Make sure _Ex_PINS is defined

Also fix analogInputToDigitalPin so it uses proper C hex notation

Marlin/Marlin.h

 
 // Arduino < 1.0.0 does not define this, so we need to do it ourselves
 #ifndef analogInputToDigitalPin
-# define analogInputToDigitalPin(p) ((p) + A0)
+# define analogInputToDigitalPin(p) ((p) + 0xA0)
 #endif
 
 #ifdef AT90USB

Marlin/pins.h

 
 // List of pins which to ignore when asked to change by gcode, 0 and 1 are RX and TX, do not mess with those!
 #define _E0_PINS E0_STEP_PIN, E0_DIR_PIN, E0_ENABLE_PIN, HEATER_0_PIN, analogInputToDigitalPin(TEMP_0_PIN),
+#define _E1_PINS
+#define _E2_PINS
+#define _E3_PINS
+
 #if EXTRUDERS > 1
   #define _E1_PINS E1_STEP_PIN, E1_DIR_PIN, E1_ENABLE_PIN, HEATER_1_PIN, analogInputToDigitalPin(TEMP_1_PIN),
   #if EXTRUDERS > 2
     #define _E2_PINS E2_STEP_PIN, E2_DIR_PIN, E2_ENABLE_PIN, HEATER_2_PIN, analogInputToDigitalPin(TEMP_2_PIN),
     #if EXTRUDERS > 3
       #define _E3_PINS E3_STEP_PIN, E3_DIR_PIN, E3_ENABLE_PIN, HEATER_3_PIN, analogInputToDigitalPin(TEMP_3_PIN),
-    #else
-      #define _E3_PINS
     #endif
-  #else
-    #define _E2_PINS
   #endif
-#else
-  #define _E1_PINS
 #endif
 
 #ifdef X_STOP_PIN

Marlin/pins_MEGATRONICS_3.h

+/**
+ * MegaTronics v2.0 pin assignments
+ */
+
+#ifndef __AVR_ATmega2560__
+  #error Oops!  Make sure you have 'Arduino Mega' selected from the 'Tools -> Boards' menu.
+#endif
+
+#define LARGE_FLASH        true
+
+#define X_STEP_PIN 26
+#define X_DIR_PIN 27
+#define X_ENABLE_PIN 25
+#define X_MIN_PIN 37
+#define X_MAX_PIN 40
+
+#define Y_STEP_PIN 4 // A6
+#define Y_DIR_PIN 54 // A0
+#define Y_ENABLE_PIN 5
+#define Y_MIN_PIN 41
+#define Y_MAX_PIN 38
+
+#define Z_STEP_PIN 56 // A2
+#define Z_DIR_PIN 60 // A6
+#define Z_ENABLE_PIN 55 // A1
+#define Z_MIN_PIN 18
+#define Z_MAX_PIN 19
+
+#define E0_STEP_PIN 35
+#define E0_DIR_PIN 36
+#define E0_ENABLE_PIN 34
+
+#define E1_STEP_PIN 29
+#define E1_DIR_PIN 39
+#define E1_ENABLE_PIN 28
+
+#define E2_STEP_PIN 23
+#define E2_DIR_PIN 24
+#define E2_ENABLE_PIN 22
+
+#define SDPOWER -1
+#define SDSS 53
+#define LED_PIN 13
+
+#define FAN_PIN 7
+#define FAN2_PIN 6
+#define PS_ON_PIN 12
+#define KILL_PIN -1
+
+#define HEATER_0_PIN 9 // EXTRUDER 1
+#define HEATER_1_PIN 8 // EXTRUDER 2
+#define HEATER_2_PIN -1
+
+#if TEMP_SENSOR_0 == -1
+  #define TEMP_0_PIN 4 // ANALOG NUMBERING
+#else
+  #define TEMP_0_PIN 13 // ANALOG NUMBERING
+#endif
+
+
+#if TEMP_SENSOR_1 == -1
+  #define TEMP_1_PIN 8 // ANALOG NUMBERING
+#else
+  #define TEMP_1_PIN 15 // ANALOG NUMBERING
+#endif
+
+#define TEMP_2_PIN -1 // ANALOG NUMBERING
+
+#define HEATER_BED_PIN 10 // BED
+
+#if TEMP_SENSOR_BED == -1
+  #define TEMP_BED_PIN 8 // ANALOG NUMBERING
+#else
+  #define TEMP_BED_PIN 14 // ANALOG NUMBERING
+#endif
+
+#define BEEPER 64
+
+
+#define LCD_PINS_RS 14
+#define LCD_PINS_ENABLE 15
+#define LCD_PINS_D4 30
+#define LCD_PINS_D5 31
+#define LCD_PINS_D6 32
+#define LCD_PINS_D7 33
+
+
+// Buttons are directly attached using keypad
+#define BTN_EN1 61
+#define BTN_EN2 59
+#define BTN_ENC 43 //the click
+
+#define BLEN_C 2
+#define BLEN_B 1
+#define BLEN_A 0
+
+#define SDCARDDETECT -1  // Megatronics does not use this port
+
+// Encoder rotation values
+#define encrot0 0
+#define encrot1 2
+#define encrot2 3
+#define encrot3 1