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This chapter describes various techniques to help you program your 
NI-DNET application. The techniques include configuration of 
I/O connection timing, using I/O data (assemblies), using explicit 
messaging, and handling multiple devices.

This section provides information on how I/O connections relate to one 
another and how your configuration of I/O connection timing can affect the 
overall performance of your DeviceNet system. The various types of 
I/O connections provided by DeviceNet are described in Chapter 1, 

In a master/slave DeviceNet I/O system, the master determines the timing 
of all I/O communication. Within your NI-DNET application, the 

ncOpenDnetIO

 function configures the timing for I/O connections in 

which your application communicates as master. As you read this section, 
you might want to refer to the description of the 

ncOpenDnetIO

 function 

in the NI-DNET Programmer Reference Manual.

Each DeviceNet I/O connection contains an attribute called the expected 
packet rate, which specifies the expected rate (in milliseconds) of messages 
(

) for the I/O connection. For NI-DNET, you use the 

ExpPacketRate

 parameter of the 

ncOpenDnetIO

 function to configure 

the expected packet rate.

After you start communication, the embedded microprocessor on your 
National Instruments DeviceNet interface transmits messages at the 

ExpPacketRate

. This means that after the I/O connection is configured, 

your NI-DNET application does not need to be concerned with the timing 
of messages on the DeviceNet network.