Peripherals such as USARTs and timers may be connected to I/O pins. Such peripherals will usually have a primary and optionally also alternate I/O pin connection, selectable by PORTMUX. By configuring and enabling such peripherals, the general-purpose I/O pin behavior normally controlled by PORT will be overridden by the peripheral in a peripheral-dependent way. Some peripherals may not override all of 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 which is not overridden by a peripheral will continue to operate as a general-purpose I/O pin.