Example: Disable Impossible Paths

In this example, special control logic exists for LUT2 and FF2. Therfore, the path from FF1 to FF2 though LUT2 can be ignored by timing analysis.

Figure 1. Set a False Path Example

SDC Commands

set_false_path -from [get_pins {FF1|CLK}] -through [get_cells LUT2] -to [get_pins {FF2|D]

In another example, a group of flipflops, FF1[3:0], use a naming pattern and the same connection as the FF1 flipflop in the previous example. In this case you can use a wildcard with the set_false_path command to constrain the whole group.

Figure 2. Set a False Path for a Bus Example

SDC Commands

set_false_path -from [get_pins {FF1[*]|CLK}] -through [get_cells LUT2] -to [get_pins {FF2|D]