User manual

21 Chapter 3
3.3 Interrupt Functions
3.3.1 Introduction
Two lines of each I/O port C, plus ports A0 and B0, are connected to the
interrupt circuitry. The “Interrupt Control Register” of the PCI-1753/
1753E controls how the combination of these signals generates an
interrupt. Six interrupt request signals can be generated at the same time,
and then the software can service these six request signals by IRQ. The
multiple interrupt sources provide the card with more capability and
flexibility.
3.3.2 IRQ Level
The IRQ level is set automatically by the PCI plug-and-play BIOS and is
saved in the PCI controller. There is no need for users to set the IRQ
level. Only one IRQ level is used by this card, although it has six
interrupt sources.
3.3.3 Interrupt Control Registers
The “Interrupt Control Registers” (Base + 16, 17, 18 and 19 for the
PCI-1753, and Base + 48, 49, 50 and 51 for the PCI-1753E) control the
interrupt signal sources, edges and flags. The following table shows the
bit map of each interrupt control register. These registers are readable/
writable. When writing to one of them, it is used as a control register, and
when reading from it, it is used as a status register.