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Xilinx Synthesis Technology User Guide

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Decoders<br />

Log File<br />

HDL Coding Techniques<br />

A decoder is a multiplexer whose inputs are all constant with distinct<br />

one-hot (or one-cold) coded values. Please refer to the “Multiplexers”<br />

section of this chapter for more details. This section shows two<br />

examples of 1-of-8 decoders using One-Hot and One-Cold coded<br />

values.<br />

The XST log file reports the type and size of recognized decoders<br />

during the macro recognition step.<br />

Synthesizing Unit .<br />

Related source file is decoders_1.vhd.<br />

Found 1-of-8 decoder for signal .<br />

Summary:<br />

inferred 1 Decoder(s).<br />

Unit synthesized.<br />

==============================<br />

HDL <strong>Synthesis</strong> Report<br />

Macro Statistics<br />

# Decoders : 1<br />

1-of-8 decoder : 1<br />

==============================<br />

...<br />

The following table shows pin definitions for a 1-of-8 decoder.<br />

IO pins Description<br />

s[2:0] Selector<br />

res Data Output<br />

Related Constraints<br />

A related constraint is decoder_extract.<br />

VHDL (One-Hot)<br />

Following is the VHDL code for a 1-of-8 decoder.<br />

XST <strong>User</strong> <strong>Guide</strong> 2-83

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