Read_Var errors in modbus/TCP communication with M340 PLC

Hi,
I'm using a read_var command on a Schneider M340 PLC to communicate with another M340 PLC in the network.
The communication is working fine most of the time, but once in a while (every hour or so) I get an error (number 0x07 = Generic transmission interruption ) and the read_var fails.
If this error occurs, it remains for several retries, and then after a while (without doing anything special, other than retrying) the communication is back on again.
I must mention the communication channel between the two PLCs is stable all the time with/without the read_var error (a ping test does not show any timeout).
Anyone familiar with this error?
Your help will be much appreciated.

Regards,
Assaf

Anyone?

You probably have too many messages at the same time, maybe retriggering the read var function too quickly too often. The CPU ethernet port can only have 6 channels open at one time.
If you have a NOE module it is much easier to use the io scanning capability to pass the data between plcs

GeoffC hi,
Thanks for your reply.

I verified this issue and made sure it's not that.
I have 3 devices I am communicating with and while one of the devices returns error 7, the other 2 works perfectly.
I guess that means it is not maximum connection issue. It's something specific to that connection.
The error 7 appears immediately after running the Read_var command (unlike timeout that keeps activity bit in on state, here its turns off immediately...).
I've attached the code I wrote for the read_var.
If you see anything abnormal, I'll be happy to hear.

Regards,
Assaf

GeoffC said:

The CPU ethernet port can only have 6 channels open at one time.

Click to expand...

The Unity documentation says 16 - but no doubt there could be documentation errors. Is the 6 a tested limit you ran across?

IOScanning is definitely much easier to use than the explicit messaging blocks in Unity.

Unfortunately IOScanning is only possible with an NOE which is not available for me in this project. I must deal with the software Read_var...

Regards,
Assaf

The Unity documentation says 16 - but no doubt there could be documentation errors. Is the 6 a tested limit you ran across

Click to expand...

Is the documentation referring to CPU or NOE, I thought CPU was 6 and NOE was 16 or more, I do know that the CPU comms is much less capable than a NOE. The numbers are from memory so forgive me if incorrect.

Try just running the one message to the device that is giving trouble