Description:

The FireCracker (CM17A) is a send-only X10 controller that connects to
a serial port and transmits commands via RF to X10 transceivers.

The FireCracker derives its power supply from either the RTS or DTR
signals from the serial port. At least one of these signals must be
high at all times to ensure that power is not lost from the
FireCracker. The signals are pulsed to transmit a bit (DTR for '1' and
RTS for '0'). The normal rx/tx read/write lines are not used by the
device - but are passed through to allow another serial device to be
connected (as long as it does not require hardware handshaking).