driving cells and port loads

The external driver that drives an input port has impedance and parasitic load characteristics that can affect the signal timing. To more accurately take these effects into account, you can use the set_driving_cell cmd. This cmd specifies the name of a library cell that is presumed to be driving the input port. Using a library cell as a driver allows PT to more accurately calculate the port delay times and transition times, especially for library cells having delays with nonlinear dependence on capacitance.

You can use the set_load cmd to specify the amount of capacitance on a port or net, allowing PT to more accurately calculate the effects of the load on port or net delay.