LM3S1626 Datasheet, PDF (469/716 Pages) Texas Instruments – ARM and Thumb are registered trademarks and Cortex is a trademark

Stellaris® LM3S1626 Microcontroller
12.5
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 464, 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 478) should be set to 10.
The value to be loaded into the UARTFBRD register (see page 479) 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 260)
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 12-2 on page 470 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
■ UART1: 0x4000.D000
Note that the UART module clock must be enabled before the registers can be programmed (see
page 216). There must be a delay of 3 system clocks after the UART module clock is enabled before
any UART module registers are accessed.
November 17, 2011
469
Texas Instruments-Production Data