TL16CP754C datasheet(13/49 Pages) TI

13 / 49 page

TL16CP754C, TL16CM754C, TL16C754C

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SLLS644E – DECEMBER 2007 – REVISED MAY 2010

Table 4. Interrupt Control Functions

PRIORITY

INTERRUPT

IIR[5–0]

INTERRUPT SOURCE

INTERRUPT RESET METHOD

LEVEL

TYPE

000001

None

000110

Receiver line

OE, FE, PE, or BI errors occur in

FE < PE < BI: All erroneous characters are

status

characters in the RX FIFO

read from the RX FIFO. OE: Read LSR

001100

RX timeout

Stale data in RX FIFO

Read RHR

000100

RHR interrupt

DRDY (data ready)

Read RHR

(FIFO disable)

RX FIFO above trigger level (FIFO enable)

000010

THR interrupt

TFE (THR empty)

Read IIR OR a write to the THR

(FIFO disable)

TX FIFO passes above trigger level (FIFO

enable)

000000

Modem status

MSR[3:0]= 0

Read MSR

010000

Xoff interrupt

Receive Xoff character(s)/special character Receive Xon character(s)/Read of IIR

100000

CTS, RTS

RTS pin or CTS pin change state from

Read IIR

active (low) to inactive (high)

It is important to note that for the framing error, parity error, and break conditions, LSR[7] generates the interrupt.

LSR[7] is set when there is an error anywhere in the RX FIFO and is cleared only when there are no more errors

remaining in the FIFO. LSR[4–2] always represent the error status for the received character at the top of the Rx

FIFO. Reading the Rx FIFO updates LSR[4–2] to the appropriate status for the new character at the top of the

FIFO. If the Rx FIFO is empty, then LSR[4–2] is all zeros.

For the Xoff interrupt, if an Xoff flow character detection caused the interrupt, the interrupt is cleared by an Xon

flow character detection. If a special character detection caused the interrupt, the interrupt is cleared by a read of

the ISR.

Interrupt Mode Operation

In interrupt mode (if any bit of IER[3:0] is1), the processor is informed of the status of the receiver and transmitter

by an interrupt signal, INT. Therefore, it is not necessary to continuously poll the line status register (LSR) to see

if any interrupt needs to be serviced. Figure 5 shows interrupt mode operation.

Figure 5. Interrupt Mode Operation

Polled Mode Operation

In polled mode (IER[3:0] = 0000), the status of the receiver and transmitter can then be checked by polling the

line status register (LSR). This mode is an alternative to the interrupt mode of operation where the status of the

receiver and transmitter is automatically known by means of interrupts sent to the CPU. Figure 6 shows polled

mode operation.

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