diff --git a/secop/modules.py b/secop/modules.py
index 07c0936..7a98359 100644
--- a/secop/modules.py
+++ b/secop/modules.py
@@ -211,6 +211,10 @@ class Module(object):
             if '$' in v.unit:
                 v.unit = v.unit.replace('$', self.accessibles['value'].unit)
 
+    def isBusy(self):
+        '''helper function for treating substates of BUSY correctly'''
+        # defined even for non drivable (used for dynamic polling)
+        return False
 
     def early_init(self):
         # may be overriden in derived classes to init stuff
@@ -342,6 +346,10 @@ class Drivable(Writable):
         'status' : Override(datatype=TupleOf(EnumType(Status), StringType())),
     }
 
+    def isBusy(self):
+        '''helper function for treating substates of BUSY correctly'''
+        return 300 <= self.status[0] < 400
+
     # improved polling: may poll faster if module is BUSY
     def poll(self, nr=0):
         # poll status first