ATMEL_US_USCLKS
ATMEL_US_USCLKS | ATMEL_US_USMODE);
mode &= ~ATMEL_US_USCLKS;
mode &= ~(ATMEL_US_USCLKS | ATMEL_US_NBSTOP | ATMEL_US_PAR);
#define ATMEL_US_USCLKS_MCK FIELD_PREP(ATMEL_US_USCLKS, 0)
#define ATMEL_US_USCLKS_MCK_DIV8 FIELD_PREP(ATMEL_US_USCLKS, 1)
#define ATMEL_US_USCLKS_GCLK FIELD_PREP(ATMEL_US_USCLKS, 2)
#define ATMEL_US_USCLKS_SCK FIELD_PREP(ATMEL_US_USCLKS, 3)