.. _manual_set_on_monitoring_modbus:

set_on_monitoring_modbus (Manual Mode)
------------------------------------------
This section explains how to use :ref:`set_on_monitoring_modbus <set_on_monitoring_modbus>` during **Manual (Teach)** operations  
to **register a callback function** that monitors **Modbus I/O data** exchanged between the robot controller  
and external devices such as PLCs or inverters in real time.

**Typical usage**

- Observe Modbus coil/register states for debugging communication.  
- Monitor real-time signals (e.g., READY, RUN, FAULT, SPEED) from an external PLC or inverter.  
- Log Modbus traffic and diagnose incorrect addresses or value updates.

.. Note::

    - The callback is triggered whenever Modbus data (coil, discrete input, holding, or input register) changes.  
    - Must be registered **after establishing a connection** and after Modbus symbols are defined using :ref:`add_modbus_signal(Manual Mode) <manual_add_modbus_signal>`.  

**Example: Register and handle Modbus monitoring callback**

.. code-block:: cpp

   // 1) Define callback function
   void OnMonitoringModbus(const LPMONITORING_MODBUS pModbusData) {
       for (int i = 0; i < pModbusData->_iRegCount; ++i) {
           printf("[Modbus Monitor] Symbol: %s | Value: %u\n",
                       pModbusData->_tRegister[i]._szSymbol,
                       pModbusData->_tRegister[i]._iValue);
       }
   }

   // Preconditions:
   // - Connection established (open_connection)
   // - Manual (Teach) mode active
   // - Modbus signals registered via add_modbus_signal()

   // 2) Register callback for Modbus monitoring
   drfl.set_on_monitoring_modbus(OnMonitoringModbus);
   printf("[Modbus] Monitoring callback registered.\n");

   // 3) Keep program running to receive updates
   while (true) {
       std::this_thread::sleep_for(std::chrono::seconds(1));
   }

**Tips**

- See :ref:`Rules for callback functions <callback_rules>`.
- Ensure all Modbus tags are registered and reachable to receive consistent monitoring events.  
- Unregister or stop monitoring before disconnecting from the robot controller to avoid dangling callbacks.