Quatech ES-100 Figure 16 --- Interrupt Identification Register bit decoding

IP --- Interrupt pending:
When logic 0, indicates that an interrupt is pending and the contents of the interrupt
identification register may be used to determine the interrupt source. See Figure 16.
0
IID0 ---
1
IID1 ---
2
Interrupt Identification:
Indicates highest priority interrupt pending if any. See Figure 16.
NOTE: IID2 is always a logic 0 on the 16450 or in non-FIFO mode on the 16550.
IID2 ---
3
0 --- reserved4
0 --- reserved5
FFE --- FIFO enable: (16550 only)
When logic 1, indicates FIFO mode enabled. Always logic 0 for the 16450.
6
FFE --- FIFO enable: (16550 only)
When logic 1, indicates FIFO mode enabled. Always logic 0 for the 16450.
7
DESCRIPTIONBIT
Figure 15 --- Interrupt Identification Register bit definitions
Figure 16 gives the detail of the IIDx bits in the Interrupt Identification
Register. These bits are examined to determine the source of an interrupt.
MODEM Status: Indicates clear to send, data set ready, ring indicator, or
data carrier detect have changed state. The interrupt is cleared by reading the
MODEM status register.
4th0000
Transmitter Holding Register Empty: Indicates the transmitter holding
register is empty. The interrupt is cleared by reading the interrupt
identification register or writing to the transmitter holding register. (Indicates
transmit FIFO empty for 16550.)
3rd0100
Character Timeout (16550 FIFO mode only): Indicates no characters have
been removed from or input to the receiver FIFO for the last four character
times and there is data present in the receiver FIFO. The interrupt is cleared by
reading the receiver FIFO.
2nd0011
Received Data Ready (16450 or 16550): Indicates receive data available.
The interrupt is cleared by reading the receive buffer. In 16550 FIFO mode,
indicates the receiver FIFO trigger level has been reached. The interrupt is
reset when the FIFO drops below the trigger level.
2nd0010
Receiver Line Status: Indicates overrun, parity, framing errors or break
interrupts. The interrupt is cleared by reading the line status register.
1st0110
None
N/A1don't care
012
Interrupt TypePriorityIPIIDx bits
Figure 16 --- Interrupt Identification Register bit decoding
Quatech ES-100D User's Manual 15