Texas Instruments MSP430x1xx manual Usart Operation Uart Mode, Usart Initialization and Reset

USART Operation: UART Mode

13.2 USART Operation: UART Mode

In UART mode, the USART transmits and receives characters at a bit rate asynchronous to another device. Timing for each character is based on the selected baud rate of the USART. The transmit and receive functions use the same baud rate frequency.

13.2.1 USART Initialization and Reset

The USART is reset by a PUC or by setting the SWRST bit. After a PUC, the SWRST bit is automatically set, keeping the USART in a reset condition. When set, the SWRST bit resets the URXIEx, UTXIEx, URXIFGx, RXWAKE, TXWAKE, RXERR, BRK, PE, OE, and FE bits and sets the UTXIFGx and TXEPT bits. The receive and transmit enable flags, URXEx and UTXEx, are not altered by SWRST. Clearing SWRST releases the USART for operation. See also chapter USART Module, I2C mode for USART0 when reconfiguring from I2C mode to UART mode.

Note: Initializing or Re-Configuring the USART Module

The required USART initialization/re-configuration process is:

1)Set SWRST (BIS.B #SWRST,&UxCTL)

2)Initialize all USART registers with SWRST = 1 (including UxCTL)

3)Enable USART module via the MEx SFRs (URXEx and/or UTXEx)

4) Clear SWRST via software (BIC.B #SWRST,&UxCTL)

5)Enable interrupts (optional) via the IEx SFRs (URXIEx and/or UTXIEx) Failure to follow this process may result in unpredictable USART behavior.

13.2.2Character Format

The UART character format, shown in Figure 13−2, consists of a start bit, seven or eight data bits, an even/odd/no parity bit, an address bit (address-bit mode), and one or two stop bits. The bit period is defined by the selected clock source and setup of the baud rate registers.

Figure 13−2. Character Format

								Mark
	ST	D0	D6	D7	AD	PA	SP SP
								Space
								[2nd Stop Bit, SP = 1]
								[Parity Bit, PENA = 1]
[Optional Bit, Condition]								[Address Bit, MM = 1]
								[8th Data Bit, CHAR = 1]

13-4USART Peripheral Interface, UART Mode