How to detect Modbus Communication Failure at Modicon M580?

[RuchirSomani]

Hi,

I need to understand how to find/configured in Control Expert for M580 whether Modbus Communication with any Modbus Slave device is working or has stopped ?
Is there any fail/error bit/code to sense this ?

Right now as values gets transferred between M580 and PSO over Modbus TCP,  the value gets stuck in PSO if downstream devices stop communication with M580 for any reason.
Is it also possible to convert this value automatically to "ZERO" in case the Modbus communication with field device breaks.

[Hennie_Smith]

Good day,

1. Yes you can monitor the Freshness bit in the Device DDT variable which is created when adding modbus device.

Secondly to set the values to 0 if comms fail, open the NOC/CPU in the DTM browser and go to the Request settings of the modbus device. Each request can be set to 'Set to Zero' under the Last Value column. 

Regards,

Hennie Smith

[YONGHO-KIM]

1. I have implemented communication fault/normal status detection using the 'Gest' value from Read_Var.
The second word of the GEST value is 0 when communication is normal, and any value greater than 0 indicates an error.
Please refer to the attached PDF file for more details, and feel free to contact us if you have any questions.