7BChapter Four: Operation
69BDeviceNet Messaging Protocol
49
The message body is a series of up to five, 8-bit fields that defines the specific explicit message.
The information included in the message body varies, depending on whether the message is a
request or a response.
The explicit message body consists of the following three required and two optional components:
Required:
•
Service
Code
(request and response)
(consists of Request/Response bit and Service ID)
•
Class Code
(request only)
•
Instance ID
(request only)
Optional:
•
Attribute
ID
(request only)
•
Service or Attribute Data
(request and response)
Note
In each message string, the CAN Data Field is represented by a series of
hexadecimal values.
Table 18: CAN Data Field
Byte
7
6
5 4 3 2 1 0
0
MESSAGE
HEADER
Fragment Bit
(0/1)
Transaction
ID (XID) Bit
(0/1)
Node Address
6-bit Hexadecimal Value
1
MESSAGE
BODY
Service Code
Calculate the combined hexadecimal value of the request/response bit (bit 7) and the
assigned Service ID hex value (bits 6 to 0)
Request Bit
(0) or
Response Bit
(1)
Service ID
Assigned hexadecimal value
2 Class
Code
Assigned hexadecimal value
3 Instance
ID
Assigned hexadecimal value
Fragment Bit
This 1-bit field indicates whether the message is complete or fragmented. A message must be
fragmented if it is larger than 8 bytes. Refer to the ODVA “DeviceNet Specification,” Volume I
[1] for more information.
The fragment bit values are:
0 = Non-fragmented
1 = Fragmented
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