TL16C554 Datasheet, PDF (19/33 Pages) Texas Instruments – ASYNCHRONOUS COMMUNICATIONS ELEMENT

TL16C554, TL16C554I
ASYNCHRONOUS COMMUNICATIONS ELEMENT
SLLS165D – JANUARY 1994 – REVISED JULY 1998
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
REGISTER
BIT 3 BIT 2 BIT 1 BIT 0
PRIORITY
LEVEL
INTERRUPT SET AND RESET FUNCTIONS
INTERRUPT TYPE
INTERRUPT SOURCE
INTERRUPT
RESET CONTROL
0
0
0
1
—
None
None
—
0
1
1
0
First Receiver line status
OE, PE, FE, or BI
LSR read
0
1
0
0
Second Received data available Receiver data available or
RBR read until FIFO
trigger level reached
drops below the trigger
level
1
1
0
0
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
0
0
1
0
Third THRE
THRE
IIR read if THRE is the
interrupt source or THR
write
0
0
0
0
Fourth Modem status
CTS, DSR, RI, or DCD
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