AR# 64052


Using Vivado Simulation Libraries - UNISIM Library


When you instantiate a component in your design, the simulator must reference a library that describes the functionality of the component to ensure proper simulation.

The Xilinx libraries are divided into categories based on the function of the model.

You must specify different simulation libraries according to the simulation points.

This article describe the UNISIM library in more detail.


The UNISIM library is used in functional simulation and behavioral simulation when the RTL instantiates device primitives.

The VHDL UNISIM library is located at <Vivado_Install_Dir>/data/vhdl/src/unisims.
It is divided into the following files, which specify the primitives for the Xilinx device families:
  • The component declarations (unisim_VCOMP.vhdp)
  • Package files (unisim_VPKG.vhd)
To use these primitives, place the following two lines at the beginning of each file:

library UNISIM;
use UNISIM.Vcomponents.all;

You must also compile the library and map the library to the simulator.
The method depends on the simulator.

Verilog UNISIM Library
The Verilog UNISIM library is located at <Vivado_Install_Dir>/data/verilog/src/unisims.
In Verilog, the individual library modules are specified in separate HDL files.

This allows the -y library specification switch to search the specified directory for all components and automatically expand the library.

The Verilog UNISIM library does not have to be specified in the HDL file prior to using the module.

Verilog is case-sensitive, so ensure that UNISIM primitive instantiations adhere to an uppercase naming convention, for example, BUFG.
If you use precompiled libraries, use the correct simulator command-line switch to point to the precompiled libraries.

The following is an example for the Vivado simulator:

-L unisims_ver

Linked Answer Records

Master Answer Records

Answer Number Answer Title Version Found Version Resolved
58895 Xilinx Simulation Solution Center - Design Assistant - Simulation Libraries - UNISIM & SIMPRIM N/A N/A
AR# 64052
Date 04/09/2015
Status Active
Type General Article
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