National Instruments PC-DIO-96/PnP, User Manual

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Chapter 4 Theory of Operation
PC-DIO-96/PnP User Manual 4-2 © National Instruments Corporation
The PC I/O channel consists of an address bus, a data bus, interrupt
lines, and several control and support signals.
Data Transceivers
The data transceivers control the sending and receiving of data to and
from the PC I/O channel.
PC I/O Channel Control Circuitry
The I/O channel control circuitry monitors and transmits the PC
I/O channel control and support signals. The control signals identify
transfers as read or write, memory or I/O, and 8-bit, 16-bit, or 32-bit
transfers. The PC-DIO-96PnP uses only 8-bit transfers.
Plug and Play Circuitry
The board’s Plug and Play circuitry automatically arbitrates and assigns
system resources. All bus-related configuration, such as setting the
board’s base address and interrupt level, is performed through software.
Interrupt Control Circuitry
The interrupt channel used by the PC-DIO-96PnP is selected by the
Plug and Play circuitry. Two software-controlled registers determine
which devices, if any, generate interrupts. Each of the four 82C55A
devices has two interrupt lines, PC3 and PC0, connected to the interrupt
circuitry.