1. A semiconductor device for use in transmitting a signal over a conductive path to a receiver, the semiconductor device comprising: a semiconductor chip; a transmit circuit on the semiconductor chip; the transmit circuit to transmit a first sequence of signal levels representing bits to the receiver, where a rate of change of binary state in the bits in the first sequence represents a first frequency; the transmit circuit also to transmit a second sequence of signal levels representing bits to the receiver, where a rate of change of binary state in the bits in the second sequence represents a second frequency; circuitry to receive programming, the programming being responsive to measurement of the first and second sequences at the receiver.