©
National Instruments Corporation
3-1
DAQCard-DIO-24 User Manual
Chapter
3
Hardware Overview
This chapter contains a functional overview of the DAQCard-DIO-24
and explains the operation of each functional unit making up the card.
Functional Overview
The block diagram in Figure 3-1 illustrates the key functional
components of the DAQCard-DIO-24.
Figure 3-1.
DAQCard-DIO-24 Block Diagram
.
82C55A Programmable Peripheral Interface
The 82C55A PPI is the heart of the DAQCard-DIO-24. This chip
has 24 programmable I/O pins that represent three 8-bit ports—port A,
port B, and port C. The chip also has three modes of operation: simple
I/O (mode 0), strobed I/O (mode 1), and bidirectional bus I/O (mode 2).
In mode 0, you can program port A, port B, and the upper and lower
four-bit nibbles of port C as input or output lines. In modes 1 and 2,
I/O Connector
82C55A
PPI
PA
PB
PC
/
8
/
8
/
8
/
8
PC3 (IRQ)
PC0 (IRQ)
PC Card I/O Channel
PC Card
I/O Channel
Interface
Circuitry
Data Bus
Control Lines
IRQ
Address
Bus
/
8
/
8
/
2
Data Bus
Control Lines
