reading the 232 port

[root]

I must be getting old, but I can't seem to figure out how to
do this.

I need to connect a device to my system's RS232 port and
under software control be able to detect the presence of a
signal (voltage) coming into the port.  The device generates
a 5+ volt pulse only and dosn't have anything fancy.

Can I simply open the port (/dev/ttyXX) and monitor for the
presence of a voltage on pin 3 (receive data) or do I need
to get more complicated?  I'm not a hardware type, but enjoy
tinkering.  Any software/hardware suggestions would be
appreciated.

Thanks
Scotty
{ames,rutgers,osu-cis,texsun,smu}!killer!ozdaltx!sysop