). This means the modem just
never answers an incoming call and just rings, rings, rings .....

The only way I've found to date to clear the problem is to turn the
machine off and power up again -- something I certainly am loath to
do every time.

So ..... can the individual lines of the serial port be controlled??
I'd like to have a small application such that if I detect that my modem
has screwed up yet again, I can simply toggle the input lines to some
sensible state.

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