The shortcut menu that appears when you click the arrow button on the right of the constant lists the clocks that appear in the Project Explorer window under the same FPGA target as the active VI. To use an FPGA clock that is not already in the project, first add the FPGA base clock, derived clock, or component-level IP (CLIP) clock to the Project Explorer window.

You also can specify an FPGA clock by clicking inside the constant and typing the name of the clock.

When creating a reusable subVI, use the FPGA clock control to specify an FPGA clock on the block diagram.