Datasheet

DocID024647 Rev 1 117/138
RM0352 UART (universal asynchronous receive transmit)
137
The transmit and receive data flow interrupts UARTRXINTR and UARTTXINTR have been
separated from the status interrupts. This enables use of the UARTRXINTR and
UARTTXINTR so that data can be read or written in response to the FIFO trigger levels.
The error interrupt, UARTEINTR, can be triggered when there is an error in the reception of
data. A number of error conditions are possible.
The modem status interrupt, UARTMSINTR, is a combined interrupt of all the individual
modem status signals.
The status of the individual interrupt sources can be read either from the raw interrupt status
register, UARTRIS -see Section 12.6.11 on page 131 or from the masked interrupt status
register, UARTMIS - see Section 12.6.12 on page 132.
12.4.1 UARTMSINTR
The modem status interrupt is asserted if any of the modem status signals (nUARTCTS,
nUARTDCD, nUARTDSR, and nUARTRI) change. It is cleared by writing a 1 to the
corresponding bit(s) in the interrupt clear register, UARTICR - see Section 12.6.13 on page
133, depending on the modem status signals that generated the interrupt.
12.4.2 UARTRXINTR
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.
When this happens, the receive interrupt is asserted HIGH. 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.
• If the FIFOs are disabled (have a depth of one location) and data is received thereby
filling the location, the receive interrupt is asserted HIGH. The receive interrupt is
cleared by performing a single read of the receive FIFO, or by clearing the interrupt.
12.4.3 UARTTXINTR
The transmit interrupt changes state when one of the following events occurs:
• If the FIFOs are enabled and the transmit FIFO is equal to or lower than the
programmed trigger level then the transmit interrupt is asserted HIGH. 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.
• If the FIFOs are disabled (have a depth of one location) and there is no data present in
the transmitters single location, the transmit interrupt is asserted HIGH. It is cleared by
performing a single write to the transmit FIFO, or by clearing the interrupt.