16.3.2.4 Peripheral Override

Peripherals such as USARTs, ADCs and timers may be connected to I/O pins. Such peripherals will usually have a primary and, optionally, one or more alternate I/O pin connections, selectable by PORTMUX or a multiplexer inside the peripheral. By configuring and enabling such peripherals, the general purpose I/O pin behavior normally controlled by PORT will be overridden in a peripheral dependent way. Some peripherals may not override all the PORT registers, leaving the PORT module to control some aspects of the I/O pin operation.

Refer to the description of each peripheral for information on the peripheral override. Any pin in a PORT that is not overridden by a peripheral will continue to operate as a general purpose I/O pin.