Index: firmware/App/Services/PIControllers.c
===================================================================
diff -u -rd91a24c730aeb5cd7e3eba9ef4eca78e442911f8 -r0ca8364b86f7b7d7841bc884eae5f674fd5618d4
--- firmware/App/Services/PIControllers.c	(.../PIControllers.c)	(revision d91a24c730aeb5cd7e3eba9ef4eca78e442911f8)
+++ firmware/App/Services/PIControllers.c	(.../PIControllers.c)	(revision 0ca8364b86f7b7d7841bc884eae5f674fd5618d4)
@@ -30,32 +30,43 @@
 /// minimum integral coefficient - cannot be zero.
 #define MIN_KI                      NEARLY_ZERO
 
+/// Enumeration of PI controller direction.
+typedef enum controller_Directions
+{
+    CONTROLLER_BIDIRECTIONAL = 0,           ///< Controller runs bidirectional so it covers positive and negative control signals
+    CONTROLLER_UNIDIRECTIONAL,              ///< Controller run unidirectional so it only covers positive control signals
+    NUM_OF_CONTROLLELR_DIRECTIONS           ///< Number of PI controllers directions
+} PI_CONTROLLER_DIRECTIONS_T;
+
 /// record for PI controller.
 typedef struct {
     // -- PI's parameters --
-    F32 Kp;                         ///< Proportional Value.
-    F32 Ki;                         ///< Integral Value.
-    F32 uMax;                       ///< Maximum control signal.
-    F32 uMin;                       ///< Minimum control signal.
+    F32 Kp;                                 ///< Proportional Value.
+    F32 Ki;                                 ///< Integral Value.
+    F32 uMax;                               ///< Maximum control signal.
+    F32 uMin;                               ///< Minimum control signal.
     // -- PI's signals --
-    F32 referenceSignal;            ///< reference signal.
-    F32 measuredSignal;             ///< measured signal.
-    F32 errorSignal;                ///< reference - measured signal.
-    F32 errorSumBeforeWindUp;       ///< error signal before windup correction.
-    F32 errorSum;                   ///< error integral after windup correction.
-    F32 controlSignal;              ///< actual control signal.
+    F32 referenceSignal;                    ///< reference signal.
+    F32 measuredSignal;                     ///< measured signal.
+    F32 errorSignal;                        ///< reference - measured signal.
+    F32 errorSumBeforeWindUp;               ///< error signal before windup correction.
+    F32 errorSum;                           ///< error integral after windup correction.
+    F32 controlSignal;                      ///< actual control signal.
+    F32 maxErrorSumStep;                    ///< maximum change in I (error sum) for a single control interval.
+    PI_CONTROLLER_DIRECTIONS_T direction;   ///< PI controller control direction.
 } PI_CONTROLLER_T;
+
+/// macro to set a local controller pointer to a given piController.
+#define SET_CONTROLLER( c, id )     ((c) = &piControllers[id])
 
-#define SET_CONTROLLER( c, id )     ((c) = &piControllers[id])          ///< macro to set a local controller pointer to a given piController.
-
 // ********** private data **********
 
 /// PI Controllers -- initial configurations.
 static PI_CONTROLLER_T piControllers[ NUM_OF_PI_CONTROLLERS_IDS ] =
-{   // Kp   Ki  uMax  uMin  ref meas  err  esw esum ctrl
-    { 0.0, 0.0,  1.0,  0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 },  // PI_CONTROLLER_ID_ULTRAFILTRATION
-    { 0.0, 0.0, 0.90, 0.10, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 },  // PI_CONTROLLER_ID_BLOOD_FLOW
-    { 0.0, 0.0, 0.90, 0.10, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 }   // PI_CONTROLLER_ID_DIALYSATE_FLOW
+{   // Kp   Ki  uMax  uMin  ref meas  err  esw esum ctrl  Ilimit controller type
+    { 0.0, 0.0,  1.0,  0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 10.0,  CONTROLLER_UNIDIRECTIONAL },  // PI_CONTROLLER_ID_ULTRAFILTRATION
+    { 0.0, 0.0, 0.90, 0.10, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 100.0, CONTROLLER_UNIDIRECTIONAL },  // PI_CONTROLLER_ID_BLOOD_FLOW
+    { 0.0, 0.0, 0.90, 0.10, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 100.0, CONTROLLER_UNIDIRECTIONAL }   // PI_CONTROLLER_ID_DIALYSATE_FLOW
 };
 
 /**@}*/
@@ -148,28 +159,54 @@
     F32 result = 0.0;
 
     if ( controllerID < NUM_OF_PI_CONTROLLERS_IDS )
-    {
+    {
         F32 controlSignalBeforeWindup;
         F32 windupError;
 
         SET_CONTROLLER( controller, controllerID );
 
         controller->referenceSignal = referenceSignal;
-        controller->measuredSignal = measuredSignal;
+        controller->measuredSignal = measuredSignal;
+
         // calculate error signal
-        controller->errorSignal = fabs( referenceSignal ) - ( referenceSignal < 0.0 ? ( measuredSignal * -1.0 ) : measuredSignal );
-        controller->errorSum += controller->errorSignal;
-        // anti-windup
-        controller->errorSumBeforeWindUp = controller->errorSum;
+        if ( controller->direction == CONTROLLER_UNIDIRECTIONAL )
+        {
+            controller->errorSignal = fabs( referenceSignal ) - ( referenceSignal < 0.0 ? ( measuredSignal * -1.0 ) : measuredSignal );
+        }
+        else
+        {
+            controller->errorSignal = referenceSignal - measuredSignal;
+        }
+
+        // limit error sum step size
+        if ( fabs( controller->errorSignal ) > controller->maxErrorSumStep )
+        {
+            if ( controller->errorSignal < 0.0 )
+            {
+                controller->errorSum += ( controller->maxErrorSumStep * -1.0 );
+            }
+            else
+            {
+                controller->errorSum += controller->maxErrorSumStep;
+            }
+        }
+        else
+        {
+            controller->errorSum += controller->errorSignal;
+        }
+
         // calculate control signal
+        controller->errorSumBeforeWindUp = controller->errorSum;
         controlSignalBeforeWindup = ( controller->Kp * controller->errorSignal ) + ( controller->Ki * controller->errorSum );
-        controller->controlSignal = RANGE( controlSignalBeforeWindup, controller->uMin, controller->uMax );
+        controller->controlSignal = RANGE( controlSignalBeforeWindup, controller->uMin, controller->uMax );
+
         // handle anti-windup for i term
         windupError = controlSignalBeforeWindup - controller->controlSignal;
         if ( fabs( windupError ) > NEARLY_ZERO )
         {
             controller->errorSum -= ( windupError / controller->Ki );
-        }
+        }
+
         result = controller->controlSignal;
     }
     else