4.3.2 General Rules for Multiplexing Control Registers
The PINMMR control registers can only be written in privileged mode. A write in a nonprivileged mode will generate an error response.
If the application writes all 0s to any PINMMR control register, then the default functions are selected for the affected pins.
Each byte in a PINMMR control register is used to select the functionality for a given pin. If the application sets more than 1 bit within a byte for any pin, then the default function is selected for this pin.
Some bits within the PINMMR registers could be associated with internal pads that are not brought out in the 100-pin package. As a result, bits marked reserved should not be written as 1.