LM3S1439_16 Datasheet, PDF (434/699 Pages) Texas Instruments – Stellaris LM3S1439 Microcontroller

Universal Asynchronous Receivers/Transmitters (UARTs)
■ 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 430, 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 443) should be set to 10.
The value to be loaded into the UARTFBRD register (see page 444) 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. Enable the UART by setting the UARTEN bit in the UARTCTL register.
12.5
Register Map
Table 12-3 on page 434 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 217). 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 447)
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.
Table 12-3. UART Register Map
Offset Name
Type
0x000 UARTDR
R/W
0x004 UARTRSR/UARTECR R/W
0x018 UARTFR
RO
Reset
0x0000.0000
0x0000.0000
0x0000.0090
Description
UART Data
UART Receive Status/Error Clear
UART Flag
See
page
436
438
440
434
July 15, 2014
Texas Instruments-Production Data