diff --git a/DCCACK.cpp b/DCCACK.cpp
index 1b339ee..8a074b4 100644
--- a/DCCACK.cpp
+++ b/DCCACK.cpp
@@ -351,7 +351,7 @@ void DCCACK::callback(int value) {
 
     switch (callbackState) {
       case AFTER_READ:
-         if (ackManagerRejoin && autoPowerOff) {
+         if (ackManagerRejoin && !autoPowerOff) {
                 progDriver->setPower(POWERMODE::OFF);
                 callbackStart=millis();
                 callbackState=WAITING_30;
diff --git a/DCCEXParser.cpp b/DCCEXParser.cpp
index aaf733c..53cb5ce 100644
--- a/DCCEXParser.cpp
+++ b/DCCEXParser.cpp
@@ -25,6 +25,79 @@
  *  You should have received a copy of the GNU General Public License
  *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
  */
+
+/*
+List of single character OPCODEs in use for reference.
+
+When determining a new OPCODE for a new feature, refer to this list as the source of truth.
+
+Once a new OPCODE is decided upon, update this list.
+
+  Character, Usage
+  /, |EX-R| interactive commands
+  -, Remove from reminder table
+  =, |TM| configuration
+  !, Emergency stop
+  @, Reserved for future use - LCD messages to JMRI
+  #, Request number of supported cabs/locos; heartbeat
+  +, WiFi AT commands
+  ?, Reserved for future use
+  0, Track power off
+  1, Track power on
+  a, DCC accessory control
+  A,
+  b, Write CV bit on main
+  B, Write CV bit
+  c, Request current command
+  C,
+  d,
+  D, Diagnostic commands
+  e, Erase EEPROM
+  E, Store configuration in EEPROM
+  f, Loco decoder function control (deprecated)
+  F, Loco decoder function control
+  g,
+  G,
+  h,
+  H, Turnout state broadcast
+  i, Reserved for future use - Turntable object broadcast
+  I, Reserved for future use - Turntable object command and control
+  j, Throttle responses
+  J, Throttle queries
+  k, Reserved for future use - Potentially Railcom
+  K, Reserved for future use - Potentially Railcom
+  l, Loco speedbyte/function map broadcast
+  L,
+  m,
+  M, Write DCC packet
+  n,
+  N,
+  o,
+  O, Output broadcast
+  p, Broadcast power state
+  P, Write DCC packet
+  q, Sensor deactivated
+  Q, Sensor activated
+  r, Broadcast address read on programming track
+  R, Read CVs
+  s, Display status
+  S, Sensor configuration
+  t, Cab/loco update command
+  T, Turnout configuration/control
+  u, Reserved for user commands
+  U, Reserved for user commands
+  v,
+  V, Verify CVs
+  w, Write CV on main
+  W, Write CV
+  x,
+  X, Invalid command
+  y,
+  Y, Output broadcast
+  z,
+  Z, Output configuration/control
+*/
+
 #include "StringFormatter.h"
 #include "DCCEXParser.h"
 #include "DCC.h"
@@ -378,12 +451,16 @@ void DCCEXParser::parseOne(Print *stream, byte *com, RingStream * ringStream)
 
 #ifndef DISABLE_PROG
     case 'w': // WRITE CV on MAIN <w CAB CV VALUE>
-        DCC::writeCVByteMain(p[0], p[1], p[2]);
-        return;
+      if (params != 3)
+	break;
+      DCC::writeCVByteMain(p[0], p[1], p[2]);
+      return;
 
     case 'b': // WRITE CV BIT ON MAIN <b CAB CV BIT VALUE>
-        DCC::writeCVBitMain(p[0], p[1], p[2], p[3]);
-        return;
+      if (params != 4)
+	break;
+      DCC::writeCVBitMain(p[0], p[1], p[2], p[3]);
+      return;
 #endif
 
     case 'M': // WRITE TRANSPARENT DCC PACKET MAIN <M REG X1 ... X9>
@@ -406,14 +483,16 @@ void DCCEXParser::parseOne(Print *stream, byte *com, RingStream * ringStream)
         
 #ifndef DISABLE_PROG
     case 'W': // WRITE CV ON PROG <W CV VALUE CALLBACKNUM CALLBACKSUB>
-            if (!stashCallback(stream, p, ringStream))
-                break;
+        if (!stashCallback(stream, p, ringStream))
+	    break;
         if (params == 1) // <W id> Write new loco id (clearing consist and managing short/long)
             DCC::setLocoId(p[0],callback_Wloco);
         else if (params == 4)  // WRITE CV ON PROG <W CV VALUE [CALLBACKNUM] [CALLBACKSUB]>
             DCC::writeCVByte(p[0], p[1], callback_W4);
-        else  // WRITE CV ON PROG <W CV VALUE>
+        else if (params == 2)  // WRITE CV ON PROG <W CV VALUE>
             DCC::writeCVByte(p[0], p[1], callback_W);
+	else
+            break;
         return;
 
     case 'V': // VERIFY CV ON PROG <V CV VALUE> <V CV BIT 0|1>
@@ -433,9 +512,11 @@ void DCCEXParser::parseOne(Print *stream, byte *com, RingStream * ringStream)
         }
         break;
 
-    case 'B': // WRITE CV BIT ON PROG <B CV BIT VALUE CALLBACKNUM CALLBACKSUB>
+    case 'B': // WRITE CV BIT ON PROG  <B CV BIT VALUE CALLBACKNUM CALLBACKSUB> or <B CV BIT VALUE>
+        if (params != 3 && params != 5)
+	  break;
         if (!stashCallback(stream, p, ringStream))
-            break;
+	  break;
         DCC::writeCVBit(p[0], p[1], p[2], callback_B);
         return;
 
@@ -565,12 +646,12 @@ void DCCEXParser::parseOne(Print *stream, byte *com, RingStream * ringStream)
     case ' ': // < >
         StringFormatter::send(stream, F("\n"));
         return;
-
+#ifndef DISABLE_DIAG
     case 'D': // < >
         if (parseD(stream, params, p))
             return;
-        return;
-
+        break;
+#endif
     case '=': // <= Track manager control  >
         if (TrackManager::parseJ(stream, params, p))
             return;
diff --git a/EXRAIL2.cpp b/EXRAIL2.cpp
index 95ba6a2..e5509b9 100644
--- a/EXRAIL2.cpp
+++ b/EXRAIL2.cpp
@@ -2,7 +2,7 @@
  *  © 2021 Neil McKechnie
  *  © 2021-2023 Harald Barth
  *  © 2020-2023 Chris Harlow
- *  © 2022 Colin Murdoch
+ *  © 2022-2023 Colin Murdoch
  *  All rights reserved.
  *  
  *  This file is part of CommandStation-EX
@@ -97,6 +97,7 @@ LookList *  RMFT2::onAmberLookup=NULL;
 LookList *  RMFT2::onGreenLookup=NULL;
 LookList *  RMFT2::onChangeLookup=NULL;
 LookList *  RMFT2::onClockLookup=NULL;
+LookList *  RMFT2::onOverloadLookup=NULL;
 
 #define GET_OPCODE GETHIGHFLASH(RMFT2::RouteCode,progCounter)
 #define SKIPOP progCounter+=3
@@ -178,6 +179,7 @@ LookList* RMFT2::LookListLoader(OPCODE op1, OPCODE op2, OPCODE op3) {
   onGreenLookup=LookListLoader(OPCODE_ONGREEN);
   onChangeLookup=LookListLoader(OPCODE_ONCHANGE);
   onClockLookup=LookListLoader(OPCODE_ONTIME);
+  onOverloadLookup=LookListLoader(OPCODE_ONOVERLOAD);
 
 
   // Second pass startup, define any turnouts or servos, set signals red
@@ -198,6 +200,7 @@ LookList* RMFT2::LookListLoader(OPCODE op1, OPCODE op2, OPCODE op3) {
     case OPCODE_AT:
     case OPCODE_ATTIMEOUT2:
     case OPCODE_AFTER:
+    case OPCODE_AFTEROVERLOAD:
     case OPCODE_IF:
     case OPCODE_IFNOT: {
       int16_t pin = (int16_t)operand;
@@ -734,7 +737,17 @@ void RMFT2::loop2() {
     }
     if (millis()-waitAfter < 500 ) return;
     break;
-    
+
+  case OPCODE_AFTEROVERLOAD: // waits for the power to be turned back on - either by power routine or button
+    if (!TrackManager::isPowerOn(operand)) {
+      // reset timer to half a second and keep waiting
+      waitAfter=millis();
+      delayMe(50);
+      return;
+    }
+    if (millis()-waitAfter < 500 ) return;
+    break;
+
   case OPCODE_LATCH:
     setFlag(operand,LATCH_FLAG);
     break;
@@ -1040,6 +1053,7 @@ void RMFT2::loop2() {
   case OPCODE_ONGREEN:
   case OPCODE_ONCHANGE:
   case OPCODE_ONTIME:
+  case OPCODE_ONOVERLOAD:
   
     break;
     
@@ -1194,6 +1208,16 @@ void RMFT2::clockEvent(int16_t clocktime, bool change) {
   }
 } 
 
+void RMFT2::powerEvent(int16_t track, bool overload) {
+  // Hunt for an ONOVERLOAD for this item
+  if (Diag::CMD)
+   DIAG(F("Looking for Power event on track : %c"), track);
+  if (overload) {
+    handleEvent(F("POWER"),onOverloadLookup,track);
+  }
+}
+
+
 void RMFT2::handleEvent(const FSH* reason,LookList* handlers, int16_t id) {
   int pc= handlers->find(id);
   if (pc<0) return;
diff --git a/EXRAIL2.h b/EXRAIL2.h
index 0cc995d..f43d7d4 100644
--- a/EXRAIL2.h
+++ b/EXRAIL2.h
@@ -1,7 +1,7 @@
 /*
  *  © 2021 Neil McKechnie
  *  © 2020-2022 Chris Harlow
- *  © 2022 Colin Murdoch
+ *  © 2022-2023 Colin Murdoch
  *  © 2023 Harald Barth
  *  All rights reserved.
  *  
@@ -35,7 +35,8 @@
 enum OPCODE : byte {OPCODE_THROW,OPCODE_CLOSE,
              OPCODE_FWD,OPCODE_REV,OPCODE_SPEED,OPCODE_INVERT_DIRECTION,
              OPCODE_RESERVE,OPCODE_FREE,
-             OPCODE_AT,OPCODE_AFTER,OPCODE_AUTOSTART,
+             OPCODE_AT,OPCODE_AFTER,
+             OPCODE_AFTEROVERLOAD,OPCODE_AUTOSTART,
              OPCODE_ATGTE,OPCODE_ATLT,
              OPCODE_ATTIMEOUT1,OPCODE_ATTIMEOUT2,
              OPCODE_LATCH,OPCODE_UNLATCH,OPCODE_SET,OPCODE_RESET,
@@ -63,6 +64,7 @@ enum OPCODE : byte {OPCODE_THROW,OPCODE_CLOSE,
              OPCODE_ONCLOCKTIME,
              OPCODE_ONTIME,
              OPCODE_LCC,OPCODE_ONLCC,
+             OPCODE_ONOVERLOAD,
 
              // OPcodes below this point are skip-nesting IF operations
              // placed here so that they may be skipped as a group
@@ -131,6 +133,7 @@ class LookList {
     static void activateEvent(int16_t addr, bool active);
     static void changeEvent(int16_t id, bool change);
     static void clockEvent(int16_t clocktime, bool change);
+    static void powerEvent(int16_t track, bool overload);
     static const int16_t SERVO_SIGNAL_FLAG=0x4000;
     static const int16_t ACTIVE_HIGH_SIGNAL_FLAG=0x2000;
     static const int16_t DCC_SIGNAL_FLAG=0x1000;
@@ -190,6 +193,8 @@ private:
    static LookList * onGreenLookup;
    static LookList * onChangeLookup;
    static LookList * onClockLookup;
+   static LookList * onOverloadLookup;
+   
    static const int countLCCLookup;
    static int onLCCLookup[];
     
diff --git a/EXRAIL2MacroReset.h b/EXRAIL2MacroReset.h
index 9ea1a36..a952d90 100644
--- a/EXRAIL2MacroReset.h
+++ b/EXRAIL2MacroReset.h
@@ -1,6 +1,6 @@
 /*
  *  © 2020-2022 Chris Harlow. All rights reserved.
- *  © 2022 Colin Murdoch
+ *  © 2022-2023 Colin Murdoch
  *  © 2023 Harald Barth
  *  
  *  This file is part of CommandStation-EX
@@ -27,6 +27,7 @@
 #undef ACTIVATE
 #undef ACTIVATEL
 #undef AFTER
+#undef AFTEROVERLOAD
 #undef ALIAS
 #undef AMBER
 #undef ANOUT
@@ -95,6 +96,7 @@
 #undef ONTIME
 #undef ONCLOCKTIME
 #undef ONCLOCKMINS
+#undef ONOVERLOAD
 #undef ONGREEN
 #undef ONRED
 #undef ONTHROW 
@@ -154,6 +156,7 @@
 #define ACTIVATE(addr,subaddr)
 #define ACTIVATEL(addr)
 #define AFTER(sensor_id)
+#define AFTEROVERLOAD(track_id)
 #define ALIAS(name,value...)
 #define AMBER(signal_id)
 #define ANOUT(vpin,value,param1,param2)
@@ -218,6 +221,7 @@
 #define ONTIME(value)
 #define ONCLOCKTIME(hours,mins)
 #define ONCLOCKMINS(mins)
+#define ONOVERLOAD(track_id)
 #define ONDEACTIVATE(addr,subaddr)
 #define ONDEACTIVATEL(linear) 
 #define ONCLOSE(turnout_id)
diff --git a/EXRAILMacros.h b/EXRAILMacros.h
index 18abf7a..0127610 100644
--- a/EXRAILMacros.h
+++ b/EXRAILMacros.h
@@ -1,7 +1,7 @@
 /*
  *  © 2021 Neil McKechnie
  *  © 2020-2022 Chris Harlow
- *  © 2022 Colin Murdoch
+ *  © 2022-2023 Colin Murdoch
  *  © 2023 Harald Barth
  *  All rights reserved.
  *  
@@ -266,6 +266,7 @@ int RMFT2::onLCCLookup[RMFT2::countLCCLookup];
 #define ACTIVATE(addr,subaddr) OPCODE_DCCACTIVATE,V(addr<<3 | subaddr<<1 | 1),
 #define ACTIVATEL(addr) OPCODE_DCCACTIVATE,V((addr+3)<<1 | 1),
 #define AFTER(sensor_id) OPCODE_AT,V(sensor_id),OPCODE_AFTER,V(sensor_id),
+#define AFTEROVERLOAD(track_id) OPCODE_AFTEROVERLOAD,V(TRACK_NUMBER_##track_id),
 #define ALIAS(name,value...) 
 #define AMBER(signal_id) OPCODE_AMBER,V(signal_id),
 #define ANOUT(vpin,value,param1,param2) OPCODE_SERVO,V(vpin),OPCODE_PAD,V(value),OPCODE_PAD,V(param1),OPCODE_PAD,V(param2),
@@ -335,6 +336,7 @@ int RMFT2::onLCCLookup[RMFT2::countLCCLookup];
 #define ONTIME(value) OPCODE_ONTIME,V(value),  
 #define ONCLOCKTIME(hours,mins) OPCODE_ONTIME,V((STRIP_ZERO(hours)*60)+STRIP_ZERO(mins)),
 #define ONCLOCKMINS(mins) ONCLOCKTIME(25,mins)
+#define ONOVERLOAD(track_id) OPCODE_ONOVERLOAD,V(TRACK_NUMBER_##track_id),
 #define ONDEACTIVATE(addr,subaddr) OPCODE_ONDEACTIVATE,V(addr<<2|subaddr),
 #define ONDEACTIVATEL(linear) OPCODE_ONDEACTIVATE,V(linear+3),
 #define ONGREEN(signal_id) OPCODE_ONGREEN,V(signal_id),
diff --git a/GITHUB_SHA.h b/GITHUB_SHA.h
index ae005b5..98afa03 100644
--- a/GITHUB_SHA.h
+++ b/GITHUB_SHA.h
@@ -1 +1 @@
-#define GITHUB_SHA "3bddf4d"
+#define GITHUB_SHA "devel-202308302157Z"
diff --git a/IODevice.h b/IODevice.h
index 769e111..4eb24e5 100644
--- a/IODevice.h
+++ b/IODevice.h
@@ -29,8 +29,13 @@
 
 // Define symbol IO_NO_HAL to reduce FLASH footprint when HAL features not required
 // The HAL is disabled by default on Nano and Uno platforms, because of limited flash space.
-#if defined(ARDUINO_AVR_NANO) || defined(ARDUINO_AVR_UNO) 
-#define IO_NO_HAL
+#include "defines.h"
+#if defined(ARDUINO_AVR_NANO) || defined(ARDUINO_AVR_UNO)
+  #if defined(DISABLE_DIAG) && defined(DISABLE_EEPROM) && defined(DISABLE_PROG)
+    #warning you have sacrificed DIAG for HAL
+  #else
+    #define IO_NO_HAL
+  #endif
 #endif
 
 // Define symbol IO_SWITCH_OFF_SERVO to set the PCA9685 output to 0 when an 
diff --git a/IO_PCA9555.h b/IO_PCA9555.h
index 137e287..e493165 100644
--- a/IO_PCA9555.h
+++ b/IO_PCA9555.h
@@ -30,8 +30,8 @@
  
 class PCA9555 : public GPIOBase<uint16_t> {
 public:
-  static void create(VPIN vpin, int nPins, uint8_t I2CAddress, int interruptPin=-1) {
-    new PCA9555(vpin, min(nPins,16), I2CAddress, interruptPin);
+  static void create(VPIN vpin, uint8_t nPins, I2CAddress i2cAddress, int interruptPin=-1) {
+    if (checkNoOverlap(vpin, nPins, i2cAddress)) new PCA9555(vpin,nPins, i2cAddress, interruptPin);
   }
   
   // Constructor
diff --git a/MotorDriver.cpp b/MotorDriver.cpp
index d5dca13..4644ad5 100644
--- a/MotorDriver.cpp
+++ b/MotorDriver.cpp
@@ -4,6 +4,7 @@
  *  © 2021 Fred Decker
  *  © 2020-2023 Harald Barth
  *  © 2020-2021 Chris Harlow
+ *  © 2023 Colin Murdoch
  *  All rights reserved.
  *  
  *  This file is part of CommandStation-EX
@@ -26,6 +27,7 @@
 #include "DCCWaveform.h"
 #include "DCCTimer.h"
 #include "DIAG.h"
+#include "EXRAIL2.h"
 
 unsigned long MotorDriver::globalOverloadStart = 0;
 
@@ -613,7 +615,9 @@ void MotorDriver::checkPowerOverload(bool useProgLimit, byte trackno) {
       // adjust next wait time
       power_sample_overload_wait *= 2;
       if (power_sample_overload_wait > POWER_SAMPLE_RETRY_MAX)
-	power_sample_overload_wait = POWER_SAMPLE_RETRY_MAX;
+	      power_sample_overload_wait = POWER_SAMPLE_RETRY_MAX;
+      DIAG(F("Calling EXRAIL"));
+      RMFT2::powerEvent(trackno, true); // Tell EXRAIL we have an overload
       // power on test
       DIAG(F("TRACK %c POWER RESTORE (after %4M)"), trackno + 'A', mslpc);
       setPower(POWERMODE::ALERT);
diff --git a/TrackManager.cpp b/TrackManager.cpp
index 0f69235..bd7c623 100644
--- a/TrackManager.cpp
+++ b/TrackManager.cpp
@@ -1,6 +1,7 @@
 /*
  *  © 2022 Chris Harlow
  *  © 2022 Harald Barth
+ *  © 2023 Colin Murdoch
  *  All rights reserved.
  *  
  *  This file is part of DCC++EX
@@ -53,7 +54,7 @@ bool TrackManager::progTrackSyncMain=false;
 bool TrackManager::progTrackBoosted=false; 
 int16_t TrackManager::joinRelay=UNUSED_PIN;
 #ifdef ARDUINO_ARCH_ESP32
-byte TrackManager::tempProgTrack=MAX_TRACKS+1;
+byte TrackManager::tempProgTrack=MAX_TRACKS+1; // MAX_TRACKS+1 is the unused flag
 #endif
 
 #ifdef ANALOG_READ_INTERRUPT
@@ -505,7 +506,12 @@ void TrackManager::setJoin(bool joined) {
     }
   } else {
     if (tempProgTrack != MAX_TRACKS+1) {
+      // as setTrackMode with TRACK_MODE_PROG defaults to
+      // power off, we will take the current power state
+      // of our track and then preserve that state.
+      POWERMODE tPTmode = track[tempProgTrack]->getPower(); //get current power status of this track
       setTrackMode(tempProgTrack, TRACK_MODE_PROG);
+      track[tempProgTrack]->setPower(tPTmode);              //set track status as it was before
       tempProgTrack = MAX_TRACKS+1;
     }
   }
@@ -513,3 +519,10 @@ void TrackManager::setJoin(bool joined) {
   progTrackSyncMain=joined;
   if (joinRelay!=UNUSED_PIN) digitalWrite(joinRelay,joined?HIGH:LOW);
 }
+
+bool TrackManager::isPowerOn(byte t) {
+      if (track[t]->getPower()!=POWERMODE::ON) 
+	        return false;
+    return true;   
+  }
+
diff --git a/TrackManager.h b/TrackManager.h
index 965cfa3..60d5f24 100644
--- a/TrackManager.h
+++ b/TrackManager.h
@@ -1,6 +1,8 @@
 /*
  *  © 2022 Chris Harlow
  *  © 2022 Harald Barth
+ *  © 2023 Colin Murdoch
+ * 
  *  All rights reserved.
  *  
  *  This file is part of CommandStation-EX
@@ -77,6 +79,7 @@ class TrackManager {
     static void reportCurrent(Print* stream);
     static void reportObsoleteCurrent(Print* stream); 
     static void streamTrackState(Print* stream, byte t);
+    static bool isPowerOn(byte t);
 
     static int16_t joinRelay;
     static bool progTrackSyncMain;  // true when prog track is a siding switched to main
diff --git a/WifiInterface.cpp b/WifiInterface.cpp
index 7511af6..ab36957 100644
--- a/WifiInterface.cpp
+++ b/WifiInterface.cpp
@@ -200,7 +200,21 @@ wifiSerialState WifiInterface::setup2(const FSH* SSid, const FSH* password,
 
   // Display the AT version information
   StringFormatter::send(wifiStream, F("AT+GMR\r\n")); 
-  checkForOK(2000, true, false);      // Makes this visible on the console
+  if (checkForOK(2000, F("AT version:"), true, false)) {
+    char version[] = "0.0.0.0";
+    for (int i=0; i<8;i++) {
+      while(!wifiStream->available());
+      version[i]=wifiStream->read();
+      StringFormatter::printEscape(version[i]);
+      if ((version[0] == '0') ||
+	  (version[0] == '2' && version[2] == '0') ||
+	  (version[0] == '2' && version[2] == '2' && version[4] == '0' && version[6] == '0')) {
+	SSid = F("DCCEX_SAYS_BROKEN_FIRMWARE");
+	forceAP = true;
+      }
+    }
+  }
+  checkForOK(2000, true, false);
 
 #ifdef DONT_TOUCH_WIFI_CONF
   DIAG(F("DONT_TOUCH_WIFI_CONF was set: Using existing config"));
diff --git a/myHal.cpp_example.txt b/myHal.cpp_example.txt
index d93ea5c..5e9fec4 100644
--- a/myHal.cpp_example.txt
+++ b/myHal.cpp_example.txt
@@ -51,7 +51,7 @@ void halSetup() {
   // Create a 20x4 LCD display device as display number 2 
   // (line 0 is written by EX-RAIL 'SCREEN(2, 0, "text")').
 
-  // HALDisplay<LiquidCrystal>(2, 0x27, 20, 4);
+  // HALDisplay<LiquidCrystal>::create(2, 0x27, 20, 4);
 
 
   //=======================================================================
diff --git a/version.h b/version.h
index 449b18e..881e992 100644
--- a/version.h
+++ b/version.h
@@ -3,7 +3,7 @@
 
 #include "StringFormatter.h"
 
-#define VERSION "5.0.1LCC"
+#define VERSION "5.1.5LCC"
 // 5.0.0  - Make 4.2.69 the 5.0.0 release
 // 4.2.69 - Bugfix: Make <!> work in DC mode
 // 4.2.68 - Rename track mode OFF to NONE