LM3S308 Luminary Micro, Inc, LM3S308 Datasheet - Page 260

• Manufacturer Part Number: LM3S308
• Description: Lm3s308 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Universal Asynchronous Receivers/Transmitters (UARTs)
12.2.6
12.3
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All of the interrupt events are ORed together before being sent to the interrupt controller, so the
UART can only generate a single interrupt request to the controller at any given time. Software can
service multiple interrupt events in a single interrupt service routine by reading the UART Masked
Interrupt Status (UARTMIS) register (see page 280).
The interrupt events that can trigger a controller-level interrupt are defined in the UART Interrupt
Mask (UARTIM ) register (see page 277) by setting the corresponding IM bit to 1. If interrupts are
not used, the raw interrupt status is always visible via the UART Raw Interrupt Status (UARTRIS)
register (see page 279).
Interrupts are always cleared (for both the UARTMIS and UARTRIS registers) by setting the
corresponding bit in the UART Interrupt Clear (UARTICR) register (see page 281).
The receive timeout interrupt is asserted when the receive FIFO is not empty, and no further data
is received over a 32-bit period. The receive timeout interrupt is cleared either when the FIFO
becomes empty through reading all the data (or by reading the holding register), or when a 1 is
written to the corresponding bit in the UARTICR register.
Loopback Operation
The UART can be placed into an internal loopback mode for diagnostic or debug work. This is
accomplished by setting the LBE bit in the UARTCTL register (see page 273). In loopback mode,
data transmitted on UnTx is received on the UnRx input.
Initialization and Configuration
To use the UARTs, the peripheral clock must be enabled by setting the UART0 or UART1 bits in the
RCGC1 register.
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:
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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 258, 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 269) should be set to 10.
The value to be loaded into the UARTFBRD register (see page 270) is calculated by the equation:
Transmit (when condition defined in the TXIFLSEL bit in the UARTIFLS register is met)
Receive (when condition defined in the RXIFLSEL bit in the UARTIFLS register is met)
115200 baud rate
Data length of 8 bits
One stop bit
No parity
FIFOs disabled
No interrupts
Preliminary
June 04, 2008