Table of Contents

Master Watchdog

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This function works for following Inputs & Outputs:

  • digital inputs
  • digital outputs
  • relay outputs
  • analog inputs
  • analog outputs

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Important:
In Firmware versions 6.26 and older any valid communication will start MWD and refresh the timeout on that section. From version 6.28 reading the configuration will not start the MWD on that section.

How it works

Master Watchdog present on Unipi controllers and extensions modules has non-traditional specialized implementation. It is used for unwanted situations, where the program lost communication with inputs and outputs. This function ensures a safe configuration is set in case of emergency situations (unit failure, communication error or software issues) to prevent damage to controlled devices or any hazards to personnel.

Every section in controller and every extension have an independent MWD. After section microprocessor start, the MWD will start (if enabled) after first read from inputs or write to outputs. From that moment the timer for watchdog is started and every time action is performed that timer is reset. If the timer reaches a time greater than predefined MWD timeout the microprocessor will reboot. After the section's microprocessor restarts, default configuration is used.

When the Master Watchdog triggers and start rebooting the section, every other LED in the top and bottom row of that section will light up. You can see the LED behavior in MWD Led indication.

How to enable MWD

Select the unipi module or extension in the Left panel. In the Properties panel, you can see MWD Section X Enable and MWD Section X Timeout varibles, where X is the section number.

Depending on which type of controller you have, you will be able to see one, two or three of each of these variables. If the variables are omitted, then your controller doesn't have any inputs or outputs, where MWD would make sense.

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Important:
We just changed the configuration of the PLC modules, which is not applicable by simply uploading the solution. To save the configuration, follow the Unipi - Configure Module tutorial.

You can detect if the last start was due to MWD. The MWD reset indication coil will show value 1, if the section or extension was rebooted by MWD. Keep in mind, that this coil must be set to 0 after reading, if you want to have valid indication of MWD reboot.

Defining the default configuration

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Note:
You can find the addresses of Modbus registers mentioned in this article in your device's Modbus map.

If you want to use MWD you need to consider how the outputs will be set, when the MWD reboots the section. You need to set the section's or extension module's outputs to the safe state and then enable coil Save current configuration and use on startup. Following will be saved to default configuration:

Serial bus configuration

For Neuron units: When restarting a section, the default configuration will be used even for serial bus. Keep that in mind if you are using it with MWD enabled. After a section restarts the serial bus need to be configured again.

For Patron units: Serial bus configuration is saved to non-volatile memory, so after section restart the saved configuration is used.