diff --git a/coolant_control.c b/coolant_control.c
index b866aef..90cde68 100644
--- a/coolant_control.c
+++ b/coolant_control.c
@@ -39,10 +39,17 @@ void coolant_init()
 
 void coolant_stop()
 {
+#ifdef INVERT_COOLANT
   #ifdef ENABLE_M7
-    COOLANT_MIST_PORT &= ~(1 << COOLANT_MIST_BIT);
-  #endif
-  COOLANT_FLOOD_PORT &= ~(1 << COOLANT_FLOOD_BIT);
+    COOLANT_MIST_PORT |= (1 << COOLANT_MIST_BIT);
+   #endif
+  COOLANT_FLOOD_PORT |= (1 << COOLANT_FLOOD_BIT);
+#else
+#ifdef ENABLE_M7
+  COOLANT_MIST_PORT &= ~(1 << COOLANT_MIST_BIT);
+#endif
+   COOLANT_FLOOD_PORT &= ~(1 << COOLANT_FLOOD_BIT);
+#endif
 }
 
 
@@ -51,11 +58,19 @@ void coolant_run(uint8_t mode)
   if (mode != current_coolant_mode)
   { 
     plan_synchronize(); // Ensure coolant turns on when specified in program.
-    if (mode == COOLANT_FLOOD_ENABLE) { 
-      COOLANT_FLOOD_PORT |= (1 << COOLANT_FLOOD_BIT);
+    if (mode == COOLANT_FLOOD_ENABLE) {
+#ifdef INVERT_COOLANT
+    COOLANT_FLOOD_PORT &= ~(1 << COOLANT_FLOOD_BIT);	
+#else
+    COOLANT_FLOOD_PORT |= (1 << COOLANT_FLOOD_BIT);
+#endif
     #ifdef ENABLE_M7  
       } else if (mode == COOLANT_MIST_ENABLE) {
+#ifdef INVERT_COOLANT
+    	  COOLANT_MIST_PORT &= ~(1 << COOLANT_MIST_BIT);
+#else
           COOLANT_MIST_PORT |= (1 << COOLANT_MIST_BIT);
+#endif
     #endif
     } else {
       coolant_stop();
diff --git a/cpu_map.h b/cpu_map.h
index ed97275..70a3984 100644
--- a/cpu_map.h
+++ b/cpu_map.h
@@ -34,6 +34,9 @@
   #define SERIAL_RX     USART_RX_vect
   #define SERIAL_UDRE   USART_UDRE_vect
 
+  // Start of PWM & Stepper Enabled Spindle
+  // #define VARIABLE_SPINDLE // comment this out to disable PWM & Stepper on the spindle
+
   // NOTE: All step bit and direction pins must be on the same port.
   #define STEPPING_DDR       DDRD
   #define STEPPING_PORT      PORTD
@@ -54,6 +57,20 @@
   #define STEPPERS_DISABLE_BIT    0  // Uno Digital Pin 8
   #define STEPPERS_DISABLE_MASK (1<<STEPPERS_DISABLE_BIT)
 
+  #ifdef VARIABLE_SPINDLE // Z LImit has been disabled to make room for the Spindle PWM
+  // NOTE: All limit bit pins must be on the same port
+  #define LIMIT_DDR			DDRB
+  #define LIMIT_PIN			PINB
+  #define LIMIT_PORT		PORTB
+  #define X_LIMIT_BIT		1 // Uno Digital Pin 9
+  #define Y_LIMIT_BIT		2 // Uno Digital Pin 9
+  #define Z_LIMIT_BIT		2 // Uno Digital Pin 11
+  #define LIMIT_INT			PCIE0 // Pin change interrupt enable pin
+  #define LIMIT_INT_vect	PCINT0_vect
+  #define LIMIT_PCMSK		PCMSK0 // Pin change interrupt register
+  #define LIMIT_MASK		((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)) // All limit bits
+
+  #else
   // NOTE: All limit bit pins must be on the same port
   #define LIMIT_DDR       DDRB
   #define LIMIT_PIN       PINB
@@ -65,6 +82,12 @@
   #define LIMIT_INT_vect  PCINT0_vect 
   #define LIMIT_PCMSK     PCMSK0 // Pin change interrupt register
   #define LIMIT_MASK ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)) // All limit bits
+  #endif
+
+  // WARNING if INVERT_SPINDLE is defined the pin will be LOW(Active) on reset of controller until spindle_init() is called.
+  // this should only be a very short period of time but will energise the spindle.
+  // #define INVERT_SPINDLE // This will INVERT the Spindle LOW=Active
+  // END WARNING
 
   #define SPINDLE_ENABLE_DDR   DDRB
   #define SPINDLE_ENABLE_PORT  PORTB
@@ -74,6 +97,11 @@
   #define SPINDLE_DIRECTION_PORT  PORTB
   #define SPINDLE_DIRECTION_BIT   5  // Uno Digital Pin 13 (NOTE: D13 can't be pulled-high input due to LED.)
 
+  // WARNING if INVERT_COOLANT is defined the pin will be LOW(Active) on reset of controller until coolant_init() is called.
+  // this should only be a very short period of time but will energise the coolant pump.
+  // #define INVERT_COOLANT // This will INVERT the Coolant LOW=Active
+  // END WARNING
+
   #define COOLANT_FLOOD_DDR   DDRC
   #define COOLANT_FLOOD_PORT  PORTC
   #define COOLANT_FLOOD_BIT   3  // Uno Analog Pin 3
@@ -99,20 +127,46 @@
   #define PINOUT_PCMSK     PCMSK1 // Pin change interrupt register
   #define PINOUT_MASK ((1<<PIN_RESET)|(1<<PIN_FEED_HOLD)|(1<<PIN_CYCLE_START))
   
-#endif
+  #ifdef VARIABLE_SPINDLE
+
+  #define SPINDLE_IS_PWM // Uncomment this if your Spindle uses PWM ie. DC Motor
+
+    #ifdef SPINDLE_IS_PWM
+      #define SPINDLE_MAX_RPM 255 // Max RPM of your spindle - This value is equal to 100% Duty Cycle on the PWM
+    #endif
+
+  // Advanced Configuration Below You should not need to touch these variables
+
+  //Set Timer up to use TIMER4 OCR4B which is attached to Digital Pin 7
+  #define TCCRA_REGISTER	TCCR2A
+  #define TCCRB_REGISTER	TCCR2B
+  #define OCR_REGISTER		OCR2A
+
+  #define COMB_BIT			COM2A1
+  #define WAVE0_REGISTER	WGM20
+  #define WAVE1_REGISTER	WGM21
+  #define WAVE2_REGISTER	WGM22
+  #define WAVE3_REGISTER	WGM23
+
+  #define SPINDLE_PWM_DDR	DDRB
+  #define SPINDLE_PWM_PORT	PORTB
+  #define SPINDLE_PWM_BIT	3 // UNO Digital Pin 11
+
+  #endif // End of VARIABLE_SPINDLE
+  #endif
 
 
-#ifdef CPU_MAP_ATMEGA2560 // (Arduino Mega 2560) Working @EliteEng
+  #ifdef CPU_MAP_ATMEGA2560 // (Arduino Mega 2560) Working @EliteEng
 
   // Serial port pins
   #define SERIAL_RX USART0_RX_vect
   #define SERIAL_UDRE USART0_UDRE_vect
 
   // Increase Buffers to make use of extra SRAM
-  #define RX_BUFFER_SIZE 256
-  #define TX_BUFFER_SIZE 128
-  #define BLOCK_BUFFER_SIZE 36
-  #define LINE_BUFFER_SIZE 100
+  //#define RX_BUFFER_SIZE		256
+  //#define TX_BUFFER_SIZE		128
+  //#define BLOCK_BUFFER_SIZE	36
+  //#define LINE_BUFFER_SIZE	100
 
   // NOTE: All step pins must be on the same port.
   #define STEPPING_DDR      DDRA
@@ -121,7 +175,7 @@
   #define X_STEP_BIT        2 // MEGA2560 Digital Pin 24
   #define Y_STEP_BIT        3 // MEGA2560 Digital Pin 25
   #define Z_STEP_BIT        4 // MEGA2560 Digital Pin 26
-  #define STEPPING_MASK ((1<<X_STEP_BIT)|(1<<Y_STEP_BIT)|(1<<Z_STEP_BIT)) // All step bits
+  #define STEP_MASK ((1<<X_STEP_BIT)|(1<<Y_STEP_BIT)|(1<<Z_STEP_BIT)) // All step bits
 
   // NOTE: All direction pins must be on the same port.
   #define DIRECTION_DDR      DDRA
@@ -149,23 +203,33 @@
   #define LIMIT_PCMSK     PCMSK0 // Pin change interrupt register
   #define LIMIT_MASK ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)) // All limit bits
 
-  #define SPINDLE_ENABLE_DDR   DDRC
-  #define SPINDLE_ENABLE_PORT  PORTC
-  #define SPINDLE_ENABLE_BIT   2 // MEGA2560 Digital Pin 35
+  // WARNING if INVERT_SPINDLE is defined the pin will be LOW(Active) on reset of controller until spindle_init() is called.
+  // this should only be a very short period of time but will energise the spindle.
+  // #define INVERT_SPINDLE // This will INVERT the Spindle LOW=Active
+  // END WARNING
 
-  #define SPINDLE_DIRECTION_DDR   DDRC
-  #define SPINDLE_DIRECTION_PORT  PORTC
-  #define SPINDLE_DIRECTION_BIT   1 // MEGA2560 Digital Pin 36
+  #define SPINDLE_ENABLE_DDR   DDRH
+  #define SPINDLE_ENABLE_PORT  PORTH
+  #define SPINDLE_ENABLE_BIT   3 // MEGA2560 Digital Pin 6
 
-  #define COOLANT_FLOOD_DDR   DDRC
-  #define COOLANT_FLOOD_PORT  PORTC
-  #define COOLANT_FLOOD_BIT   0 // MEGA2560 Digital Pin 37
+  #define SPINDLE_DIRECTION_DDR   DDRE
+  #define SPINDLE_DIRECTION_PORT  PORTE
+  #define SPINDLE_DIRECTION_BIT   3 // MEGA2560 Digital Pin 5
+
+  // WARNING if INVERT_COOLANT is defined the pin will be LOW(Active) on reset of controller until coolant_init() is called.
+  // this should only be a very short period of time but will energise the coolant pump.
+  // #define INVERT_COOLANT // This will INVERT the Coolant LOW=Active
+  // END WARNING
+
+  #define COOLANT_FLOOD_DDR   DDRH
+  #define COOLANT_FLOOD_PORT  PORTH
+  #define COOLANT_FLOOD_BIT   5 // MEGA2560 Digital Pin 8
 
   // #define ENABLE_M7  // Mist coolant disabled by default. Uncomment to enable.
   #ifdef ENABLE_M7
-    #define COOLANT_MIST_DDR   DDRC
-    #define COOLANT_MIST_PORT  PORTC
-    #define COOLANT_MIST_BIT   3 // MEGA2560 Digital Pin 34
+    #define COOLANT_MIST_DDR   DDRH
+    #define COOLANT_MIST_PORT  PORTH
+    #define COOLANT_MIST_BIT   6 // MEGA2560 Digital Pin 9
   #endif  
 
   // NOTE: All pinouts pins must be on the same port and cannot be on same port as limit pins.
@@ -180,11 +244,41 @@
   #define PINOUT_PCMSK     PCMSK2 // Pin change interrupt register
   #define PINOUT_MASK ((1<<PIN_RESET)|(1<<PIN_FEED_HOLD)|(1<<PIN_CYCLE_START))
 
-#endif
+  // Start of PWM & Stepper Enabled Spindle
+  // #define VARIABLE_SPINDLE // comment this out to disable PWM & Stepper on the spindle
+  #ifdef VARIABLE_SPINDLE
+
+  //#define SPINDLE_IS_STEPPER // Uncomment this if your Spindle is a Stepper Motor
+  #define SPINDLE_IS_PWM // Uncomment this if your Spindle uses PWM ie. DC Motor
+
+    #ifdef SPINDLE_IS_PWM
+      #define SPINDLE_MAX_RPM		255 // Max RPM of your spindle
+    #endif
+
+  // Advanced Configuration Below You should not need to touch these variables
+
+  //Set Timer up to use TIMER4 OCR4B which is attached to Digital Pin 7
+  #define TCCRA_REGISTER		TCCR2A
+  #define TCCRB_REGISTER		TCCR2B
+  #define OCR_REGISTER		OCR2B
+
+  #define COMB_BIT			COM2B1
+  #define WAVE0_REGISTER		WGM20
+  #define WAVE1_REGISTER		WGM21
+  #define WAVE2_REGISTER		WGM22
+  #define WAVE3_REGISTER		WGM23
+
+  #define SPINDLE_PWM_DDR		DDRH
+  #define SPINDLE_PWM_PORT		PORTH
+  #define SPINDLE_PWM_BIT		6 // MEGA2560 Digital Pin 9
+
+  #endif // End of VARIABLE_SPINDLE
+  #endif
 
 /* 
 #ifdef CPU_MAP_CUSTOM_PROC
   // For a custom pin map or different processor, copy and paste one of the default cpu map
+
   // settings above and modify it to your needs. Then, make sure the defined name is also
   // changed in the config.h file.
 #endif
diff --git a/gcode.c b/gcode.c
index eeaa433..990cb88 100644
--- a/gcode.c
+++ b/gcode.c
@@ -238,8 +238,7 @@ uint8_t gc_execute_line(char *line)
       case 'R': gc.arc_radius = to_millimeters(value); break;
       case 'S': 
         if (value < 0) { FAIL(STATUS_INVALID_STATEMENT); } // Cannot be negative
-        // TBD: Spindle speed not supported due to PWM issues, but may come back once resolved.
-        // gc.spindle_speed = value;
+           gc.spindle_speed = value;
         break;
       case 'T': 
         if (value < 0) { FAIL(STATUS_INVALID_STATEMENT); } // Cannot be negative
@@ -266,7 +265,7 @@ uint8_t gc_execute_line(char *line)
     //  ([M6]: Tool change should be executed here.)
 
     // [M3,M4,M5]: Update spindle state
-    spindle_run(gc.spindle_direction);
+    spindle_run(gc.spindle_direction, gc.spindle_speed);
   
     // [*M7,M8,M9]: Update coolant state
     coolant_run(gc.coolant_mode);
diff --git a/gcode.h b/gcode.h
index 334c78a..aebc0ba 100644
--- a/gcode.h
+++ b/gcode.h
@@ -75,7 +75,7 @@ typedef struct {
   float feed_rate;                 // Millimeters/min
   float position[N_AXIS];          // Where the interpreter considers the tool to be at this point in the code
   uint8_t tool;
-//  uint16_t spindle_speed;          // RPM/100
+  uint16_t spindle_speed;          // RPM
   uint8_t plane_axis_0, 
           plane_axis_1, 
           plane_axis_2;            // The axes of the selected plane  
diff --git a/spindle_control.c b/spindle_control.c
index 5786762..5dfab0b 100644
--- a/spindle_control.c
+++ b/spindle_control.c
@@ -24,34 +24,74 @@
 #include "planner.h"
 
 static uint8_t current_direction;
+static uint16_t current_rpm;
+static uint8_t current_pwm;
 
 void spindle_init()
 {
   current_direction = 0;
   SPINDLE_ENABLE_DDR |= (1<<SPINDLE_ENABLE_BIT);
-  SPINDLE_DIRECTION_DDR |= (1<<SPINDLE_DIRECTION_BIT);  
+  SPINDLE_DIRECTION_DDR |= (1<<SPINDLE_DIRECTION_BIT);
+  
+#ifdef VARIABLE_SPINDLE
+        SPINDLE_PWM_DDR |= (1<<SPINDLE_PWM_BIT);
+#endif 
+  
   spindle_stop();
 }
 
 void spindle_stop()
 {
-  SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
+#ifdef INVERT_SPINDLE
+        SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+#else
+        SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
+#endif
+#ifdef VARIABLE_SPINDLE
+        TCCRA_REGISTER &= ~(1<<COMB_BIT);
+#endif
 }
 
-void spindle_run(int8_t direction) //, uint16_t rpm) 
-{
-  if (direction != current_direction) {
-    plan_synchronize();
-    if (direction) {
-      if(direction > 0) {
-        SPINDLE_DIRECTION_PORT &= ~(1<<SPINDLE_DIRECTION_BIT);
-      } else {
-        SPINDLE_DIRECTION_PORT |= 1<<SPINDLE_DIRECTION_BIT;
-      }
-      SPINDLE_ENABLE_PORT |= 1<<SPINDLE_ENABLE_BIT;
-    } else {
-      spindle_stop();     
-    }
-    current_direction = direction;
-  }
+void spindle_run(int8_t direction, uint16_t rpm) {
+	if ((direction != current_direction) || (rpm != current_rpm)) {
+		plan_synchronize();
+	if (direction) {
+		if (direction > 0) {
+			SPINDLE_DIRECTION_PORT &= ~(1<<SPINDLE_DIRECTION_BIT);
+		} else {
+			SPINDLE_DIRECTION_PORT |= (1<<SPINDLE_DIRECTION_BIT);
+		}
+
+#ifdef VARIABLE_SPINDLE
+#ifdef SPINDLE_IS_PWM
+
+	TCCRA_REGISTER = (1<<COMB_BIT) | (1<<WAVE1_REGISTER) | (1<<WAVE0_REGISTER);
+	TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x02; // set to 1/8 Prescaler
+	current_pwm = floor((((float) rpm / (float) SPINDLE_MAX_RPM ) * 255.0) + 0.5);
+	OCR_REGISTER = current_pwm;
+	
+#endif
+#endif
+#ifdef INVERT_SPINDLE
+        SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
+#else
+        SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+#endif
+
+	} else {
+		spindle_stop();
+	}
+                current_direction = direction;
+                current_rpm = rpm;
+	}
+}
+
+uint8_t spindle_pwm()
+{
+	return current_pwm;
+}
+
+void spindle_pwm_update(uint8_t pwm)
+{
+	OCR_REGISTER = pwm;
 }
diff --git a/spindle_control.h b/spindle_control.h
index ba8f051..4af96f1 100644
--- a/spindle_control.h
+++ b/spindle_control.h
@@ -25,7 +25,9 @@
 #include <avr/io.h>
 
 void spindle_init();
-void spindle_run(int8_t direction); //, uint16_t rpm);
+void spindle_run(int8_t direction, uint16_t rpm);
 void spindle_stop();
+uint8_t spindle_pwm();
+void spindle_pwm_update(uint8_t pwm);
 
 #endif