Index: firmware/App/Modes/ModeStandby.c
===================================================================
diff -u -r499e5de29e706d09f79ba22511068990c4044e84 -rf43eb1e9e0803776ec7420b16e1db8760b020bd9
--- firmware/App/Modes/ModeStandby.c	(.../ModeStandby.c)	(revision 499e5de29e706d09f79ba22511068990c4044e84)
+++ firmware/App/Modes/ModeStandby.c	(.../ModeStandby.c)	(revision f43eb1e9e0803776ec7420b16e1db8760b020bd9)
@@ -1,4 +1,4 @@
-/**************************************************************************
+/**********************************************************************//**
  *
  *  Copyright (c) 2019-2020 Diality Inc. - All Rights Reserved.
  *
@@ -18,11 +18,30 @@
 #include "ModeStandby.h"
 #include "CPLD.h"
 
+/**
+ *  @addtogroup StandbyMode
+ *  @{
+ */
+
+// ********** private definitions **********
+
+/// Enumeration of standby mode states.
+typedef enum Standby_Mode_States
+{
+    STANDBY_MODE_STATE_START = 0,                                       ///< Start standby mode state.
+    STANDBY_MODE_STATE_IDLE,                                            ///< Idle standby mode state.
+    NUM_OF_STANDBY_MODE_STATES                                          ///< Number of standby mode states.
+} STANDBY_MODE_STATE_T;
+
 // ********** private data **********
 
+static STANDBY_MODE_STATE_T standbyState = STANDBY_MODE_STATE_START;    ///< Currently active standby state.
+
 // ********** private function prototypes **********
 
-/*************************************************************************
+STANDBY_MODE_STATE_T handleStandbyIdleState( void );
+
+/*********************************************************************//**
  * @brief initStandbyMode
  * The initStandbyMode function initializes the Standby Mode module.
  * @details
@@ -35,7 +54,7 @@
 {
 }
 
-/*************************************************************************
+/*********************************************************************//**
  * @brief transitionToStandbyMode
  * The transitionToStandbyMode function prepares for transition to standby mode.
  * @details
@@ -46,9 +65,11 @@
  *************************************************************************/
 void transitionToStandbyMode( void )
 {
+    // reset to start state each time we transition to standby mode
+    standbyState = STANDBY_MODE_STATE_START;
 }
 
-/*************************************************************************
+/*********************************************************************//**
  * @brief execStandbyMode
  * The execStandbyMode function executes the Standby Mode state machine.
  * @details
@@ -59,6 +80,47 @@
  *************************************************************************/
 void execStandbyMode( void )
 {
+    // execute current Standby state
+    switch ( standbyState )
+    {
+        case STANDBY_MODE_STATE_START:
+            standbyState = STANDBY_MODE_STATE_IDLE;
+            break;
 
+        case STANDBY_MODE_STATE_IDLE:
+            standbyState = handleStandbyIdleState();
+            break;
+
+        default:
+            SET_ALARM_WITH_2_U32_DATA( ALARM_ID_SOFTWARE_FAULT, 0, standbyState )     // TODO - add s/w fault enum to 1st data param
+            standbyState = STANDBY_MODE_STATE_START;
+            break;
+    }
 }
 
+/*********************************************************************//**
+ * @brief
+ * The handleStandbyIdleState function executes the Idle state of the \n
+ * Standby Mode state machine.
+ * @details
+ * Inputs : none
+ * Outputs :
+ * @param none
+ * @return the next state
+ *************************************************************************/
+STANDBY_MODE_STATE_T handleStandbyIdleState( void )
+{
+    STANDBY_MODE_STATE_T result = STANDBY_MODE_STATE_IDLE;
+
+    // go to standby or standby solo mode depending on whether HD is connected
+//    if ( FALSE == isHDCommunicating() )  // TODO - handle switching between standby and standby-solo modes
+//    {
+//        requestNewOperationMode( MODE_SOLO );
+//    }
+
+    // TODO - what is DG supposed to be doing while in standby mode?
+
+    return result;
+}
+
+/**@}*/