TL16C554FN datasheet(19/33 Pages) TI

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TL16C554, TL16C554I

ASYNCHRONOUS COMMUNICATIONS ELEMENT

SLLS165D – JANUARY 1994 – REVISED JULY 1998

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

interrupt enable register (IER) (continued)

D Bit 0: When IER0 is set, IER0 enables the received data available interrupt and the timeout interrupts in

the FIFO mode.

D Bit 1: When IER1 is set, the transmitter holding register empty interrupt is enabled.

D Bit 2: When IER2 is set, the receiver line status interrupt is enabled.

D Bit 3: When IER3 is set, the modem status interrupt is enabled.

D Bits 4 – 7: IER4 – IER7. These four bits of the IER are cleared.

interrupt identification register (IIR)

In order to minimize software overhead during data character transfers, the serial channel prioritizes interrupts

into four levels. The four levels of interrupt conditions are as follows:

D Priority 1 – Receiver line status (highest priority)

D Priority 2 – Receiver data ready or receiver character timeout

D Priority 3 –Transmitter holding register empty

D Priority 4–Modem status (lowest priority)

Information indicating that a prioritized interrupt is pending and the type of interrupt that is stored in the IIR. The

IIR indicates the highest priority interrupt pending. The contents of the IIR are indicated in Table 5.

Table 5. Interrupt Control Functions

INTERRUPT

IDENTIFICATION

INTERRUPT SET AND RESET FUNCTIONS

BIT 3

BIT 2

BIT 1

BIT 0

PRIORITY

LEVEL

INTERRUPT TYPE

INTERRUPT SOURCE

INTERRUPT

RESET CONTROL

—

None

—

First

Receiver line status

OE, PE, FE, or BI

LSR read

Second

Received data available

Receiver data available or

trigger level reached

RBR read until FIFO

drops below the trigger

level

Second

Character time-out

indicator

No characters have been

removed from or input to the

receiver FIFO during the last

four character times, and there

is at least one character in it

during this time.

RBR read

Third

THRE

IIR read if THRE is the

interrupt source or THR

write

Fourth

Modem status

CTS, DSR, RI, or DCD

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