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Xilinx maintains software libraries with thousands of functional design elements (primitives and macros) for different device architectures. New functional elements are assembled with each release of development system software. The catalog of design elements is known as the “Unified Libraries.” Elements in these libraries are common to all Xilinx device architectures. This “unified” approach means that you can use your circuit design created with “unified” library elements across all current Xilinx device architectures that recognize the element you are using.
Elements that exist in multiple architectures look and function the same, but their implementations might differ to make them more efficient for a particular architecture. A separate library still exists for each architecture (or architectural group) and common symbols are duplicated in each one, which is necessary for simulation (especially board level) where timing depends on a particular architecture.
If you have active designs that were created with former Xilinx library primitives or macros, you may need to change references to the design elements that you were using to reflect the Unified Libraries' elements.
The Libraries Guide describes the primitive and macro logic elements available in the Unified Libraries for the Xilinx FPGA and CPLD devices. Common logic functions can be implemented with these elements and more complex functions can be built by combining macros and primitives. Several hundred design elements (primitives and macros) are available across multiple device architectures, providing a common base for programmable logic designs.
This libraries guide provides a functional selection guide, describes the design elements, and addresses attributes, constraints, and carry logic.