Diagnostics (Function Code 08) - ProSoft Technology MVI69E-MBTCP User Manual

MVI69E-MBTCP ♦ CompactLogix Platform
Modbus TCP/IP Enhanced Communication Module
The example below is a request to write the value '3' to register 40002 in server
11.
Node Function
Address Code
0B 06
Response
The response to a preset single register request is to re-transmit the query
message after the register has been altered.
Node Function
Address Code
0B 06

7.2.10 Diagnostics (Function Code 08)

This function provides a series of tests for checking the communication system
between a client device and a server, or for checking various internal error
conditions within a server.
The function uses a two-byte sub-function code field in the query to define the
type of test to be performed. The server echoes both the function code and sub-
function code in a normal response. Some of the diagnostics commands cause
data to be returned from the remote device in the data field of a normal response.
In general, issuing a diagnostic function to a remote device does not affect the
running of the user program in the remote device. Device memory bit and
register data addresses are not accessed by the diagnostics. However, certain
functions can optionally reset error counters in some remote devices.
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-MBTCP 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
ProSoft Technology, Inc.
June 28, 2017
Data Start Bit Data Start
High Bit Low
00 01
Data Register Data Register
High Low
00 01
Data Field (Request)
Any
Preset Data Preset Data
Register High Register Low
00 03
Preset Data Preset Data
Register High Register Low
00 03
Data Field (Response)
Echo Request Data
Reference
User Manual
Error Check
Field (2 bytes)
CRC
Error Check
Field (2 bytes)
CRC
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