LM3S101 Datasheet, PDF (306/445 Pages) List of Unclassifed Manufacturers – Microcontroller

Universal Asynchronous Receivers/Transmitters (UARTs)
10.3.6
10.4
the FIFO must be written past the programmed trigger level otherwise no further transmit interrupts
will be generated. The transmit interrupt is cleared by writing data to the transmit FIFO until it
becomes greater than the trigger level, or by clearing the interrupt by writing a 1 to the TXIC bit.
■ If the FIFOs are disabled (have a depth of one location) and there is no data present in the
transmitters single location, the TXRIS bit is set. It is cleared by performing a single write to the
transmit FIFO, or by clearing the interrupt by writing a 1 to the TXIC bit.
Loopback Operation
The UART can be placed into an internal loopback mode for diagnostic or debug work. This is
accomplished by setting the LBE bit in the UARTCTL register (see page 319). In loopback mode,
data transmitted on UnTx is received on the UnRx input.
Initialization and Configuration
To use the UART, the peripheral clock must be enabled by setting the UART0 bit in the RCGC1
register.
This section discusses the steps that are required to use a UART module. For this example, the
UART clock is assumed to be 20 MHz and the desired UART configuration is:
■ 115200 baud rate
■ Data length of 8 bits
■ One stop bit
■ No parity
■ FIFOs disabled
■ No interrupts
The first thing to consider when programming the UART is the baud-rate divisor (BRD), since the
UARTIBRD and UARTFBRD registers must be written before the UARTLCRH register. Using the
equation described in “Baud-Rate Generation” on page 303, the BRD can be calculated:
BRD = 20,000,000 / (16 * 115,200) = 10.8507
which means that the DIVINT field of the UARTIBRD register (see page 315) should be set to 10.
The value to be loaded into the UARTFBRD register (see page 316) is calculated by the equation:
UARTFBRD[DIVFRAC] = integer(0.8507 * 64 + 0.5) = 54
With the BRD values in hand, the UART configuration is written to the module in the following order:
1. Disable the UART by clearing the UARTEN bit in the UARTCTL register.
2. Write the integer portion of the BRD to the UARTIBRD register.
3. Write the fractional portion of the BRD to the UARTFBRD register.
4. Write the desired serial parameters to the UARTLCRH register (in this case, a value of
0x0000.0060).
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July 14, 2014
Texas Instruments-Production Data