You have field devices (BMS, inverter, thermostat, IO module, thermal pump) that expose valuable status and controls over MODBUS, but your automation stack cannot read them directly or consistently.
#define FC_READ_HOLDING_REGISTERS 0x03 // Read Holding Registers #define FC_READ_INPUT_REGISTERS 0x04 // Read Input Registers #define FC_WRITE_SINGLE_COIL 0x05 // Write Single Coil #define ...