National Instruments PC-DIO-24 Chapter 3 Theory of Operation

© National Instruments Corporation 3-1 PC-DIO-24 User Manual
Chapter 3
Theory of Operation
This chapter contains a functional overview of the PC-DIO-24 board and explains the operation
of each functional unit making up the PC-DIO-24.
The block diagram in Figure 3-1 illustrates the key functional components of the PC-DIO-24
board.
I/O Connector
Interrupt
Control
Circuitry
82C55A
PPI
PC I/O
Channel
Control
Circuitry
Address
Decoder
Bus
Transceivers
PA
PB
PC
/
8
/
8
/
8
PC3
PC0
+5 V
PC I/O Channel
1 A Fuse
Figure 3-1. PC-DIO-24 Block Diagram
The PC I/O Channel consists of an address bus, a data bus, interrupt lines, and several control
and support signals. Control and data transfers to the system microprocessor are asynchronous.