Datasheet

Interrupt Enable Register (IER)
Interrupt Identification Register (IIR)
TL16C550D , , TL16C550DI
www.ti.com .................................................................................................................................................. SLLS597E – APRIL 2004 – REVISED DECEMBER 2008
• LSR6 indicates that both the THR and TSR are empty. LSR7 indicates whether any errors are in the receiver
FIFO.
There is no trigger level reached or time-out condition indicated in the FIFO-polled mode. However, the receiver
and transmitter FIFOs are still fully capable of holding characters.
The IER enables each of the five types of interrupts (see Table 5 ) and enables INTRPT in response to an
interrupt generation. The IER can also disable the interrupt system by clearing bits 0 through 3. The contents of
this register are summarized in Table 3 and are described in the following bullets.
• Bit 0: When set, this bit enables the received data available interrupt.
• Bit 1: When set, this bit enables the THRE interrupt.
• Bit 2: When set, this bit enables the receiver line status interrupt.
• Bit 3: When set, this bit enables the modem status interrupt.
• Bits 4 through 7: These bits are not used (always cleared).
The ACE has an on-chip interrupt generation and prioritization capability that permits a flexible interface with the
most popular microprocessors.
The ACE provides four prioritized levels of interrupts:
• Priority 1 − Receiver line status (highest priority)
• Priority 2 − Receiver data ready or receiver character time-out
• Priority 3 − Transmitter holding register empty
• Priority 4 − Modem status (lowest priority)
When an interrupt is generated, the IIR indicates that an interrupt is pending and encodes 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 5 . Detail on each bit is as follows:
• Bit 0: This bit is used either in a hardwire-prioritized or polled-interrupt system. When bit 0 is cleared, an
interrupt is pending. If bit 0 is set, no interrupt is pending.
• Bits 1 and 2: These two bits identify the highest priority interrupt pending as indicated in Table 3 .
• Bit 3: This bit is always cleared in TL16C450 mode. In FIFO mode, bit 3 is set with bit 2 to indicate that a
time-out interrupt is pending.
• Bits 4 and 5: These two bits are not used (always cleared).
• Bits 6 and 7: These bits are always cleared in TL16C450 mode. They are set when bit 0 of the FIFO control
register is set.
Table 5. Interrupt Control Functions
INTERRUPT IDENTIFICATION
PRIORITY INTERRUPT RESET
REGISTER
INTERRUPT TYPE INTERRUPT SOURCE
LEVEL METHOD
BIT 3 BIT 2 BIT 1 BIT 0
0 0 0 1 None None None None
Overrun error, parity error,
0 1 1 0 1 Receiver line status framing error, or break Read the line status register
interrupt
Receiver data available in the
Received data TL16C450 mode or trigger Read the receiver buffer
0 1 0 0 2
available level reached in the FIFO register
mode
No characters have been
removed from or input to the
Character time-out receiver FIFO during the last Read the receiver buffer
1 1 0 0 2
indication four character times, and there register
is at least one character in it
during this time
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