User Constraint Files (UCF) are a proprietary file format from Xilinx for constraining a hardware design. UCF files are not supported in Xilinx Vivado. The replacement format is called Xilinx Design Constraints (XDC).

User Constraint Files (UCF) are a proprietary file format from Xilinx for constraining a hardware design. UCF files are used by Xilinx ISE tools for timing and physical constraints. UCF files are saved as:
- *.ucf (user constraints)
- *.xcf (XST synthesis constraints)
- *.ncf (netlist constraints)

UCF files are not supported in Xilinx Vivado. The replacement format is called Xilinx Design Constraints (XDC), a scripting language (TCL) based syntax.

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