LM3S2139 Luminary Micro, Inc, LM3S2139 Datasheet - Page 280

• Manufacturer Part Number: LM3S2139
• Description: Lm3s2139 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Universal Asynchronous Receivers/Transmitters (UARTs)
12.4
Table 12-1. UART Register Map
280
Offset
0x000
0x004
0x018
0x020
0x024
Name
UARTDR
UARTRSR/UARTECR
UARTFR
UARTILPR
UARTIBRD
■
■
■
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 276, 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 289) should be set to 10.
The value to be loaded into the UARTFBRD register (see page 290) 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.
2.
3.
4.
5.
Register Map
Table 12-1 on page 280 lists the UART registers. The offset listed is a hexadecimal increment to the
register’s address, relative to that UART’s base address:
■
■
Note:
No parity
FIFOs disabled
No interrupts
UART0: 0x4000.C000
UART1: 0x4000.D000
Disable the UART by clearing the UARTEN bit in the UARTCTL register.
Write the integer portion of the BRD to the UARTIBRD register.
Write the fractional portion of the BRD to the UARTFBRD register.
Write the desired serial parameters to the UARTLCRH register (in this case, a value of
0x0000.0060).
Enable the UART by setting the UARTEN bit in the UARTCTL register.
The UART must be disabled (see the UARTEN bit in the UARTCTL register on page 293)
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.
Type
R/W
R/W
R/W
R/W
RO
0x0000.0000
0x0000.0000
0x0000.0090
0x0000.0000
0x0000.0000
Reset
Preliminary
Description
UART Data
UART Receive Status/Error Clear
UART Flag
UART IrDA Low-Power Register
UART Integer Baud-Rate Divisor
July 25, 2008
page
See
282
284
286
288
289