Index: firmware/App/Modes/OperationModes.h
===================================================================
diff -u -rb64c49fdcf2b6d95e61e63f8e258c4e600935bbd -rf43eb1e9e0803776ec7420b16e1db8760b020bd9
--- firmware/App/Modes/OperationModes.h	(.../OperationModes.h)	(revision b64c49fdcf2b6d95e61e63f8e258c4e600935bbd)
+++ firmware/App/Modes/OperationModes.h	(.../OperationModes.h)	(revision f43eb1e9e0803776ec7420b16e1db8760b020bd9)
@@ -1,4 +1,4 @@
-/**************************************************************************
+/**********************************************************************//**
  *
  *  Copyright (c) 2019-2020 Diality Inc. - All Rights Reserved.
  *
@@ -19,27 +19,40 @@
 
 #include "DGCommon.h"
 
+/**
+ *  @defgroup OperationModes OperationModes
+ *  @brief Operation Modes module.
+ *  Manages the top level operation modes of the DG via a state machine.
+ *
+ *  @addtogroup OperationModes
+ *  @{
+ */
+
 // ********** public definitions **********
 
-typedef enum Op_Modes        // These are in order of priority (highest to lowest)
+/// Enumeration of operation modes.  These are in order of priority (highest to lowest).
+typedef enum Op_Modes
 {
-    MODE_FAUL = 0,            // Fault
-    MODE_SERV,                // Service
-    MODE_INIT,                // Initialization & POST
-    MODE_STAN,                // Standby
-    MODE_FILL,                // Fill mode
-    MODE_DRAI,                // Drain
-    MODE_FLUS,                // Flush
-    MODE_DISI,                // Disinfect
-    MODE_NLEG,                // Not legal
+    MODE_FAUL = 0,            ///< Fault mode.
+    MODE_SERV,                ///< Service mode.
+    MODE_INIT,                ///< Initialization & POST mode.
+    MODE_STAN,                ///< Standby mode - connected to HD.
+    MODE_SOLO,                ///< Standby Solo mode - no HD connected.
+    MODE_FILL,                ///< Fill mode.
+    MODE_DRAI,                ///< Drain mode.
+    MODE_FLUS,                ///< Flush mode.
+    MODE_DISI,                ///< Disinfect mode.
+    MODE_NLEG,                ///< Not legal - an illegal mode transition occurred.
     NUM_OF_MODES
 } OP_MODE;
 
 // ********** public function prototypes **********
 
 void initOperationModes( void );                   // initialize this module
-void execOperationModes( void );                  // execute the operation modes state machine (scheduled periodic call)
+void execOperationModes( void );                   // execute the operation modes state machine (scheduled periodic call)
 void requestNewOperationMode( OP_MODE newMode );   // request a transition to a new operation mode
 OP_MODE getCurrentOperationMode( void );           // get the current operation mode
 
+/**@}*/
+
 #endif