Differences Between XDC and UCF Constraints - 2023.2 English

ISE to Vivado Design Suite Migration Guide (UG911)

Document ID
UG911
Release Date
2023-11-01
Version
2023.2 English

The fundamental differences between XDC and UCF constraints are:

  • XDC is a sequential language, with clear precedence rules.
  • UCF constraints are typically applied to nets: XDC constraints are typically applied to pins, ports, and cell objects.
  • UCF PERIOD constraints and XDC create_clock command are not always equivalent and can lead to different timing results.
  • UCF by default does not time between asynchronous clock groups, while in XDC, all clocks are considered related and timed unless otherwise constrained (set_clock_groups).
  • In XDC, multiple clocks can exist on the same object.