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Xilinx Synthesis Technology User Guide

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

Log File ...............................................................................2-25<br />

Related Constraints ............................................................2-25<br />

Latch with Positive Gate .....................................................2-26<br />

Latch with Positive Gate and Asynchronous Clear .............2-27<br />

4-bit Latch with Inverted Gate and Asynchronous Preset ........2-29<br />

VHDL Code .........................................................................2-29<br />

Verilog Code .......................................................................2-30<br />

Tristates ........................................................................................2-31<br />

Log File ....................................................................................2-31<br />

Related Constraints .................................................................2-31<br />

Description Using Combinatorial Process and Always Block ..2-32<br />

VHDL Code .........................................................................2-33<br />

Verilog Code .......................................................................2-33<br />

Description Using Concurrent Assignment ..............................2-34<br />

VHDL Code .........................................................................2-34<br />

Verilog Code .......................................................................2-34<br />

Counters ........................................................................................2-35<br />

Log File ....................................................................................2-36<br />

4-bit Unsigned Up Counter with Asynchronous Clear ..............2-36<br />

VHDL Code .........................................................................2-37<br />

Verilog Code .......................................................................2-38<br />

4-bit Unsigned Down Counter with Synchronous Set ..............2-39<br />

VHDL Code .........................................................................2-39<br />

Verilog Code .......................................................................2-40<br />

4-bit Unsigned Up Counter with Asynchronous Load from Primary Input<br />

2-40<br />

VHDL Code .........................................................................2-40<br />

Verilog Code .......................................................................2-41<br />

4-bit Unsigned Up Counter with Synchronous Load with a Constant 2-<br />

42<br />

VHDL Code .........................................................................2-42<br />

Verilog Code .......................................................................2-43<br />

4-bit Unsigned Up Counter with Asynchronous Clear and Clock Enable<br />

2-43<br />

VHDL Code .........................................................................2-43<br />

Verilog Code .......................................................................2-44<br />

4-bit Unsigned Up/Down counter with Asynchronous Clear ....2-45<br />

VHDL Code .........................................................................2-45<br />

Verilog Code .......................................................................2-46<br />

4-bit Signed Up Counter with Asynchronous Reset .................2-46<br />

VHDL Code .........................................................................2-47<br />

Verilog Code .......................................................................2-48<br />

Accumulators ................................................................................2-49<br />

Log File ....................................................................................2-50<br />

4-bit Unsigned Up Accumulator with Asynchronous Clear ......2-50<br />

VHDL Code .........................................................................2-51<br />

Verilog Code .......................................................................2-52<br />

Shift Registers ...............................................................................2-52<br />

Log File ....................................................................................2-55<br />

Related Constraints .................................................................2-55<br />

x <strong>Xilinx</strong> Development System

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