1. A semiconductor device comprising: a semiconductor chip; a transmitter on the semiconductor chip, the transmitter to convey a serial, differential signal over a channel to a receiver; the transmitter further having circuitry to receive a sequence of input bits and to responsively generate the serial, differential signal to have signal levels, in a manner that a signal level corresponding to a given one of the input bits in the sequence is attenuated when the given one of the input bits has a same state as an adjacent input bit in the sequence, relative to when the given one of the input bits does not have the same state as the adjacent input bit, wherein a degree of attenuation is selective; and circuitry to cause the transmitter to transmit a bit pattern to the receiver to responsively select the degree of attenuation.