Logically Determined Design: Clockless System Design with NULL Convention Logic

CHAPTER 8

Busses and Networks

Data path wavefronts are steered through a logically determined system by interacting with control wavefronts. The basic fan-out and fan-in steering structures have already been presented in Section 3.3 of Chapter 3. This chapter will elaborate on larger structures built from those basics.

8.1 THE BUS

8.1.1 The Serial Bus Structure

A bus steers wavefronts from multiple source paths to multiple destination paths. The most familiar form is the serial bus over which one wavefront can flow at a time. Figure 8.1 shows a serial bus with two source paths and five destination paths. The two source paths fan-in to a single path, which then fans-out to the five destination paths. The source registration stages are controlled by a single 2 value control variable. The destination registration stages are controlled by a single 5 value control variable. The Nth data wavefront will be steered by the Nth source control variable and the Nth destination control variable.

The throughput of a serial bus can be increased with 2D pipelining. Several wave-fronts can simultaneously flow through the bus as the control variables propagate across the data path. As with most 2D pipelined structures, the throughput of the bus will be independent of the width of the data path. A ...