Even or odd parity can be selected for error checking by writing 0x1 to the Frame Format bit field in the Control A register (CTRLA.FORM).

If *even parity* is selected (CTRLB.PMODE=0), the parity bit
of an outgoing frame is '1' if the data contains an odd number of bits that are '1', making
the total number of '1' even.

If *odd parity* is selected (CTRLB.PMODE=1), the parity bit
of an outgoing frame is '1' if the data contains an even number of bits that are '0',
making the total number of '1' odd.

When parity checking is enabled, the parity checker calculates the parity of the data bits in incoming frames and compares the result with the parity bit of the corresponding frame. If a parity error is detected, the Parity Error bit in the Status register (STATUS.PERR) is set.