Sub-function codes supported, 00 return query data, Example and state diagram – ProSoft Technology 5201-MNET-ASCII User Manual
Page 63
MNET ♦ ProLinx Gateway
Modbus Protocol Specification
Modbus TCP/IP Interface Module
Driver Manual
ProSoft Technology, Inc.
Page 63 of 78
September 1, 2010
4.7.1 Sub-function codes supported
Only Sub-function 00 is supported by the MNET gateway.
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.
00 Return Query Data
Sub-function
Data Field (Request)
Data Field (Response)
00 00
Any
Echo Request Data
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).
Example and state diagram
Request
Response
Field Name
(Hex)
Field Name
(Hex)
Function
08
Function
08
Sub-function Hi
00
Sub-function Hi
00
Sub-function Lo
00
Sub-function Lo
00
Data Hi
A5
Data Hi
A5
Data Lo
37
Data Lo
27
The data fields in responses to other kinds of queries could contain error counts
or other data requested by the sub-function code.