User manual

Chapter 3 Software Overview

Handshaking Versus No-Handshaking Digital I/O

Digital ports can output or input digital data in two ways. The first is to

immediately read or write data to or from the port. This type of digital I/O

is called no-handshaking mode. The second method is to coordinate digital

data transfers with another digital port. The second method is called digital

I/O with handshaking. With handshaking, you use dedicated transmission

lines to ensure that data on the receiving end is not overwritten with new

data before it is read from the input port.

NI-DAQ supports both handshaking and no-handshaking modes. The

application outlines within this section explain the use of both modes

where they apply.

Digital Port I/O Applications

Digital port I/O applications use individual digital ports to input or output

digital data. In addition, the applications input or output data points on

an individual basis.

You can configure individual port transfers for handshaking or

no-handshaking. All AT and PC devices with digital I/O ports can

use no-handshaking digital port I/O. DIO-24, 6025E devices,

AT-MIO-16DE-10, DIO-96, and Lab and 1200 devices can also

execute handshaking digital I/O for using the port I/O functions.

Figure 3-20 illustrates the series of calls for digital port I/O applications

with handshaking. Figure 3-21 illustrates the series of calls for digital port

I/O applications without handshaking.