diff --git a/DCC.cpp b/DCC.cpp
index 972dfa3..96868ca 100644
--- a/DCC.cpp
+++ b/DCC.cpp
@@ -465,15 +465,15 @@ bool DCC::issueReminder(int reg) {
          break;
        case 1: // remind function group 1 (F0-F4)
           if (flags & FN_GROUP_1) 
-              setFunctionInternal(loco,0, 128 | ((functions>>1)& 0x0F) | ((functions & 0x01)<<4));   
+              setFunctionInternal(loco,0, 128 | ((functions>>1)& 0x0F) | ((functions & 0x01)<<4)); // 100D DDDD
           break;     
        case 2: // remind function group 2 F5-F8
           if (flags & FN_GROUP_2) 
-              setFunctionInternal(loco,0, 176 + ((functions>>5)& 0x0F));   
+              setFunctionInternal(loco,0, 176 | ((functions>>5)& 0x0F));                           // 1011 DDDD
           break;     
        case 3: // remind function group 3 F9-F12
           if (flags & FN_GROUP_3) 
-              setFunctionInternal(loco,0, 160 + ((functions>>9)& 0x0F));
+              setFunctionInternal(loco,0, 160 | ((functions>>9)& 0x0F));                           // 1010 DDDD
           break;   
        case 4: // remind function group 4 F13-F20
           if (flags & FN_GROUP_4) 
diff --git a/DCCEXParser.cpp b/DCCEXParser.cpp
index 4f4030c..ece2842 100644
--- a/DCCEXParser.cpp
+++ b/DCCEXParser.cpp
@@ -47,6 +47,7 @@ const int HASH_KEYWORD_DCC = 6436;
 const int HASH_KEYWORD_SLOW = -17209;
 const int HASH_KEYWORD_PROGBOOST = -6353;
 const int HASH_KEYWORD_EEPROM = -7168;
+const int HASH_KEYWORD_LIMIT = 27413;
 
 int DCCEXParser::stashP[MAX_PARAMS];
 bool DCCEXParser::stashBusy;
@@ -465,19 +466,19 @@ bool DCCEXParser::parsef(Print *stream, int params, int p[])
     //      convenient for other processing
     if (params == 2)
     {
-        byte groupcode = p[1] & 0xE0;
-        if (groupcode == 0x80)
+        byte instructionField = p[1] & 0xE0;   // 1110 0000
+        if (instructionField == 0x80)          // 1000 0000 Function group 1
         {
+	    // Shuffle bits from order F0 F4 F3 F2 F1 to F4 F3 F2 F1 F0 
             byte normalized = (p[1] << 1 & 0x1e) | (p[1] >> 4 & 0x01);
             funcmap(p[0], normalized, 0, 4);
         }
-        else if (groupcode == 0xC0)
+        else if (instructionField == 0xA0)     // 1010 0000 Function group 2
         {
-            funcmap(p[0], p[1], 5, 8);
-        }
-        else if (groupcode == 0xA0)
-        {
-            funcmap(p[0], p[1], 9, 12);
+	    if (p[1] & 0x10)                   // 0001 0000 Bit selects F5toF8 / F9toF12
+		funcmap(p[0], p[1], 5, 8);
+	    else
+		funcmap(p[0], p[1], 9, 12);
         }
     }
     if (params == 3)
@@ -586,7 +587,11 @@ bool DCCEXParser::parseD(Print *stream, int params, int p[])
         break;
 
     case HASH_KEYWORD_ACK: // <D ACK ON/OFF>
-        Diag::ACK = onOff;
+	if (params >= 2 && p[1] == HASH_KEYWORD_LIMIT) {
+	  DCCWaveform::progTrack.setAckLimit(p[2]);
+          StringFormatter::send(stream, F("\nAck limit=%dmA\n"), p[2]);
+	} else
+	  Diag::ACK = onOff;
         return true;
 
     case HASH_KEYWORD_CMD: // <D CMD ON/OFF>
diff --git a/DCCWaveform.cpp b/DCCWaveform.cpp
index a70ab16..bec16b3 100644
--- a/DCCWaveform.cpp
+++ b/DCCWaveform.cpp
@@ -128,7 +128,7 @@ void DCCWaveform::checkPowerOverload() {
 
   if (millis() - lastSampleTaken  < sampleDelay) return;
   lastSampleTaken = millis();
-  int tripValue= motorDriver->rawCurrentTripValue;
+  int tripValue= motorDriver->getRawCurrentTripValue();
   if (!isMainTrack && !ackPending && !progTrackSyncMain && !progTrackBoosted)
     tripValue=progTripValue;
   
@@ -292,9 +292,12 @@ int DCCWaveform::getLastCurrent() {
 // (yes I know I could have subclassed the main track but...) 
 
 void DCCWaveform::setAckBaseline() {
-      if (isMainTrack) return; 
-      ackThreshold=motorDriver->getCurrentRaw() + (int)(65 / motorDriver->senseFactor);
-      if (Diag::ACK) DIAG(F("\nACK-BASELINE %d/%dmA"),ackThreshold,motorDriver->raw2mA(ackThreshold));
+      if (isMainTrack) return;
+      int baseline = motorDriver->getCurrentRaw();
+      ackThreshold= baseline + motorDriver->mA2raw(ackLimitmA);
+      if (Diag::ACK) DIAG(F("\nACK baseline=%d/%dmA threshold=%d/%dmA"),
+			  baseline,motorDriver->raw2mA(baseline),
+			  ackThreshold,motorDriver->raw2mA(ackThreshold));
 }
 
 void DCCWaveform::setAckPending() {
diff --git a/DCCWaveform.h b/DCCWaveform.h
index d607420..32041e6 100644
--- a/DCCWaveform.h
+++ b/DCCWaveform.h
@@ -76,6 +76,9 @@ class DCCWaveform {
 	    autoPowerOff=false;
 	}
     };
+    inline void setAckLimit(int mA) {
+	ackLimitmA = mA;
+    }
      
   private:
     static VirtualTimer * interruptTimer;      
@@ -115,9 +118,10 @@ class DCCWaveform {
     unsigned int power_good_counter = 0;
 
     // ACK management (Prog track only)  
-    bool ackPending;    
-    bool ackDetected;   
+    volatile bool ackPending;
+    volatile bool ackDetected;
     int  ackThreshold; 
+    int  ackLimitmA = 60;
     int ackMaxCurrent;
     unsigned long ackCheckStart; // millis
     unsigned int ackCheckDuration; // millis       
diff --git a/MotorDriver.h b/MotorDriver.h
index cce07ad..cbc09cc 100644
--- a/MotorDriver.h
+++ b/MotorDriver.h
@@ -29,12 +29,16 @@ class MotorDriver {
     virtual int  getCurrentRaw();
     virtual unsigned int raw2mA( int raw);
     virtual int mA2raw( unsigned int mA);
-  
+    inline int getRawCurrentTripValue() {
+	return rawCurrentTripValue;
+    }
+
+  private:
     byte powerPin, signalPin, signalPin2, brakePin,currentPin,faultPin;
-   float senseFactor;
-   unsigned int tripMilliamps;
-   int rawCurrentTripValue;
-   const byte UNUSED_PIN = 255;
+    float senseFactor;
+    unsigned int tripMilliamps;
+    int rawCurrentTripValue;
+    const byte UNUSED_PIN = 255;
     
 };
 #endif