diff -r e4ab768170f9 -r db68cb0e6bdc runtime/PLCObject.py
--- a/runtime/PLCObject.py	Thu May 28 11:01:42 2020 +0100
+++ b/runtime/PLCObject.py	Thu May 28 11:15:22 2020 +0100
@@ -99,6 +99,9 @@
         self.TraceLock = Lock()
         self.Traces = []
         self.DebugToken = 0
+        # Callbacks used by web settings extensions (e.g.: BACnet_config.py, Modbus_config.py)
+        self.LoadCallbacks   = {} # list of functions to call when PLC is   loaded
+        self.UnLoadCallbacks = {} # list of functions to call when PLC is unloaded
 
         self._init_blobs()
 
@@ -167,6 +170,22 @@
             return self._loading_error, 0, 0, 0
         return None
 
+    def RegisterCallbackLoad(self, ExtensionName, ExtensionCallback):
+        """
+        Register function to be called when PLC is loaded
+        ExtensionName: a string with the name of the extension asking to register the callback 
+        ExtensionCallback: the function to be called...
+        """
+        self.LoadCallbacks[ExtensionName] = ExtensionCallback
+
+    def RegisterCallbackUnLoad(self, ExtensionName, ExtensionCallback):
+        """
+        Register function to be called when PLC is unloaded
+        ExtensionName: a string with the name of the extension asking to register the callback 
+        ExtensionCallback: the function to be called...
+        """
+        self.UnLoadCallbacks[ExtensionName] = ExtensionCallback
+
     def _GetMD5FileName(self):
         return os.path.join(self.workingdir, "lasttransferedPLC.md5")
 
@@ -270,6 +289,8 @@
         res = self._LoadPLC()
         if res:
             self.PythonRuntimeInit()
+            for name, callbackFunc in self.LoadCallbacks.items():
+                callbackFunc()
         else:
             self._FreePLC()
 
@@ -278,6 +299,8 @@
     @RunInMain
     def UnLoadPLC(self):
         self.PythonRuntimeCleanup()
+        for name, callbackFunc in self.UnLoadCallbacks.items():
+            callbackFunc()        
         self._FreePLC()
 
     def _InitPLCStubCalls(self):