Prosoft-technology MVI71-MNET Manuel d'utilisateur télécharger pdf (Page 93)

Reference MVI71-MNET ♦ PLC Platform

User Manual Modbus TCP/IP Interface Module

ProSoft Technology, Inc. Page 93 of 109

June 23, 2009

A server device can, however, be forced into 'Listen Only Mode' in which it will

monitor 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.

The following diagnostic functions are dedicated to serial line devices.

The normal response to the Return Query Data request is to loopback the same

data. The function code and sub-function codes are also echoed.

Request

Function code 1 Byte 0x08

Sub-function 2 Bytes

Data N x 2 Bytes

Response

Function code 1 Byte 0x08

Sub-function 2 Bytes

Data N x 2 Bytes

Error

Error code 1 Byte 0x88

Exception code 1 Byte 01 or 03 or 04

Sub-function codes supported by the serial line devices

Only Sub-functions 00 is supported by the MVI71-MNET 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

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 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

1 2 ... 88 89 90 91 92 93 94 95 96 97 98 ... 108 109

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Prosoft-technology MVI71-MNET Manuel d'utilisateur Page 93