Input/Output Files

The Constraints Editor requires a User Constraints File (UCF) and a Native Generic Database (NGD)file as inputs. The Constraints Editor used the NGD to provide names of logical elements for grouping. As output, it uses the UCF, including the changes made with the Constraints Editor.

After you open the Constraints Editor you must first open a UCF file. If the UCF and NGD root names are not the same, you must select the appropriate NGD file to open. For details on loading files, see the “Loading Files” section in the "Using the Constraints Editor" chapter.

Upon successful completion, the Constraints Editor writes out a UCF. NGDBuild (translation)uses the UCF, along with design source netlists, to produce an NGD file. The NGD file is read by the MAP program. MAP generates a physical design database in the form of an NCD (Native Circuit Description) file and also generates a PCF (Physical Constraints File). The implementation tools use these files to ultimately produce a bitstream. See the “Constraints Editor Flow” figure.

Figure 1.7 Constraints Editor Flow

In this software release, not all Xilinx constraints are accessible through this GUI. Constraints supported in the GUI and the associated UCF syntax are described in the “UCF Syntax” appendix.