LM3S2276 Datasheet, PDF (496/785 Pages) Texas Instruments – Stellaris® LM3S2276 Microcontroller

Universal Asynchronous Receivers/Transmitters (UARTs)
13.5
■ 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 491, 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 505) should be set to 10.
The value to be loaded into the UARTFBRD register (see page 506) 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).
5. Optionally, configure the uDMA channel (see “Micro Direct Memory Access (μDMA)” on page 287)
and enable the DMA option(s) in the UARTDMACTL register.
6. Enable the UART by setting the UARTEN bit in the UARTCTL register.
Register Map
Table 13-2 on page 497 lists the UART registers. The offset listed is a hexadecimal increment to the
register’s address, relative to that UART’s base address:
■ UART0: 0x4000.C000
Note that the UART module clock must be enabled before the registers can be programmed (see
page 221). There must be a delay of 3 system clocks after the UART module clock is enabled before
any UART module registers are accessed.
Note: The UART must be disabled (see the UARTEN bit in the UARTCTL register on page 509)
before any of the control registers are reprogrammed. When the UART is disabled during
a TX or RX operation, the current transaction is completed prior to the UART stopping.
496
November 17, 2011
Texas Instruments-Production Data