Logically Determined Design: Clockless System Design with NULL Convention Logic

CHAPTER 3

The Structure of Logically Determined Systems

The structure of a logically determined system is quite different from a clock-driven system. While a clocked system derives its liveness and coordination of information flow from the pulse of the clock, a logically determined system must derive these properties of behavior solely from its logical relationships.

It is first shown that there is a simple logical relationship that is inherently live. It is next shown that this inherently live logical relationship can be evolved into structures called cycles, which can be composed into pipelines that spontaneously propagate data wavefronts. These pipelines can then be composed into structures that coordinate the flow and interaction of data wavefronts implementing complex digital systems.

3.1 THE CYCLE

There is one very simple logical relationship that is spontaneously active.

3.1.1 The Ring Oscillator

A ring oscillator shown in Figure 3.1 is a closed signal path with an odd number of inversions propagating a binary signal. It will continually strive to oscillate and is spontaneously active.

Figure 3.1 Ring oscillator.

3.1.2 Oscillator Composition with Shared Completeness Path