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Issue
98, September 1998
Networking
with DeviceNet
by
Jim Brady
Start
• Sorting Them Out
• New
Breed •
Motivation •
Can •
Message Reliability •
DeviceNet Connections •
Device Net Messages •
Stringing Messages Together •
Some Real Messages •
Object Library •
Conformance Testing •
DeviceNet Standards •
References,Sources,PDF
Object
Library
With
DeviceNet, a device is modeled as a collection of objects.
Each object has attributes and behaviors, and can be implemented
directly as a C++ class. Figure 5 shows the object model
for a DeviceNet device with two analog sensors.
Each
class has a class ID, objects have an instance ID, and
attributes have an attribute ID. By specifying these three
ID numbers, any attribute in the device can be addressed.
The
DeviceNet Object Library is contained in Volume II of
the standard. In addition to network-related objects,
it includes about 25 objects that model real-world switches,
sensors, actuators, PID loops, position sensors, and controllers.
There are more on the way, including an Analog Sensor
Object that models advanced sensors, with capabilities
such as calibration, auto-zero, offset, gain, and setpoints.
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