This example demonstrates using the port of the FreeModbus stack on an ESP32 target where the ESP32 target is operating as a network slave. The example allows an external Modbus host to read/write device parameters on the ESP32 target using the Modbus protocol. The parameters accessible through Modbus are located in `mb_example_common/modbus_params.h\c` source/header files that users can update to add/remove their own custom parameters.
These are represented in structures `holding_reg_params`, `input_reg_params`, `coil_reg_params`, `discrete_reg_params` for holding registers, input parameters, coils and discrete inputs accordingly. The app_main application demonstrates how to setup Modbus stack and use notifications about parameters change from host system.
The FreeModbus stack located in `components/freemodbus` folder and contains the `/port` folder where the stack's port to the ESP32 is situated. There are some parameters of the port that can be configured in KConfig file to start stack correctly (See description below for more information).
Note: The ```Example Data (Object) Dictionary``` in the modbus_master example can be edited to address parameters from other slaves connected into Modbus segment.
Note: Each target chip has different GPIO pins available for UART connection. Please refer to UART documentation for selected target for more information.
Define the ```Modbus communiction mode``` for slave in Kconfig - CONFIG_MB_COMM_MODE (must be the same for master and slave application).
Set ```Modbus slave address``` for the example application (by default for example script is set to 1).
The communication parameters of freemodbus stack (Component config->Modbus configuration) allow to configure it appropriately but usually it is enough to use default settings.
See the help strings of parameters for more information.
Note: The ```Modbus communiction mode``` parameter must be the same for master and slave example application to be able to communicate with each other.
The output lines describe type of operation, its timestamp, modbus address, access type, storage address in parameter structure and number of registers accordingly.
