ProSoft Technology CompactLogix MVI69E-MBS User Manual page 122

MVI69E-MBS ♦ CompactLogix™ Platform
Modbus Serial Enhanced Communication Module
A server device can, however, be forced into 'Listen Only Mode' in which it monitors the
messages on the communications system but not respond to them. This can affect the
outcome of your application program if it depends upon any further exchange of data
with the remote device. Generally, the mode is forced to remove a malfunctioning
remote device from the communications system.
Sub-function Codes Supported
Only Sub-function 00 is supported by the MVI69E-MBS module.
00 Return Query Data
The data passed in the request data field is to be returned (looped back) in the
response. The entire response message should be identical to the request.
Sub-function
00 00
Example and State Diagram
Here is an example of a request to remote device to Return Query Data. This uses a
sub-function code of zero (00 00 hex in the two-byte field). The data to be returned is
sent in the two-byte data field (A5 37 hex).
Request
Field Name
Function
Sub-function Hi
Sub-function Lo
Data Hi
Data Lo
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Data Field (Request)
Any
Response
(Hex) Field Name
08 Function
00 Sub-function Hi
00 Sub-function Lo
A5 Data Hi
37 Data Lo
Data Field (Response)
Echo Request Data
(Hex)
08
00
00
A5
27
Reference
User Manual
Page 122 of 159