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Xilinx Synthesis Technology User Guide

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FPGA Optimization<br />

• Tristates<br />

This group contains all the tristate primitives, namely the BUFT.<br />

• Clock Buffers<br />

This group contains all the clock buffers, namely BUFG, BUFGP,<br />

BUFGDLL.<br />

• IO Buffers<br />

This group contains all the standard I/O buffers, except the clock<br />

buffer, namely IBUF, OBUF, IOBUF, OBUFT, IBUF_GTL ...<br />

• LOGICAL<br />

This group contains all the logical cells primitives that are not<br />

basic elements, namely AND2, OR2, ...<br />

• OTHER<br />

This group contains all the cells that have not been classified in<br />

the previous groups.<br />

The following section is an example of an XST report for cell usage:<br />

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

...<br />

Cell Usage :<br />

# BELS : 70<br />

# LUT2 : 34<br />

# LUT3 : 3<br />

# LUT4 : 34<br />

# FlipFlops/Latches : 9<br />

# FDC : 8<br />

# FDP : 1<br />

# Clock Buffers : 1<br />

# BUFGP : 1<br />

# IO Buffers : 24<br />

# IBUF : 16<br />

# OBUF : 8<br />

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

XST <strong>User</strong> <strong>Guide</strong> 3-21

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