Issue
When using READ_VAR, the GEST Array's second Word of the Array (index 1) is returning error 512 (16#0200) for a 3rd party device.

Product line
EcoStruxure Control Expert, Unity Pro, Modicon M340, Modicon M580, Modicon Premium

Resolution
The GEST management parameter array's second Word of the Array's Most Significant Byte gives the "Operation Report" for the READ_VAR block.
A value of 16#02 reported by this Operation Report means "Incorrect response".
=> This means that the data coming from the 3rd-party Modbus Server device is returned to the PLC with incorrect data or unexpected data from the Server (3rd-party device) for the given request from the READ_VAR block (PLC Client).

The most likely reasons for this are:
1) The device does not support the command that is sent to it from the READ_VAR block.
-> Make sure that you are reading the correct address type. Sometimes the OBJ pin needs to be '%IW' instead of '%MW' or vice versa. (can also be %I or %M)
-> If using Ethernet, it is possible that the index (a.k.a. Device Number / Unit ID) needs to be changed or added in the READ_VAR for the device. Sometimes the device will require an index of 255 (or some other number). You can add this after the Ip address 'Ethernet_port{xxx.xxx.xxx.xxx}255'

2) There is an intermediate device (radio / cellular switch / ethernet switch) that is modifying or garbling the packets to or from the 3rd-party device due to interference or device buffer issues.

Troubleshooting:
Use a packet capturing tool like Wireshark to read the exchanged packets between the PLC and 3rd-party device.
Wireshark has the ability to analyze Modbus TCP packets and will display them highlighted in red if there is an issue with the response from a device.
NOTE: Wireshark and the devices will need to be connected to a physical ethernet switch that is capable of port mirroring.

Documentation
For further reading about the GEST management parameter, see Section: "Management Parameters: Communication and Operation Reports"
from the User Guide:
"EcoStruxure Control Expert - Communication Block Library" User Guide
https://www.se.com/us/en/download/document/33002527K01000/


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Publicado para:Schneider Electric Mexico