In this chapter we continue our treatment of signaling conventions by examining several signaling techniques that are specialized for particular circumstances.

Lossy interconnect, RC or LRC, is particularly demanding on a signaling convention. RC lines have a delay that increases quadratically with length and long tails to the step response that lead to intersymbol interference. Both of these problems can be addressed by using repeaters or by overdriving the line. LRC lines have frequency-dependent attenuation that leads to intersymbol interference at high signaling rates. This frequency-dependent attenuation can be canceled by equalization, which will significantly extend the maximum signaling rate for a particular line.

The effective pin and wire density of a signaling system can be doubled by using simultaneous bidirectional signaling to send bits simultaneously in both directions over a single transmission line. Bits travel in one direction on the forward-traveling wave and in the other direction on the reverse-traveling wave. The line is terminated at both ends to eliminate coupling between the two bit streams. This signaling convention introduces a new noise source cross talk between the forward- and reverse-traveling waves.

For AC-coupled lines it is necessary to band-limit the signal to remove its DC components, or the resulting DC offset will degrade margins. Encoding signals using nonoverlapping codes or running-disparity codes removes the DC component of the signal and has the added benefit of limiting the maximum run length of the signal.