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Step 8 – Use DeviceNet Explicit Messaging
The control sequences in Step 7 showed how the network host computer can control the
inverter via polled I/O. While polled I/O data is continuously supplied (on each network
scan), it contains only a small set of control bits and values for the main running profile.
In addition, the inverter provides a direct way host computer to access individual inverter
parameters. In DeviceNet terminology, it is called explicit messaging.
The DeviceNet standards provide for a way to address individual devices on the network
(nodes), and data (attributes) within each device. A complete address consists of four
numbers: the Node Address (MAC ID), the Object Class Identifier, the Instance Number,
and the Attribute Number. An explicit message connection between two devices uses
these four numbers to identify and transfer data on a DeviceNet network. The four
address components and their ranges are shown in the following table:
Address
Component
Node
Class
Instance
Attribute
A particular inverter on the network has a specific node address (default = 63). To access
a particular parameter in that inverter, the host computer uses the class, instance, and
attribute numbers together. The address ranges indicated in the table above could access
any one of thousands of values within a device, if needed. In DeviceNet terminology, a
read access is called get, and a write access is called a set.
The assignment of DeviceNet explicit messaging addresses to inverters is somewhat
arbitrary. In this step we consider an example parameter, but the complete set for the
SJ100DN Series inverter is listed in the "Network Register Map" on page 78. The table
excerpt below shows parameter F_01 and its network address for explicit messaging.
"F" Group Parameters, Example
Func.
Name
Code
F_01 Output frequency setting
When you construct a get attribute or set attribute request, refer to the Class ID in the
table title bar (100), and the Inst, Attr, and Size columns (1, 159, 2).
Lowest
Highest
0
63
1
65535
0
65535
1
255
DeviceNet Class ID = 100
Inst Attr Size
1
159
SJ100DN Inverter
Range
Scaling
2
0 – 360Hz
61
Get/
Set
100
Get
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