AC37 High-Speed Communication Adapter Card
REGISTER DEFINITION
2-4
INTERRUPT IDENTIFICATION REGISTER:
OFFSET 2 - READ ONLY
This register can be read to determine if any interrupts are currently pending, and if so, what type. The AC37
prioritizes interrupts into the same four levels that the 16,550 UART does. The interrupt order of priority is:
1)
Receiver Line Status
2)
Receive Data Available
3)
Transmit Buffer Empty, and 4) Modem Status. The Interrupt ID Register bits are defined below:
Bit 0:
When this bit reads as a logic 0, an interrupt is pending and the contents of the Interrupt
ID Register can be used to vector to the appropriate interrupt service routine.
Bits 1–2:
These two bits are used to identify the highest priority interrupt pending. The four types
are identified per the table below.
Bits 3–7:
These bits are not used and will always read as logic 0.
A Line Status Interrupt is generated by either a receive buffer overrun or framing error. Refer to the Line Status
Register definition for a description of these errors. A Line Status Interrupt is cleared by reading the Line Status
Register.
A Receive Data Available Interrupt is generated whenever the Receive Data Available bit is set in the Line Status
Register. This interrupt is cleared by reading all data from the receive buffer or by resetting the FIFO. Refer to the
description of the Receive Data Available flag (bit 0) in the Line Status Register.
A Transmit Buffer Empty Interrupt is generated whenever the transmit FIFO is ready to receive data. Refer to the
description of the Transmit Buffer Empty flag (bit 5) in the Line Status Register.
A Modem Status Interrupt is generated by the Remote Bus IRQ line being active. Since the AC37 is not intended for
use with modems, the Remote Bus IRQ line is directed through what is normally the CTS bit on the 16,550 UART.
This interrupt is cleared by deactivating the Remote Bus IRQ line.
Bit 2
Bit 1
Bit 0
Priority
Interrupt Type
0
0
1
No Interrupt Pending
1
1
0
Highest
Line Status Interrupt
1
0
0
Second
Receive Data
Available
0
1
0
Third
Transmit Buffer Empty
0
0
0
Fourth
Modem Status
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