Texas Instruments MSP430x1xx Asynchronous Communication Formats, Idle-Line Multiprocessor Format

USART Operation: UART Mode

13.2.3 Asynchronous Communication Formats

When two devices communicate asynchronously, the idle-line format is used for the protocol. When three or more devices communicate, the USART supports the idle-line and address-bit multiprocessor communication formats.

Idle-Line Multiprocessor Format

When MM = 0, the idle-line multiprocessor format is selected. Blocks of data are separated by an idle time on the transmit or receive lines as shown in Figure 13−3. An idle receive line is detected when 10 or more continuous ones (marks) are received after the first stop bit of a character. When two stop bits are used for the idle line the second stop bit is counted as the first mark bit of the idle period.

The first character received after an idle period is an address character. The RXWAKE bit is used as an address tag for each block of characters. In the idle-line multiprocessor format, this bit is set when a received character is an address and is transferred to UxRXBUF.

Figure 13−3. Idle -Line Format

UTXDx/URXDx

UTXDx/URXDx

Blocks of

Characters

Idle Periods of 10 Bits or More

UTXDx/URXDx Expanded

ST	Address	SP	ST	Data		SP	ST	Data	SP
First Character Within Block				Character Within Block			Character Within Block
Is Address. It Follows Idle
Period of 10 Bits or More					Idle Period Less Than 10 Bits

USART Peripheral Interface, UART Mode 13-5