TL16C451FN datasheet(17/24 Pages) TI

17 / 24 page

TL16C451, TL16C452

ASYNCHRONOUS COMMUNICATIONS ELEMENTS

SLLS053C – MAY 1989 – REVISED AUGUST 1999

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

interrupt identification register (IIR)

The ACE has an on-chip interrupt generation and prioritization capability that permits a flexible interface with

most microprocessors.

The ACE provides four prioritized levels of interrupts:

D Priority 1 – Receiver line status (highest priority)

D Priority 2 – Receiver data ready or receiver character time out

D Priority 3 –Transmitter holding register empty

D Priority 4–Modem status (lowest priority)

When an interrupt is generated, the IIR indicates that an interrupt is pending and indicates the type of interrupt

in its three least significant bits (bits 0, 1, and 2). The contents of this register are summarized in Table 3 and

described in Table 4.

D Bit 0: This bit can be used either in a hardwire prioritized or polled interrupt system. When this bit is cleared,

an interrupt is pending. When bit 0 is set, no interrupt is pending.

D Bits 1 and 2: These two bits identify the highest priority interrupt pending as indicated in Table 4.

D Bits 3 – 7: These bits in the interrupt identification register are not used and are always clear.

Table 4. Interrupt Control Functions

INTERRUPT

IDENTIFICATION

PRIORITY

INTERRUPT TYPE

INTERRUPT SOURCE

INTERRUPT RESET

LEVEL

INTERRUPT TYPE

INTERRUPT SOURCE

METHOD

BIT 2

BIT 1

BIT 0

None

–

Overrun error, parity error,

Reading the line status

Receiver line status

framing error or break

Reading the line status

interrupt

Received data available

Receiver data available

Reading the receiver buffer

Received data available

Receiver data available

Reading the interrupt

Transmitter holding register

Identification register (if

Transmitter holding register

empty

Transmitter holding register

empty

source of interrupt) or writing

empty

into the transmitter holding

Clear to send, data set

Reading the modem status

Modem status

ready, ring indicator, or data

Reading the modem status

carrier detect

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