The SERCOM serial engine consists of a transmitter and receiver, baud-rate generator, and address matching functionality. The transmitter consists of a single write buffer and a shift register. The receiver consists of a two-levels receive buffer and a shift register. The baud-rate generator is capable of running on the GCLK_SERCOMx_CORE clock or an external clock.
The serial communication interface (SERCOM) can be configured to support a number of modes; I2C, SPI, and USART. Once configured and enabled, all SERCOM resources are dedicated to the selected mode.
The universal synchronous and asynchronous receiver and transmitter (USART) is one of the available modes in the Serial Communication Interface (SERCOM).
A data transmission is initiated by loading the DATA register with the data to be sent. The data in TxDATA is moved to the shift register when the shift register is empty and ready to send a new frame. When the shift register is loaded with data, one complete frame will be transmitted.
The Transmit Complete interrupt flag in the Interrupt Flag Status and Clear register (INTFLAG.TXC) is set and the optional interrupt is generated, when the entire frame plus stop bit(s) have been shifted out.
The DATA register should only be written when the Data Register Empty flag in the Interrupt Flag Status and Clear register (INTFLAG.DRE) is set, which indicates that the register is empty and ready for new data.
USART can generate DMA request when the transmit buffer (TX DATA) is empty. The request is cleared when DATA is written.
In this application SAM L22 Xplained pro board the EDGB CDC (SERCOM4) is utilized to select the mode of operation and user input string from the terminal.