diff --git a/MotorDriver.cpp b/MotorDriver.cpp
index 701816a..a77c2d2 100644
--- a/MotorDriver.cpp
+++ b/MotorDriver.cpp
@@ -41,16 +41,20 @@ MotorDriver::MotorDriver(VPIN power_pin, byte signal_pin, byte signal_pin2, int8
   getFastPin(F("SIG"),signalPin,fastSignalPin);
   pinMode(signalPin, OUTPUT);
 
+  fastSignalPin.shadowinout = NULL;
   if (HAVE_PORTA(fastSignalPin.inout == &PORTA)) {
     DIAG(F("Found PORTA pin %d"),signalPin);
+    fastSignalPin.shadowinout = fastSignalPin.inout;
     fastSignalPin.inout = &fakePORTA;
   }
   if (HAVE_PORTB(fastSignalPin.inout == &PORTB)) {
     DIAG(F("Found PORTB pin %d"),signalPin);
+    fastSignalPin.shadowinout = fastSignalPin.inout;
     fastSignalPin.inout = &fakePORTB;
   }
   if (HAVE_PORTC(fastSignalPin.inout == &PORTC)) {
     DIAG(F("Found PORTC pin %d"),signalPin);
+    fastSignalPin.shadowinout = fastSignalPin.inout;
     fastSignalPin.inout = &fakePORTC;
   }
 
@@ -162,15 +166,39 @@ int MotorDriver::getCurrentRaw() {
 void MotorDriver::setDCSignal(byte speedcode) {
   if (brakePin == UNUSED_PIN)
     return;
-  // spedcoode is a dcc speed /direction
-  byte tSpeed=speedcode & 0x7F;
-    // DCC Speed with 0,1 stop and speed steps 2 to 127
+  // spedcoode is a dcc speed & direction
+  byte tSpeed=speedcode & 0x7F; // DCC Speed with 0,1 stop and speed steps 2 to 127
+  byte tDir=speedcode & 0x80;
   byte brake;
   if (tSpeed <= 1) brake = 255;
   else if (tSpeed >= 127) brake = 0;
   else  brake = 2 * (128-tSpeed);
   analogWrite(brakePin,brake);
-  setSignal(speedcode & 0x80);  
+  // as the port registers can be shadowed to get syncronized DCC signals
+  // we need to take care of that and we have to turn off interrupts during
+  // that time as otherwise setDCCSignal() which is called from interrupt
+  // contect can undo whatever we do here.
+  if (fastSignalPin.shadowinout != NULL) {
+    if (HAVE_PORTA(fastSignalPin.shadowinout == &PORTA)) {
+      noInterrupts();
+      fakePORTA=PORTA;
+      setSignal(tDir);
+      PORTA=fakePORTA;
+      interrupts();
+    } else if (HAVE_PORTB(fastSignalPin.shadowinout == &PORTB)) {
+      noInterrupts();
+      fakePORTB=PORTB;
+      setSignal(tDir);
+      PORTB=fakePORTB;
+      interrupts();
+    } else if (HAVE_PORTC(fastSignalPin.shadowinout == &PORTC)) {
+      noInterrupts();
+      fakePORTC=PORTC;
+      setSignal(tDir);
+      PORTC=fakePORTC;
+      interrupts();
+    }
+  }
 }
 
 int MotorDriver::getCurrentRawInInterrupt() {
diff --git a/MotorDriver.h b/MotorDriver.h
index 4c7d6ff..7f0b169 100644
--- a/MotorDriver.h
+++ b/MotorDriver.h
@@ -65,13 +65,15 @@
 struct FASTPIN {
   volatile uint32_t *inout;
   uint32_t maskHIGH;  
-  uint32_t maskLOW;  
+  uint32_t maskLOW;
+  volatile uint32_t *shadowinout;
 };
 #else
 struct FASTPIN {
   volatile uint8_t *inout;
   uint8_t maskHIGH;  
-  uint8_t maskLOW;  
+  uint8_t maskLOW;
+  volatile uint8_t *shadowinout;
 };
 #endif
 
diff --git a/TrackManager.cpp b/TrackManager.cpp
index 87ea735..4727dc8 100644
--- a/TrackManager.cpp
+++ b/TrackManager.cpp
@@ -87,11 +87,15 @@ void TrackManager::addTrack(byte t, MotorDriver* driver) {
      } 
 }
 
+// The port registers that are shadowing
+// the real port registers. These are
 // defined in Motordriver.cpp
 extern byte fakePORTA;
 extern byte fakePORTB;
 extern byte fakePORTC;
 
+// setDCCSignal(), called from interrupt context
+// does assume ports are shadowed if they can be
 void TrackManager::setDCCSignal( bool on) {
   HAVE_PORTA(fakePORTA=PORTA);
   HAVE_PORTB(fakePORTB=PORTB);
@@ -108,6 +112,8 @@ void TrackManager::setCutout( bool on) {
     // TODO      APPLY_BY_MODE(TRACK_MODE_MAIN,setCutout(on));
 }
 
+// setPROGSignal(), called from interrupt context
+// does assume ports are shadowed if they can be
 void TrackManager::setPROGSignal( bool on) {
   HAVE_PORTA(fakePORTA=PORTA);
   HAVE_PORTB(fakePORTB=PORTB);
@@ -118,18 +124,15 @@ void TrackManager::setPROGSignal( bool on) {
   HAVE_PORTC(PORTC=fakePORTC);
 }
 
+// setDCSignal(), called from normal context
+// MotorDriver::setDCSignal handles shadowed IO port changes.
+// with interrupts turned off around the critical section
 void TrackManager::setDCSignal(int16_t cab, byte speedbyte) {
-  HAVE_PORTA(fakePORTA=PORTA);
-  HAVE_PORTB(fakePORTB=PORTB);
-  HAVE_PORTC(fakePORTC=PORTC);
   FOR_EACH_TRACK(t) {
     if (trackDCAddr[t]!=cab) continue;
     if (trackMode[t]==TRACK_MODE_DC) track[t]->setDCSignal(speedbyte);
     else if (trackMode[t]==TRACK_MODE_DCX) track[t]->setDCSignal(speedbyte ^ 128);
   }
-  HAVE_PORTA(PORTA=fakePORTA);
-  HAVE_PORTB(PORTB=fakePORTB);
-  HAVE_PORTC(PORTC=fakePORTC);
 }    
 
 
@@ -193,10 +196,11 @@ bool TrackManager::setTrackMode(byte trackToSet, TRACK_MODE mode, int16_t dcAddr
       } else if (trackMode[t]==TRACK_MODE_MAIN || trackMode[t]==TRACK_MODE_PROG)
 	canDo &= track[t]->isPWMCapable();
     }
-    //DIAG(F("HAMode=%d"),canDo);
     if (!canDo) {
       DCCTimer::clearPWM();
     }
+    //if (MotorDriver::usePWM != canDo)
+    //  DIAG(F("HA mode changed from %d to %d"), MotorDriver::usePWM, canDo);
     MotorDriver::usePWM=canDo;
 
     
@@ -211,7 +215,7 @@ bool TrackManager::setTrackMode(byte trackToSet, TRACK_MODE mode, int16_t dcAddr
 void TrackManager::applyDCSpeed(byte t) {
   uint8_t speedByte=DCC::getThrottleSpeedByte(trackDCAddr[t]);
   if (trackMode[t]==TRACK_MODE_DCX)
-    speedByte = (speedByte & 0xF7) | ~(speedByte & 0x80); // Reverse highest bit
+    speedByte = speedByte ^ 128; // reverse direction bit
   track[t]->setDCSignal(speedByte);
 }