24.3.2.4.1 Receiving Frames

The receiver starts data reception when it detects a valid Start bit. Each bit that follows the Start bit will be sampled at the baud rate or XCK clock, and shifted into the Receive Shift register until the first Stop bit of a frame is received. A second Stop bit will be ignored by the receiver. When the first Stop bit is received and a complete serial frame is present in the Receive Shift register, the contents of the Shift register will be moved into the receive buffer. The receive complete interrupt flag (RXCIF in USARTn.STATUS) is set, and the optional interrupt is generated.

The receiver buffer can be read by reading RXDATA, comprising of DATA[7:0] in USARTn.RXDATAL, and DATA[8] in USARTn.RXDATAH. RXDATA should not be read unless the Receive Complete Interrupt Flag (RXCIF in USARTn.STATUS) is set. When using frames with fewer than eight bits, the unused Most Significant bits are read as zero. If 9-bit characters are used, the ninth bit (DATA[8] in USARTn.RXDATAH) must be read before the low byte (DATA[7.0] in USARTn.RXDATAL).