Modem control lines

I’m trying to detect the change of state of the modem control lines (CD, CTS, etc.) on a serial port under QNX6.2.

I know I can poll the state periodically but it would be better for me if the driver sends me a pulse (maybe on out of band data) when one of the lines change.

Is there any way to do this with the standard serial manager?

How hard would it be for me to modify the sources provided to get this functionality?

If you want use modem lines (RS-232,422,RTS,CTS) for transmit chars, then you must open with block mode flag.