ProSoft Technology MVI69E-MBTCP User Manual

Page 117

MVI69E-MBTCP ♦ CompactLogix Platform

Reference

Modbus TCP/IP Enhanced Communication Module

User Manual

ProSoft Technology, Inc.

Page 117 of 150

May 20, 2015

Response
The response to a preset single register request is to re-transmit the query
message after the register has been altered.

Node

Address

Function

Code

Data Register

High

Data Register

Low

Preset Data

Register High

Preset Data

Register Low

Error Check

Field (2 bytes)

CRC

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

Data Field (Request)

Data Field (Response)

00 00

Any

Echo Request Data