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Xilinx Synthesis Technology User Guide

Xilinx Synthesis Technology User Guide

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XST <strong>User</strong> <strong>Guide</strong><br />

LOG File<br />

VHDL Code<br />

IO Pins Description<br />

Data Parallel Data Input Port (optional)<br />

ClkEn Clock Enable (optional)<br />

LeftRight Direction selection (optional)<br />

SerialInRight Serial Input Right for Bidirectional Shift Register<br />

(optional)<br />

PSO[x:0] Serial or Parallel Output<br />

The recognition of dynamic shift register happens on later synthesis<br />

steps. This is why no message about a dynamic shift register is<br />

displayed during HDL synthesis step. Instead you will see that an nbit<br />

register and a multiplexer has been inferred:<br />

...<br />

Synthesizing Unit .<br />

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

Found 1-bit 16-to-1 multiplexer for signal .<br />

Found 16-bit register for signal .<br />

Summary:<br />

inferred 16 D-type flip-flop(s).<br />

inferred 1 Multiplexer(s).<br />

Unit synthesized.<br />

...<br />

The notification that XST recognized a dynamic shift register is<br />

displayed only in the "Macro Statistics" section of the "Final Report".<br />

...<br />

...<br />

Macro Statistics<br />

# Shift Registers : 1<br />

# 16-bit dynamic shift register : 1<br />

Following is the VHDL code for a 16-bit dynamic shift register.<br />

2-70 <strong>Xilinx</strong> Development System

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