The SERCOM must be configured to the desired mode by writing the Operating Mode bits in the Control A register (CTRLA.MODE) as shown in the table below.

Table 1. SERCOM Modes
CTRLA.MODE Description
0x0 USART with external clock
0x1 USART with internal clock
0x2 SPI in client operation
0x3 SPI in host operation
0x4 I2C client operation
0x5 I2C host operation
0x6-0x7 Reserved

For further initialization information, see the respective SERCOM mode chapters: