Texas Instruments MSP430x1xx manual Usart Receive Enable, 5. State Diagram of Receiver Enable

USART Operation: UART Mode

13.2.4 USART Receive Enable

The receive enable bit, URXEx, enables or disables data reception on URXDx as shown in Figure 13−5. Disabling the USART receiver stops the receive operation following completion of any character currently being received or immediately if no receive operation is active. The receive-data buffer, UxRXBUF, contains the character moved from the RX shift register after the character is received.

Figure 13−5. State Diagram of Receiver Enable

No Valid Start Bit

URXEx = 0			Not Completed
URXEx = 1		URXEx = 1
	Idle State	Valid Start Bit	Receiver
Receive				Handle Interrupt
	(Receiver		Collects
Disable				Conditions
	Enabled)		Character
URXEx = 0
				Character
		URXEx = 1		Received

URXEx = 0

Note: Re-Enabling the Receiver (Setting URXEx): UART Mode

When the receiver is disabled (URXEx = 0), re-enabling the receiver (URXEx

=1) is asynchronous to any data stream that may be present on URXDx at the time. Synchronization can be performed by testing for an idle line condition before receiving a valid character (see URXWIE).

USART Peripheral Interface, UART Mode 13-9