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Theory of Operation Chapter 5
PC-OPDIO-16 User Manual 5-2 © National Instruments Corporation
You can execute data acquisition functions by using the digital I/O circuitry. The internal data
and control buses interconnect the components. Optical isolation is attained by the optical
isolation circuitry.
Theory of Operation
I/O Channel Interface Circuitry
The PC I/O channel of the PC-OPDIO-16 consists of an address bus, a data bus, a Plug and Play
interface, and several control and support signals. The components making up the PC I/O
channel interface circuitry are shown in Figure 5-2.
PC I/O Channel
Address Bus
Data
Buffers
Timing
Interface
Plug and Play/
Address Decoder
Control Lines
Data Bus
Register Selects
Internal Data Bus
Control and
Read/Write Signals
Figure 5-2. PC I/O Interface Circuitry Block Diagram of PC-OPDIO-16
The circuitry consists of Plug and Play, address decoder, data buffers, and I/O channel interface
timing control circuitry. The circuitry monitors the address lines to generate the board enable
signal. The data buffers control the direction of data transfer on the bidirectional data lines based
on whether the transfer is a read or write.
Digital I/O Circuitry
The PC-OPDIO-16 supports 8-bit digital input and 8-bit digital output. The 16 bits are
configured as two 8-bit ports, one for input and the other for output. The digital I/O circuitry is