Described are communication systems that convey differential and common-mode signals over the same differential channel. Noise-tolerant communication schemes use low-amplitude common-mode signals that are easily rejected by differential receivers, thus allowing for very high differential data rates. Some embodiments employ the common-mode signals to transmit backchannel signals for adjusting the characteristics of the differential transmitter. Backchannel control signals are effectively conveyed even if the forward channel transmitter is so maladjusted that the received differential data is unrecognizable. Systems in accordance with the above-described embodiments obtain these advantages without additional pins or communications channels, and are compatible with both AC-coupled and DC-coupled communications channels. Data coding schemes and corresponding data recovery circuits eliminate the need for complex, high-speed CDR circuits.