diff --git a/core/src/drivers/plugins/python/modbus_master/modbus_master_connection.py b/core/src/drivers/plugins/python/modbus_master/modbus_master_connection.py
index e9c81a5d..f1ba0ccb 100644
--- a/core/src/drivers/plugins/python/modbus_master/modbus_master_connection.py
+++ b/core/src/drivers/plugins/python/modbus_master/modbus_master_connection.py
@@ -9,10 +9,11 @@
 class ModbusConnectionManager:  # pylint: disable=too-many-instance-attributes
     """Manages Modbus TCP connections with retry logic."""
 
-    def __init__(self, host: str, port: int, timeout_ms: int):
+    def __init__(self, host: str, port: int, timeout_ms: int, slave_id: int = 1):
         self.host = host
         self.port = port
         self.timeout = timeout_ms / 1000.0  # Convert to seconds
+        self.slave_id = slave_id  # Unit/Slave ID for Modbus TCP gateways
 
         # Retry configuration
         self.retry_delay_base = 2.0  # initial delay between attempts (seconds)
diff --git a/core/src/drivers/plugins/python/modbus_master/modbus_master_plugin.py b/core/src/drivers/plugins/python/modbus_master/modbus_master_plugin.py
index b494b70e..ab66a566 100644
--- a/core/src/drivers/plugins/python/modbus_master/modbus_master_plugin.py
+++ b/core/src/drivers/plugins/python/modbus_master/modbus_master_plugin.py
@@ -74,7 +74,7 @@ def __init__(self, device_config: Any, sba: SafeBufferAccess, plugin_logger: Plu
         self.logger = plugin_logger
         self._stop_event = threading.Event()
         self.connection_manager = ModbusConnectionManager(
-            device_config.host, device_config.port, device_config.timeout_ms
+            device_config.host, device_config.port, device_config.timeout_ms, device_config.slave_id
         )
         self.name = f"ModbusSlave-{device_config.name}-{device_config.host}:{device_config.port}"
 
@@ -149,22 +149,23 @@ def run(self):  # pylint: disable=too-many-locals
                             count = point.length  # 1:1 mapping for boolean operations
 
                         # Perform Modbus read based on function code
-                        # Note: pymodbus 3.x requires count as keyword argument
+                        # Note: pymodbus 3.10+ uses device_id parameter (formerly slave)
+                        # device_id is used for Modbus TCP gateways that forward to RS485 devices
                         if point.fc == 1:  # Read Coils
                             response = self.connection_manager.client.read_coils(
-                                address, count=count
+                                address, count=count, device_id=self.connection_manager.slave_id
                             )
                         elif point.fc == 2:  # Read Discrete Inputs
                             response = self.connection_manager.client.read_discrete_inputs(
-                                address, count=count
+                                address, count=count, device_id=self.connection_manager.slave_id
                             )
                         elif point.fc == 3:  # Read Holding Registers
                             response = self.connection_manager.client.read_holding_registers(
-                                address, count=count
+                                address, count=count, device_id=self.connection_manager.slave_id
                             )
                         elif point.fc == 4:  # Read Input Registers
                             response = self.connection_manager.client.read_input_registers(
-                                address, count=count
+                                address, count=count, device_id=self.connection_manager.slave_id
                             )
                         else:
                             self.logger.warn(f"[{self.name}] Unsupported read FC: {point.fc}")
@@ -327,10 +328,12 @@ def run(self):  # pylint: disable=too-many-locals
                             continue
 
                         # Perform Modbus write operation
+                        # Note: pymodbus 3.10+ uses device_id parameter (formerly slave)
+                        # device_id is used for Modbus TCP gateways that forward to RS485 devices
                         if point.fc == 5:  # Write Single Coil
                             if len(values_to_write) > 0:
                                 response = self.connection_manager.client.write_coil(
-                                    address, values_to_write[0]
+                                    address, values_to_write[0], device_id=self.connection_manager.slave_id
                                 )
                             else:
                                 self.logger.error(
@@ -341,7 +344,7 @@ def run(self):  # pylint: disable=too-many-locals
                         elif point.fc == 6:  # Write Single Register
                             if len(values_to_write) > 0:
                                 response = self.connection_manager.client.write_register(
-                                    address, values_to_write[0]
+                                    address, values_to_write[0], device_id=self.connection_manager.slave_id
                                 )
                             else:
                                 self.logger.error(
@@ -351,11 +354,11 @@ def run(self):  # pylint: disable=too-many-locals
                                 continue
                         elif point.fc == 15:  # Write Multiple Coils
                             response = self.connection_manager.client.write_coils(
-                                address, values_to_write
+                                address, values_to_write, device_id=self.connection_manager.slave_id
                             )
                         elif point.fc == 16:  # Write Multiple Registers
                             response = self.connection_manager.client.write_registers(
-                                address, values_to_write
+                                address, values_to_write, device_id=self.connection_manager.slave_id
                             )
                         else:
                             self.logger.warn(f"[{self.name}] Unsupported write FC: {point.fc}")
diff --git a/core/src/drivers/plugins/python/shared/plugin_config_decode/modbus_master_config_model.py b/core/src/drivers/plugins/python/shared/plugin_config_decode/modbus_master_config_model.py
index e848b1a6..b8c63587 100644
--- a/core/src/drivers/plugins/python/shared/plugin_config_decode/modbus_master_config_model.py
+++ b/core/src/drivers/plugins/python/shared/plugin_config_decode/modbus_master_config_model.py
@@ -73,6 +73,7 @@ def __init__(self):
         self.host: str = "127.0.0.1"
         self.port: int = 502
         self.timeout_ms: int = 1000
+        self.slave_id: int = 1  # Unit/Slave ID for Modbus TCP gateways (0-255)
         self.io_points: List['ModbusIoPointConfig'] = []
 
     @classmethod
@@ -89,6 +90,7 @@ def from_dict(cls, data: Dict[str, Any]) -> 'ModbusDeviceConfig':
         device.host = config.get("host", "127.0.0.1")
         device.port = config.get("port", 502)
         device.timeout_ms = config.get("timeout_ms", 1000)
+        device.slave_id = config.get("slave_id", 1)
 
         # Parse I/O points
         io_points_data = config.get("io_points", [])
@@ -110,6 +112,8 @@ def validate(self) -> None:
             raise ValueError(f"Invalid port: {self.port}. Must be a positive integer for device {self.name}.")
         if not isinstance(self.timeout_ms, int) or self.timeout_ms <= 0:
             raise ValueError(f"Invalid timeout_ms: {self.timeout_ms}. Must be a positive integer for device {self.name}.")
+        if not isinstance(self.slave_id, int) or not (0 <= self.slave_id <= 255):
+            raise ValueError(f"Invalid slave_id: {self.slave_id}. Must be an integer between 0 and 255 for device {self.name}.")
 
         for i, point in enumerate(self.io_points):
             if not isinstance(point, ModbusIoPointConfig):
@@ -126,7 +130,7 @@ def validate(self) -> None:
                 raise ValueError(f"Invalid cycle_time_ms: {point.cycle_time_ms}. Must be a positive integer for device {self.name}, point {i}.")
 
     def __repr__(self) -> str:
-        return f"ModbusDeviceConfig(name='{self.name}', host='{self.host}', port={self.port}, io_points={len(self.io_points)})"
+        return f"ModbusDeviceConfig(name='{self.name}', host='{self.host}', port={self.port}, slave_id={self.slave_id}, io_points={len(self.io_points)})"
 
 class ModbusMasterConfig(PluginConfigContract):
     """