Registers and Bits

Table 1. Register and Bit Mnemonics
Symbol Description
R/W Read/Write accessible register bit. The user can read from and write to this bit.
R Read-only accessible register bit. The user can only read this bit. Writes will be ignored.
W Write-only accessible register bit. The user can only write this bit. Reading this bit will return an undefined value.
BIT Bit names are shown in uppercase. (Example ENABLE)
FIELD[n:m] A set of bits from bit n down to m. (Example: PINA[3:0] = {PINA3, PINA2, PINA1, PINA0}

Reserved bits are unused and reserved for future use. For compatibility with future devices, always write reserved bits to zero when the register is written. Reserved bits will always return zero when read.

Reserved bit field values must not be written to a bit field. A reserved value won't be read from a read-only bit field.

PERIPHERALi If several instances of a peripheral exist, the peripheral name is followed by a number to indicate the number of the instance in the range 0-n. PERIPHERAL0 denotes one specific instance.
Reset Value of a register after a power Reset. This is also the value of registers in a peripheral after performing a software Reset of the peripheral, except for the Debug Control registers.
SET/CLR Registers with SET/CLR suffix allows the user to clear and set bits in a register without doing a read-modify-write operation. These registers always come in pairs. Writing a one to a bit in the CLR register will clear the corresponding bit in both registers, while writing a one to a bit in the SET register will set the corresponding bit in both registers. Both registers will return the same value when read. If both registers are written simultaneously, the write to the CLR register will take precedence.