35.6.4 SERCOM USART Synchronous Mode

Figure 35-6. Simplified USART Synchronous Mode Block Diagram
Note:
  1. In Synchronous USART Client Mode, USART - CTRLA.MODE = 0, USART RX/TX clock is supplied externally through input on SERCOM PAD[1], USART - CTRLA.TXPO = 0x0 or 0x3 from external remote USART device.
  2. In Synchronous USART Host Mode, USART - CTRLA.MODE = 1, USART RX/TX shift register clock sources are supplied internally from GCLK_SERCOMx_CORE and output on SERCOM PAD[1] to external remote USART device.