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Logically Determined Design: Clockless System Design with NULL Convention Logic by Karl Fant

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images CHAPTER 7 images

State Machines

In a logically determined system the state is expressed as spontaneously flowing wavefronts. Wavefront flow can be constrained in a ring to express the localized behavior of a state machine.

7.1 BASIC STATE MACHINE STRUCTURE

The basic structure of a logically determined state machine, illustrated in Figure 7.1, is a ring coupled to a pipeline through a combinational expression. The ring maintains the current state. The pipeline presents input wavefronts and accepts output wavefronts. The combinational expression receives the current state and the next data input and asserts the next state and a data output.

The ring must be initialized with one DATA wavefront expressing the initial state. If the ring is initialized to all NULL, there will be no current state wavefront for the first DATA wavefront, and the structure will deadlock. The ring will always contain exactly one DATA wavefront and one NULL wavefront.

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Figure 7.1 Basic state machine structure.

The combinational expression has a fan-in of two inputs and a fan-out of two, so the acknowledge signals completing its cycle have a fan-in of two and a fan-out of two. The completeness criterion of the combinational ...

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