UART/Autobaud Functional Description
12-40
Table 12–42. Generic Interrupt Descriptions in Modem Mode (Continued)
IIR[5 - 0]
Interrupt Reset Method
Interrupt Source
Interrupt
Type
Priority
Level
0 1 0 0 0 0
5
XOFF
interrupt/special
character
interrupt
Receive XOFF characters(s)/
special character
Receive XON character(s), if
XOFF interrupt/read of IIR, if
special character interrupt
1 0 0 0 0 0
6
CTS, RTS,
DSR
RTS pin, CTS pin or DSR pin
change state from active (low)
to inactive (high).
Read IIR
Note:
Once LSR[7] (RX_FIFO_STS) is set to FIFO disable (FCR[0]=0), this bit bit cannot be cleared by reading LSR. First,
FCR[1] (RX_FIFO_CLERA) must be set to 1, then LSR[7] can be cleared.
LSR[7] generates the receiver line status interrupt.
For the XOFF interrupt, if an XOFF flow character detection caused the inter-
rupt, the interrupt is cleared by an XON flow character detection. If special
character detection caused the interrupt, the interrupt is cleared by a read of
the interrupt identification register (IIR).
12.5.3.2 Wake-Up Interrupt
The wake-up interrupt is uniquely designed and is enabled when SCR[4] is set
to 1. The interrupt identification register (IIR) is not modified when this interrupt
occurs; SSR[1] must be checked to detect a wake-up event. When wake-up
interrupt occurs, the only way to clear it is to reset SCR[4] to 0.
12.5.3.3 FIFO Interrupt Mode
In FIFO interrupt mode, FCR[0] = 1 and relevant interrupts are enabled via the
interrupt enable register (IER). The processor is informed of the status of the
receiver and transmitter by an interrupt signal, nIRQ. These interrupts are
raised when receive/transmit FIFO threshold (respectively TLR[7:4] and
TLR[3:0] or FCR[7:6] and FCR[5:4]) are reached; they instruct the host (MPU
or DSP) to transfer data to the destination (from UART module in receive mode
and from any source to UART FIFO in transmit mode).
When UART flow control is enabled along with interrupt capabilities, you must
ensure that the UART flow control FIFO threshold (TCR[3:0]) is greater than
or equal to the receive FIFO threshold.
Figure 12–9 shows receive IT operations; Figure 12–10 shows transmit IT
operations.