diff --git a/Repetier/Configuration.h b/Repetier/Configuration.h
index 1a48a7976..7cf04eb4d 100644
--- a/Repetier/Configuration.h
+++ b/Repetier/Configuration.h
@@ -946,5 +946,8 @@ and it is elsewise difficult to know, what your reprap is currently doing. */
 /** \brief Defines the default z scale */
 #define DEFAULT_Z_SCALE_MODE                Z_VALUE_MODE_Z_MIN
 
+/** \brief For Nibbels external interrupt 3 button at RF1000 X25.8 und RF2000 X34.2 "EXT_IRQ"/INT3 
+You can activate this to 1 and connect some Button. If you connect ground to pull the pullup down you will let the firmware jump into interrupt routine */
+#define FEATURE_USER_INT3                   0                                                   // 0 = OFF, 1 = ON
 
 #endif // CONFIGURATION_H
diff --git a/Repetier/HAL.cpp b/Repetier/HAL.cpp
index 3bfc78bfe..ffb15596e 100644
--- a/Repetier/HAL.cpp
+++ b/Repetier/HAL.cpp
@@ -1207,6 +1207,14 @@ ISR(EXTRUDER_TIMER_VECTOR)
 }
 #endif // USE_ADVANCE
 
+#if FEATURE_USER_INT3
+volatile unsigned long g_uCOUNT_INT3 = 0; //dummy variable for dummy function!
+
+void USER_INTERRUPT3_HOOK(){
+    g_uCOUNT_INT3++; //dummy function!
+}
+#endif //FEATURE_USER_INT3
+
 #ifndef EXTERNALSERIAL
 // Implement serial communication for one stream only!
 /*
diff --git a/Repetier/HAL.h b/Repetier/HAL.h
index 3d3c2e2e6..b5cbadbd7 100644
--- a/Repetier/HAL.h
+++ b/Repetier/HAL.h
@@ -122,6 +122,12 @@ typedef uint8_t     flag8_t;
 
 #define FAST_INTEGER_SQRT
 
+#if FEATURE_USER_INT3
+extern volatile unsigned long g_uCOUNT_INT3; //dummy variable for dummy function!
+
+void USER_INTERRUPT3_HOOK(); //dummy function!
+#endif //FEATURE_USER_INT3
+
 #ifndef EXTERNALSERIAL
 // Implement serial communication for one stream only!
 /*
@@ -204,7 +210,7 @@ class RFHardwareSerial : public Print
 extern RFHardwareSerial RFSerial;
 #define RFSERIAL RFSerial
 #define WAIT_OUT_EMPTY while(tx_buffer.head != tx_buffer.tail) {}
-#else
+#else // EXTERNALSERIAL
 #define RFSERIAL Serial
 #endif // EXTERNALSERIAL
 
diff --git a/Repetier/Printer.cpp b/Repetier/Printer.cpp
index 0b7328795..0224636dc 100644
--- a/Repetier/Printer.cpp
+++ b/Repetier/Printer.cpp
@@ -898,6 +898,12 @@ void Printer::setup()
 #endif // Z_MAX_PIN>-1
 #endif // MAX_HARDWARE_ENDSTOP_Z
 
+#if FEATURE_USER_INT3
+    SET_INPUT( RESERVE_DIGITAL_PIN_PD3 );
+    PULLUP( RESERVE_DIGITAL_PIN_PD3, HIGH );
+    attachInterrupt( digitalPinToInterrupt(RESERVE_DIGITAL_PIN_PD3) , USER_INTERRUPT3_HOOK, FALLING );
+#endif //FEATURE_USER_INT3
+
 #if FAN_PIN>-1
     SET_OUTPUT(FAN_PIN);
     WRITE(FAN_PIN,LOW);
diff --git a/Repetier/RF.cpp b/Repetier/RF.cpp
index 32a124112..bbfc255ca 100644
--- a/Repetier/RF.cpp
+++ b/Repetier/RF.cpp
@@ -10698,6 +10698,13 @@ void processCommand( GCode* pCommand )
                 break;
             }
 
+#if FEATURE_USER_INT3
+            case 3989: // M3989 : proof that dummy function/additional hardware button works!
+            {
+                Com::printFLN( PSTR( "Request INT3:" ), g_uCOUNT_INT3 ); //evtl. je nach Anwendung entprellen nötig: wenn entprellen nötig, hilft evtl. interrupt nach ausführung sperren und mit dem watchdog-timer erneut entsperren.
+                break;
+            }
+#endif //FEATURE_USER_INT3
         }
     }
 
diff --git a/Repetier/pins.h b/Repetier/pins.h
index 387044531..bc7d83329 100644
--- a/Repetier/pins.h
+++ b/Repetier/pins.h
@@ -253,15 +253,15 @@
 #define FET3                    -1  
 
 //http://www.rf1000.de/viewtopic.php?f=24&t=1119 : 
-#define RESERVE_DIGITAL_PIN_PJ0 15 //RF1000 X25.12 und RF2000 X33.3
-#define RESERVE_DIGITAL_PIN_PJ1 14 //RF1000 X25.13 und RF2000 X33.4
+#define RESERVE_DIGITAL_PIN_PJ0 15 //RF1000 X25.12 und RF2000 X33.3 //Serial3 RX3
+#define RESERVE_DIGITAL_PIN_PJ1 14 //RF1000 X25.13 und RF2000 X33.4 //Serial3 TX3
 
 #define RESERVE_DIGITAL_PIN_PC2 35 //X25.4 
 #define RESERVE_DIGITAL_PIN_PC4 33 //X25.5
 #define RESERVE_DIGITAL_PIN_PC5 32 //X25.6
 
 #define RESERVE_DIGITAL_PIN_PD2 19 //X25.7
-#define RESERVE_DIGITAL_PIN_PD3 18 //RF1000 X25.8 und RF2000 X34.2 "EXT_IRQ"
+#define RESERVE_DIGITAL_PIN_PD3 18 //RF1000 X25.8 und RF2000 X34.2 "EXT_IRQ"/INT3 -> FEATURE_USER_INT3
 
 #define RESERVE_ANALOG_PIN_PF3 3 //X25.10
 #define RESERVE_ANALOG_PIN_PF4 4 //X25.11
@@ -502,12 +502,12 @@
 #define UI_DISPLAY_D7_PIN       98  
 // PINJ.3, 66, D_D7
 
-#define RESERVE_DIGITAL_PIN_PJ0 15 //RF1000 X25.12 und RF2000 X33.3
-#define RESERVE_DIGITAL_PIN_PJ1 14 //RF1000 X25.13 und RF2000 X33.4
+#define RESERVE_DIGITAL_PIN_PJ0 15 //RF1000 X25.12 und RF2000 X33.3 //Serial3 RX3
+#define RESERVE_DIGITAL_PIN_PJ1 14 //RF1000 X25.13 und RF2000 X33.4 //Serial3 TX3
 
 #define RESERVE_DIGITAL_PIN_PE4 2 //RF2000 X33.5
 
-#define RESERVE_DIGITAL_PIN_PD3 18 //RF1000 X25.8 und RF2000 X34.2 "EXT_IRQ"
+#define RESERVE_DIGITAL_PIN_PD3 18 //RF1000 X25.8 und RF2000 X34.2 "EXT_IRQ"/INT3 -> FEATURE_USER_INT3
 /* X34.3=SCL und X34.4=SDA ist I²C siehe wire.h. (X34.1=5V und X34.5/X34.6=VSS) An diesem Bus sind auch die DMS und EEPROMs für Geräteidentifikation (EEPROM 2) und das EEPROM für die Z-Matrix (EEPROM 1) angeschlossen. */
 #endif // MOTHERBOARD == DEVICE_TYPE_RF2000