Abstract: A system includes a driver device configured to transmit a first signal through a communication line to a device that is external to the system; wherein the communication line is configured to (i) receive signals from the system and to transmit signals to the system, and (ii) receive signals from the device that is external to the system and to transmit signals to the device that is external to the system; a reference device configured to generate a reference value; and a receiver configured to: receive, through the communication line, a second signal affected by an output from the device that is external to the system; and determine a logic state of the device external to the system based on: a value associated with the second signal on the communication line; a value associated with the first signal transmitted by the driver device; and the reference value.