LM3S1636_13 Datasheet, PDF (430/655 Pages) Texas Instruments – Stellaris Microcontroller

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Universal Asynchronous Receivers/Transmitters (UARTs)
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 425, 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 439) should be set to 10.
The value to be loaded into the UARTFBRD register (see page 440) 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 12-2 on page 430 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
■ UART2: 0x4000.E000
Note that the UART module clock must be enabled before the registers can be programmed (see
page 214). 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 443)
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 12-2. UART Register Map
Offset Name
Type
0x000 UARTDR
R/W
0x004 UARTRSR/UARTECR R/W
0x018 UARTFR
RO
0x020 UARTILPR
R/W
0x024 UARTIBRD
R/W
0x028 UARTFBRD
R/W
Reset
0x0000.0000
0x0000.0000
0x0000.0090
0x0000.0000
0x0000.0000
0x0000.0000
Description
UART Data
UART Receive Status/Error Clear
UART Flag
UART IrDA Low-Power Register
UART Integer Baud-Rate Divisor
UART Fractional Baud-Rate Divisor
See
page
432
434
436
438
439
440
430
July 24, 2012
Texas Instruments-Production Data