Besides allowing the application to read directly the current state of DSR, CTS, DCD, and RI, the physical device driver has automatic modes that cause it to respond to the value that some input modem control signals can have:
These control modes are described in the section on States of the ASYNC Device Driver and in the IOCtls description. Additional information on the state of the input modem control signals is available by using the IOCtl ASYNC_GETCOMMEVENT.