diff --git a/src/ProcessImage.py b/src/ProcessImage.py
index 50dc546..50d91fb 100644
--- a/src/ProcessImage.py
+++ b/src/ProcessImage.py
@@ -16,6 +16,8 @@ class ProcessImage(Condition):
         self.numCoils = numCoils
         self.coils = []
         self.shadowCoils = [ None ] * numCoils
+        self.readCoils = [ None ] * numCoils
+        self.readShadowCoils = [ None ] * numCoils
 
         self.numDiscreteInputs = numDiscreteInputs
         self.discreteInputs = []
@@ -31,7 +33,7 @@ class ProcessImage(Condition):
         return self.initialized
 
     def hasPendingInputChanges(self):
-        return (self.discreteInputs != self.shadowDiscreteInputs) or (self.analogInputs != self.shadowAnalogInputs)
+        return (self.discreteInputs != self.shadowDiscreteInputs) or (self.analogInputs != self.shadowAnalogInputs) or (self.readCoils != self.readShadowCoils)
 
     def hasPendingOutputChanges(self):
         return self.shadowCoils != self.coils
@@ -56,7 +58,9 @@ class ProcessImage(Condition):
     def setCoils(self, coils):
         if not self.initialized:
             raise NotInitializedException
-        self.coils = coils
+        self.readCoils = coils
+        if self.coils == []:
+            self.coils = coils
 
     def setCoil(self, coilNum, value):
         if not self.initialized:
@@ -67,8 +71,8 @@ class ProcessImage(Condition):
     def getChangedCoils(self):
         if not self.initialized:
             raise NotInitializedException
-        changedCoils = zippingFilter(self.coils, self.shadowCoils)
-#        self.shadowCoils = self.coils
+        changedCoils = zippingFilter(self.coils, self.readCoils)
+        self.readShadowCoils = self.coils
         return changedCoils
     
     def getCoils(self):