18.3.2.2 Port Configuration
Use the Port Control (PORTx.PORTCTRL) register to configure the slew rate limitation for all the PORTx pins.
The slew rate limitation is enabled by writing a ‘1’ to the Slew Rate
         Limit Enable (SLR) bit in PORTx.PORTCTRL. Refer to the Electrical Characteristics
         section for further details.
