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Appendix A
Explicit Messages
DeviceNet explicit messages sent from the Master Unit to a GRT1-series DeviceNet Communications Unit can
be used to read or write any parameter of a specified GRT1-series DeviceNet Communications Unit.
The DeviceNet Communications Units process the commands sent from the Master and then return
responses.
Basic Format of Explicit Messages
The basic format of each command and response is shown below.
Command Block
Destination Node Address
The node address of the Unit that is sending the explicit messages (commands) is specified as a single-byte
hexadecimal.
Service Code, Class ID, Instance ID, Attribute ID
The parameters used for specifying the command, processing object, and processing content.
Note The number of bytes designated for Class ID, Instance ID, and Attribute ID depend on the Master Unit.
When sent from an OMRON DeviceNet Master, the Class ID and Instance ID are 2 bytes (4 digits), and
Attribute ID is 1 byte (2 digits).
Class ID
If the class ID is 0 × 80 to 0 × 90, a message is being sent to a Slice I/O Unit via the Communications Unit.
Instance ID
This parameter gives the unit number of the Slice I/O Unit (1 to 63).
Data
Data is not required when the read command is used.
Response Block
Normal Response Block
Error Response Block
Number of Bytes Received
The number of bytes received from the source node address is returned in hexadecimal. When an error
response is returned for an explicit message, the number of bytes is always 0004 hex.
Destination
node address
Service
code
Class
ID
Instance
ID
Attribute
ID
Data
Number of bytes
received
Source node
address
Service code Data
Number of bytes
received:
0004 hex (fixed)
Source node
address
Service code Error code
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