Modbus TCP

Hello
I have a Optimum BF46 milling machine with the step motor CNC kit
I done 5 years ago a first installation of LinuxCNC and use two LPT port to run it

I try to do a new installation and replace the second lpt port by a wago ModbusTCP coupleur (750-362) on a Debian 10 with Preempt-RT kernel and LinuxCNC 2.9

The configuration is done but the Modbus coupler have curious reaction, each 5-10 minutes all digital output is disable during 1 Modbus cycle add after that normally replacedI do a small script in python and pymodbus to do the same think ; in this case, the coupler haven't this bad reaction

Somebody known the cause of this small turn-off digital output during 1 modbus cycle with linuxcnc ?

Thanks

Is there a timeout that you can be adjusted in the coupler. Search for a watchdog.
When all outputs get dissabled that points towards a safery feature.

In coupler, the timeout is removed
The reply state on digital output is disabled, when communication is break/stop, digital output preserve last state
The state of output hal configuration are all of time in good state
That look like at some time an empty tram is sent to the coupler ( and disable all output )
Outputs are reset properly at next cycle

tcpdump or wireshark might help diagnose the issue

This first test was with modmaster in classicladder
I have reviews all ModbusTCP option and understood fonctionnement of mb2hal
I have redo my config with mb2hal and start a new test

With the module mb2hal, the coupler wago running well but i don't known why with modmaster option in classicladder that not work

Thanks