Handshaking circuits are provided in a communications cable and in a device operable to be mated with the communications cable. Before a device can utilize the power supply signal of such a communications channel, the two handshaking circuits must sufficiently identify one another over a power supply signal with a decreased voltage. The decreased voltage allows for a cable plug to be provided with a safe, protected power that cannot cause harm to a human. The decreased voltage also reduces the chance that a device can receive a primary power supply signal from the cable before the device sufficiently identifies itself. Accordingly, a laptop may be connected to a portable music player, but the voltage of the power supply signal provided by the laptop to the cable may be decreased on-cable until the handshaking circuit of the portable music player sufficiently performs a handshaking operation with a on-cable handshaking circuit.