National Instruments NI-DNET - Manual (Page 32)

© National Instruments Corporation 4-1 NI-DNET User Manual
4
NI-DNET Programming
Techniques
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.
Configuring I/O Connections
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,
NI-DNET Software Overview .
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.
Expected Packet Rate
Each DeviceNet I/O connection contains an attribute called the expected
packet rate, which specifies the expected rate (in milliseconds) of messages
(
packets ) 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.