Index: firmware/App/Services/TDInterface.c
===================================================================
diff -u -rbd522c8ffdf75130571e5b6a79d1b1d6acd78b1c -r1a15aa462c0db129606243a4761fa2978ce01730
--- firmware/App/Services/TDInterface.c	(.../TDInterface.c)	(revision bd522c8ffdf75130571e5b6a79d1b1d6acd78b1c)
+++ firmware/App/Services/TDInterface.c	(.../TDInterface.c)	(revision 1a15aa462c0db129606243a4761fa2978ce01730)
@@ -93,7 +93,7 @@
 // TD status
 static TD_OP_MODE_T tdCurrentOpMode;                                       ///< Current TD operation mode.
 static U32 tdSubMode;                                                      ///< Current state (sub-mode) of current TD operation mode.
-static BOOL tdDialyzerBypass;                                              ///< TD dialyzer bypass
+static U32 tdRequestedGenDState;                                           ///< TD-requested gen dialysate sub-state (DD_GEND_MODE_STATE_T).
 static BOOL tdOpModeDataFreshFlag = FALSE;                                 ///< Flag to signal/process fresh TD op mode data
 
 static OVERRIDE_F32_T tdDialysateFlowrate;                                 ///< TD Dialysate flow rate
@@ -108,6 +108,7 @@
 // ********** private function prototypes **********
 
 static void checkTDDataFreshness( ALARM_ID_T alarmID, BOOL *tdFreshDataFlag );
+static BOOL isValidTDGenDStateRequest( U32 genDialysateState );
 
 /*********************************************************************//**
  * @brief
@@ -119,10 +120,10 @@
 void initTDInterface( void )
 {
     // Initialize unit state variables
-    tdCurrentOpMode                     = MODE_INIT;
-    tdSubMode                           = 0U;
-    tdDialyzerBypass                    = FALSE;
-    tdOpModeDataFreshFlag               = FALSE;
+    tdCurrentOpMode                = MODE_INIT;
+    tdSubMode                      = 0U;
+    tdRequestedGenDState           = DD_GEND_DIALYSATE_BYPASS_STATE;
+    tdOpModeDataFreshFlag          = FALSE;
 
     // Initialize treatment parameters from TD
     tdDialysateFlowrate.data            = 0.0F;
@@ -201,6 +202,31 @@
 
 /*********************************************************************//**
  * @brief
+ * The isValidTDGenDStateRequest function validates a TD gen dialysate
+ * sub-state request.
+ * @details \b Inputs: genDialysateState
+ * @details \b Outputs: none
+ * @param genDialysateState Requested DD gen dialysate sub-state.
+ * @return TRUE if the request is a TD-commandable treatment sub-state
+ * (bypass, delivery, or isolated UF). Internal DD states such as spent/
+ * bicarb chamber fill and delivery pause are not TD-requestable.
+ *************************************************************************/
+static BOOL isValidTDGenDStateRequest( U32 genDialysateState )
+{
+    BOOL result = FALSE;
+
+    if ( ( DD_GEND_DIALYSATE_BYPASS_STATE == genDialysateState ) ||
+         ( DD_GEND_DIALYSATE_DELIVERY_STATE == genDialysateState ) ||
+         ( DD_GEND_ISOLATED_UF_STATE == genDialysateState ) )
+    {
+        result = TRUE;
+    }
+
+    return result;
+}
+
+/*********************************************************************//**
+ * @brief
  * The execTDInterfaceMonitor function executes the TD Interface monitoring
  * function.  Ensures TD is sending fresh data in a timely manner.
  * @details \b Inputs: none
@@ -306,16 +332,25 @@
 
 /*********************************************************************//**
  * @brief
- * The setTDDialyzerBypass function sets the latest TD dialyzer bypass
- * enable.
+ * The setTDRequestedGenDState function sets the latest TD-requested gen
+ * dialysate sub-state.
+ * @details \b Alarm: ALARM_ID_DD_SOFTWARE_FAULT if requested state is not
+ * a TD-commandable gen dialysate sub-state.
  * @details \b Inputs: none
- * @details \b Outputs: tdDialyzerBypass
- * @param Dialyzer Bypass enable.
+ * @details \b Outputs: tdRequestedGenDState
+ * @param genDialysateState Requested DD gen dialysate sub-state.
  * @return none.
  *************************************************************************/
-void setTDDialyzerBypass( BOOL dialBypass )
+void setTDRequestedGenDState( U32 genDialysateState )
 {
-    tdDialyzerBypass = dialBypass;
+    if ( TRUE == isValidTDGenDStateRequest( genDialysateState ) )
+    {
+        tdRequestedGenDState = genDialysateState;
+    }
+    else
+    {
+        SET_ALARM_WITH_2_U32_DATA( ALARM_ID_DD_SOFTWARE_FAULT, SW_FAULT_ID_INVALID_TD_GEND_STATE_REQUEST, genDialysateState );
+    }
 }
 
 /*********************************************************************//**
@@ -389,15 +424,15 @@
 }
 /*********************************************************************//**
  * @brief
- * The getTDDialyzerBypass function gets the latest TD dailyzer bypass valve
- * enable flag.
- * @details \b Inputs: tdDialyzerBypass
+ * The getTDRequestedGenDState function gets the latest TD-requested gen
+ * dialysate sub-state.
+ * @details \b Inputs: tdRequestedGenDState
  * @details \b Outputs: none
- * @return Latest dialyzer bypass valve enable.
+ * @return Latest requested gen dialysate sub-state.
  *************************************************************************/
-BOOL getTDDialyzerBypass( void )
+U32 getTDRequestedGenDState( void )
 {
-    return tdDialyzerBypass;
+    return tdRequestedGenDState;
 }
 
 /******************************************************************************
@@ -558,12 +593,10 @@
             setTDUFRate( startTxRequest.ufRate );
             setTDTargetDialysateTemperature( startTxRequest.dialTemp );
 
-            // Set concentrate types, Bypass dialyzer and substitution rate
+            // Set concentrate types and requested gen dialysate sub-state
             setTDAcidAndBicarbType( startTxRequest.acidConvFactor, startTxRequest.bicarbConvFactor,
                                     startTxRequest.sodium, startTxRequest.bicarbonate );
-            setTDDialyzerBypass( startTxRequest.bypassDialyzer );
-            tdSubstitutionFlowRate.data = startTxRequest.substitutionRate;
-            setSubstitutionPumpTargetRate( D92_PUMP,  getTDSubstitutionFlowRate() );
+            setTDRequestedGenDState( startTxRequest.genDialysateState );
 
             // start dialysate generation
             result = requestDDGenDialStart();
@@ -589,12 +622,10 @@
                 setTDUFRate( startTxRequest.ufRate );
                 setTDTargetDialysateTemperature( startTxRequest.dialTemp );
 
-                // Set concentrate types, Bypass dialyzer and substitution rate
+                // Set concentrate types and requested gen dialysate sub-state
                 setTDAcidAndBicarbType( startTxRequest.acidConvFactor, startTxRequest.bicarbConvFactor,
                                         startTxRequest.sodium, startTxRequest.bicarbonate );
-                setTDDialyzerBypass( startTxRequest.bypassDialyzer );
-                tdSubstitutionFlowRate.data = startTxRequest.substitutionRate;
-                setSubstitutionPumpTargetRate( D92_PUMP,  getTDSubstitutionFlowRate() );
+                setTDRequestedGenDState( startTxRequest.genDialysateState );
 
                 // Signal to update treatement parameters
                 setTreatmentParamUpdate();