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Xilinx Synthesis Technology User Guide

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Inputs<br />

Next<br />

State<br />

Function<br />

RESET<br />

CLOCK<br />

State<br />

Register<br />

Only for Mealy Machine<br />

HDL Coding Techniques<br />

Output<br />

Function<br />

Outputs<br />

X8993<br />

For HDL, process (VHDL) and always blocks (Verilog) are the most<br />

suitable ways for describing FSMs. (For description convenience<br />

<strong>Xilinx</strong> uses "process" to refer to both: VHDL processes and Verilog<br />

always blocks).<br />

You may have several processes (1, 2 or 3) in your description,<br />

depending upon how you consider and decompose the different<br />

parts of the preceding model. Following is an example of the Moore<br />

Machine with Asynchronous Reset, “RESET”.<br />

• 4 states: s1, s2, s3, s4<br />

• 5 transitions<br />

• 1 input: "x1"<br />

• 1 output: "outp"<br />

This model is represented by the following bubble diagram:<br />

XST <strong>User</strong> <strong>Guide</strong> 2-173

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