LM3S9B81_15 Datasheet, PDF (679/1271 Pages) Texas Instruments – Stellaris LM3S9B81 Microcontroller

Stellaris^® LM3S9B81 Microcontroller
13.3.9
if the ¼ option is selected for the receive FIFO, the UART generates a receive interrupt after 4 data
bytes are received. Out of reset, both FIFOs are configured to trigger an interrupt at the ½ mark.
Interrupts
The UART can generate interrupts when the following conditions are observed:
■ 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 UARTCTL 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 711).
The interrupt events that can trigger a controller-level interrupt are defined in the UART Interrupt
Mask (UARTIM) register (see page 703) 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 707).
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 715).
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.
The receive interrupt changes state when one of the following events occurs:
■ If the FIFOs are enabled and the receive FIFO reaches the programmed trigger level, the RXRIS
bit is set. The receive interrupt is cleared by reading data from the receive FIFO until it becomes
less than the trigger level, or by clearing the interrupt by writing a 1 to the RXIC bit.
■ If the FIFOs are disabled (have a depth of one location) and data is received thereby filling the
location, the RXRIS bit is set. The receive interrupt is cleared by performing a single read of the
receive FIFO, or by clearing the interrupt by writing a 1 to the RXIC bit.
The transmit interrupt changes state when one of the following events occurs:
■ If the FIFOs are enabled and the transmit FIFO progresses through the programmed trigger
level, the TXRIS bit is set. The transmit interrupt is based on a transition through level, therefore
the FIFO must be written past the programmed trigger level otherwise no further transmit interrupts
will be generated. The transmit interrupt is cleared by writing data to the transmit FIFO until it
becomes greater than the trigger level, or by clearing the interrupt by writing a 1 to the TXIC bit.
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