A serial data link (10) includes a transmitter (12) using a differential transmitter cell (20) to transmit data using differential signals and a receiver (14) using a differential receiver cell (22) to receive differential signals. When the transmitter (12) is in a power-down state, the differential signals from the differential transmitter cell (20) are set to an illegal state that is detected by the receiver cell (22). Upon detecting the illegal state, unnecessary circuitry in the receiver (14) is shut off or placed in a low power state to conserve energy. When data transmission resumes, the receiver cell (22) automatically restores power to its circuitry and resumes receiving data.