LM3S9792 Datasheet, PDF (594/1279 Pages) Texas Instruments – Stellaris® LM3S9792 Microcontroller

Universal Asynchronous Receivers/Transmitters (UARTs)
■ Overrun Error
■ Break Error
■ Parity Error
■ Framing Error
■ Receive Timeout
■ Transmit (when condition defined in the TXIFLSEL bit in the UARTIFLS register is met, or if the
EOT bit in UARTCTRL is set, when the last bit of all transmitted data leaves the serializer)
■ Receive (when condition defined in the RXIFLSEL bit in the UARTIFLS register is met)
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 625).
The interrupt events that can trigger a controller-level interrupt are defined in the UART Interrupt
Mask (UARTIM) register (see page 617) by setting the corresponding IM bits. If interrupts are not
used, the raw interrupt status is always visible via the UART Raw Interrupt Status (UARTRIS)
register (see page 621).
Interrupts are always cleared (for both the UARTMIS and UARTRIS registers) by writing a 1 to the
corresponding bit in the UART Interrupt Clear (UARTICR) register (see page 628).
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.
14.3.10
Loopback Operation
The UART can be placed into an internal loopback mode for diagnostic or debug work by setting
the LBE bit in the UARTCTL register (see page 611). In loopback mode, data transmitted on the
UnTx output is received on the UnRx input.
14.3.11
DMA Operation
The UART provides an interface to the μDMA controller with separate channels for transmit and
receive. The DMA operation of the UART is enabled through the UART DMA Control
(UARTDMACTL) register. When DMA operation is enabled, the UART asserts a DMA request on
the receive or transmit channel when the associated FIFO can transfer data. For the receive channel,
a single transfer request is asserted whenever any data is in the receive FIFO. A burst transfer
request is asserted whenever the amount of data in the receive FIFO is at or above the FIFO trigger
level configured in the UARTIFLS register. For the transmit channel, a single transfer request is
asserted whenever there is at least one empty location in the transmit FIFO. The burst request is
asserted whenever the transmit FIFO contains fewer characters than the FIFO trigger level. The
single and burst DMA transfer requests are handled automatically by the μDMA controller depending
on how the DMA channel is configured.
To enable DMA operation for the receive channel, set the RXDMAE bit of the DMA Control
(UARTDMACTL) register. To enable DMA operation for the transmit channel, set the TXDMAE bit
of the UARTDMACTL register. The UART can also be configured to stop using DMA for the receive
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June 14, 2010
Texas Instruments-Advance Information