diff --git a/frappy_psi/parmod.py b/frappy_psi/parmod.py
index 31d60e0..1b6fe3c 100644
--- a/frappy_psi/parmod.py
+++ b/frappy_psi/parmod.py
@@ -22,7 +22,7 @@
 """modules to access parameters"""
 
 from frappy.core import Drivable, EnumType, IDLE, Attached, StringType, Property, \
-    Parameter, FloatRange, BoolType, Readable, ERROR
+    Parameter, BoolType, FloatRange, Readable, ERROR, nopoll
 from frappy.errors import ConfigError
 from frappy_psi.convergence import HasConvergence
 from frappy_psi.mixins import HasRamp
@@ -72,19 +72,21 @@ class Driv(Drivable):
             raise ConfigError('illegal recursive read/write module')
         super().checkProperties()
 
-    #def registerUpdates(self):
-    #    self.read.valueCallbacks[self.read_param].append(self.update_value)
-    #    self.write.valueCallbacks[self.write_param].append(self.update_target)
-    #
-    #def startModule(self, start_events):
-    #    start_events.queue(self.registerUpdates)
-    #    super().startModule(start_events)
+    def registerUpdates(self):
+        self.read.addCallback(self.read_param, self.announceUpdate, 'value')
+        self.write.addCallback(self.write_param, self.announceUpdate, 'target')
 
+    def startModule(self, start_events):
+        start_events.queue(self.registerUpdates)
+        super().startModule(start_events)
+
+    @nopoll
     def read_value(self):
-        return getattr(self.read, f'{self.read_param}')
+        return getattr(self.read, f'read_{self.read_param}')()
 
+    @nopoll
     def read_target(self):
-        return getattr(self.write, f'{self.write_param}')
+        return getattr(self.write, f'read_{self.write_param}')()
 
     def read_status(self):
         return IDLE, ''
@@ -130,7 +132,7 @@ def set_enabled(modobj, value):
 
 
 def get_value(obj, default):
-    """get the value of given module. if not valid, return the limit (min_high or max_low)"""
+    """get the value of given module. if not valid, return the default"""
     if not getattr(obj, 'enabled', True):
         return default
     # consider also that a value 0 is invalid