Basic Format Of Explicit Messages - Rockwell Automation Allen-Bradley Guard I/O DeviceNet 1732DS-IB8 User Manual

Basic Format of Explicit
Messages
The basic format of each command and response is as follows.
Table 26 - Command Block
Destination Node Address Service Code
· Destination Node Address - The node address of the module that is
sending the explicit messages is specified with a 1 byte hexadecimal.
· Service Code, Class ID, Instance ID, Attribute ID - The parameters used
for specifying the command, processing object, and processing content.
· Data - Data is not required when the read command is used.
Table 27 - Normal Response Block
Number of Bytes Received
Table 28 - Error Response Block
Number of Bytes Received 0004 hex (fixed)
· 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.
· Source Node Address - The node address of the node from which the
command was sent is returned in hexadecimal.
· Service Code - For normal completions, the service code specified in the
command with the leftmost bit turned ON is stored as shown in the
See Function, Command Service Code, and Response Service Code on
page 157.
Table 29 - Function, Command Service Code, and Response Service Code
Function Command Service Code (hex)
Read Data 10
Write Data 0E
Reset 05
Save 16
When an error response is returned for an explicit message, the value is always 94
hex.
· Data - Read data is included only when a read command is executed.
· Error code - The explicit message error code
Rockwell Automation Publication 1791DS-UM001J-EN-P - May 2013
Get Point Status from Modules by Using Explicit Messaging
Class ID Instance ID
Source Node Address Service Code
Source Node Address Service Code
Response Service Code (hex)
90
8E
85
96
Appendix A
Attribute ID Data
Data
Error Code
157