3.2.2.2.2 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 9’s to any PINMMR control register, then the default functions are selected for the affected pads.
Each byte in a PINMMR control register is used to select the functionality for a given pad. If the application sets more than one bit within a byte for any pad, then the default function is selected for this pad.
Several bits in the PINMMR control registers are reserved and are not used to enable any functions. If the application sets only these bits and clears the other bits, then the default functions are selected for the affected pads.