69BDeviceNet Messaging Protocol 7BChapter Four: Operation
50
Transaction ID Bit
The transaction ID (XID) bit is a 1-bit field that is essentially a placeholder with a fixed value of
0.
Node Address
The node address is a 6-bit field that identifies the network address of the device as a
hexadecimal value. The source node address is the address of the device sending the m
essage.
The destination node address is the address of the device receiving the message.
In a request m
essage, the device address in the CAN Data Field is the source node address. In a
response message it is the destination node address.
Request/Response Bit
The request/response (R/R) bit (bit 7 in the service code) is a 1-bit field that specifies whether the
m
essage is a request or a response:
0 = Request
1 =
Response
Service ID
This 7-bit field (bits 6 to 0 in the service code) identifies the service being requested. The service
ID is a hexadecim
al value assigned by
ODVA.
Refer to Table 52, page 103, for a summary of the services supported by your device.
Class Code
The class code is a hexadecimal value, assigned by
ODVA, which identifies a specific Object
Model.
Instance ID
The instance ID is a hexadecim
al value, assigned by
ODVA, which identifies the instance within
an Object Model.
Service Data
The service data is the specific inform
ation required for a request, or reported in a response, in the
format assigned by
ODVA. The data may include an attribute ID, which is a hexadecimal value
assigned by ODVA, that identifies a specific parameter.
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