Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
Check out the Libraries Guide in your Xilinx documents folder. While the SR16RE is not directly available from VHDL, many other shift register types are. Perhaps you can use one of these alternative types. Otherwise, if you must have an SR16RE, your best choice is to create a simple project that implements one via schematic. Then in FPGA Editor turn this simple project into a macro. This macro can then be instantiated from VHDL as a "black box".