diff --git a/config.h b/config.h
index daa6268..4cb4de5 100644
--- a/config.h
+++ b/config.h
@@ -86,10 +86,24 @@
 // acceleration, particularly noticeable on machines that run at very high feedrates, but may negatively
 // impact performance. The correct value for this parameter is machine dependent, so it's advised to
 // set this only as high as needed. Approximate successful values can widely range from 50 to 200 or more.
+// NOTE: Changing this value also changes the execution time of a segment in the step segment buffer. 
+// When increasing this value, this stores less overall time in the segment buffer and vice versa. Make
+// certain the step segment buffer is increased/decreased to account for these changes.
 #define ACCELERATION_TICKS_PER_SECOND 100 
 
-#define ADAPTIVE_MULTI_AXIS_STEP_SMOOTHING 
-#define ENABLE_SOFTWARE_DEBOUNCE
+// Adaptive Multi-Axis Step Smoothing (AMASS) is an advanced feature that does what its name implies, 
+// smoothing the stepping of multi-axis motions. This feature smooths motion particularly at low step
+// frequencies below 10kHz, where the aliasing between axes of multi-axis motions can cause audible 
+// noise and shake your machine. At even lower step frequencies, AMASS adapts and provides even better
+// step smoothing. See stepper.c for more details on the AMASS system works.
+#define ADAPTIVE_MULTI_AXIS_STEP_SMOOTHING  // Default enabled. Comment to disable.
+
+// Enables variable spindle output voltage for different RPM values. On the Arduino Uno, the spindle
+// enable pin will output 5V for maximum RPM with 256 intermediate levels and 0V when disabled.
+// NOTE: IMPORTANT for Arduino Unos! When enabled, the Z-limit pin D11 and spindle enable pin D12 switch!
+// The hardware PWM output on pin D11 is required for variable spindle output voltages.
+// #define VARIABLE_SPINDLE // Default disabled. Uncomment to enable.
+// #define SPINDLE_MAX_RPM 1000 // Max spindle RPM. This value is equal to 100% Duty Cycle on the PWM.
 
 // Minimum planner junction speed. Sets the default minimum junction speed the planner plans to at
 // every buffer block junction, except for starting from rest and end of the buffer, which are always
@@ -168,6 +182,14 @@
 // case, please report any successes to grbl administrators!
 // #define ENABLE_XONXOFF // Default disabled. Uncomment to enable.
 
+// A simple software debouncing feature for hard limit switches. When enabled, the interrupt monitoring
+// the hard limit switch pins will enable the Arduino's watchdog timer to re-check the limit pin state
+// after a delay of about 32msec. This can help with CNC machines with problematic false triggering of 
+// their hard limit switches, but it WILL NOT fix issues with electrical interference on the signal 
+// cables from external sources. It's recommended to first use shielded signal cables that are grounded
+// (old USB/computer cables work well) and wire in a low-pass circuit into each limit pin.
+// #define ENABLE_SOFTWARE_DEBOUNCE // Default disabled. Uncomment to enable.
+
 // ---------------------------------------------------------------------------------------
 
 // TODO: Install compile-time option to send numeric status codes rather than strings.
diff --git a/coolant_control.c b/coolant_control.c
index 90cde68..b849a78 100644
--- a/coolant_control.c
+++ b/coolant_control.c
@@ -27,29 +27,24 @@
 
 static uint8_t current_coolant_mode;
 
+
 void coolant_init()
 {
   current_coolant_mode = COOLANT_DISABLE;
-  #if ENABLE_M7
+  COOLANT_FLOOD_DDR |= (1 << COOLANT_FLOOD_BIT);
+  #ifdef ENABLE_M7
     COOLANT_MIST_DDR |= (1 << COOLANT_MIST_BIT);
   #endif
-  COOLANT_FLOOD_DDR |= (1 << COOLANT_FLOOD_BIT);
   coolant_stop();
 }
 
+
 void coolant_stop()
 {
-#ifdef INVERT_COOLANT
+  COOLANT_FLOOD_PORT &= ~(1 << COOLANT_FLOOD_BIT);
   #ifdef ENABLE_M7
-    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
+    COOLANT_MIST_PORT &= ~(1 << COOLANT_MIST_BIT);
+  #endif
 }
 
 
@@ -59,19 +54,13 @@ void coolant_run(uint8_t mode)
   { 
     plan_synchronize(); // Ensure coolant turns on when specified in program.
     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
+      COOLANT_FLOOD_PORT |= (1 << COOLANT_FLOOD_BIT);
+  
+  #ifdef ENABLE_M7  
+    } else if (mode == COOLANT_MIST_ENABLE) {
+      COOLANT_MIST_PORT |= (1 << COOLANT_MIST_BIT);
+  #endif
+
     } else {
       coolant_stop();
     }
diff --git a/cpu_map.h b/cpu_map.h
index 70a3984..bbc006b 100644
--- a/cpu_map.h
+++ b/cpu_map.h
@@ -28,94 +28,82 @@
 #ifndef cpu_map_h
 #define cpu_map_h
 
+//----------------------------------------------------------------------------------------
+
 #ifdef CPU_MAP_ATMEGA328P // (Arduino Uno) Officially supported by Grbl.
 
-  // Serial port pins
+  // Define serial port pins and interrupt vectors.
   #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
-  #define X_STEP_BIT         2  // Uno Digital Pin 2
-  #define Y_STEP_BIT         3  // Uno Digital Pin 3
-  #define Z_STEP_BIT         4  // Uno Digital Pin 4
-  #define STEP_MASK ((1<<X_STEP_BIT)|(1<<Y_STEP_BIT)|(1<<Z_STEP_BIT)) // All step bits
+  // Define step pulse output pins. NOTE: All step bit pins must be on the same port.
+  #define STEPPING_DDR    DDRD
+  #define STEPPING_PORT   PORTD
+  #define X_STEP_BIT      2  // Uno Digital Pin 2
+  #define Y_STEP_BIT      3  // Uno Digital Pin 3
+  #define Z_STEP_BIT      4  // Uno Digital Pin 4
+  #define STEP_MASK       ((1<<X_STEP_BIT)|(1<<Y_STEP_BIT)|(1<<Z_STEP_BIT)) // All step bits
 
-  #define DIRECTION_DDR       DDRD
-  #define DIRECTION_PORT      PORTD
-  #define X_DIRECTION_BIT    5  // Uno Digital Pin 5
-  #define Y_DIRECTION_BIT    6  // Uno Digital Pin 6
-  #define Z_DIRECTION_BIT    7  // Uno Digital Pin 7
-  #define DIRECTION_MASK ((1<<X_DIRECTION_BIT)|(1<<Y_DIRECTION_BIT)|(1<<Z_DIRECTION_BIT)) // All direction bits
+  // Define step direction output pins. NOTE: All direction pins must be on the same port.
+  #define DIRECTION_DDR     DDRD
+  #define DIRECTION_PORT    PORTD
+  #define X_DIRECTION_BIT   5  // Uno Digital Pin 5
+  #define Y_DIRECTION_BIT   6  // Uno Digital Pin 6
+  #define Z_DIRECTION_BIT   7  // Uno Digital Pin 7
+  #define DIRECTION_MASK    ((1<<X_DIRECTION_BIT)|(1<<Y_DIRECTION_BIT)|(1<<Z_DIRECTION_BIT)) // All direction bits
 
+  // Define stepper driver enable/disable output pin.
   #define STEPPERS_DISABLE_DDR    DDRB
   #define STEPPERS_DISABLE_PORT   PORTB
   #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
+  #define STEPPERS_DISABLE_MASK   (1<<STEPPERS_DISABLE_BIT)
 
+  // Define homing/hard limit switch input pins and limit interrupt vectors. 
+  // NOTE: All limit bit pins must be on the same port, but not on a port with other input pins (pinout).
+  #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 10
+  #ifdef VARIABLE_SPINDLE // Z Limit pin and spindle enabled swapped to access hardware PWM on Pin 11.  
+    #define Z_LIMIT_BIT	   4 // Uno Digital Pin 12
   #else
-  // 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 10
-  #define Z_LIMIT_BIT     3  // 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)|(1<<Z_LIMIT_BIT)) // All limit bits
+    #define Z_LIMIT_BIT    3  // Uno Digital Pin 11
   #endif
+  #define LIMIT_MASK       ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)) // All limit bits
+  #define LIMIT_INT        PCIE0  // Pin change interrupt enable pin
+  #define LIMIT_INT_vect   PCINT0_vect 
+  #define LIMIT_PCMSK      PCMSK0 // Pin change interrupt register
 
-  // 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
-  #define SPINDLE_ENABLE_BIT   4  // Uno Digital Pin 12
-
+  // Define spindle enable and spindle direction output pins.
+  #define SPINDLE_ENABLE_DDR    DDRB
+  #define SPINDLE_ENABLE_PORT   PORTB
+  #ifdef VARIABLE_SPINDLE // Z Limit pin and spindle enabled swapped to access hardware PWM on Pin 11.  
+    #define SPINDLE_ENABLE_BIT    3  // Uno Digital Pin 11
+  #else
+    #define SPINDLE_ENABLE_BIT    4  // Uno Digital Pin 12
+  #endif  
   #define SPINDLE_DIRECTION_DDR   DDRB
   #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 flood and mist coolant enable output pins.
+  // NOTE: Uno analog pins 4 and 5 are reserved for an i2c interface, and may be installed at
+  // a later date if flash and memory space allows.
   #define COOLANT_FLOOD_DDR   DDRC
   #define COOLANT_FLOOD_PORT  PORTC
   #define COOLANT_FLOOD_BIT   3  // Uno Analog Pin 3
-
-  // NOTE: Uno analog pins 4 and 5 are reserved for an i2c interface, and may be installed at
-  // a later date if flash and memory space allows.
-  // #define ENABLE_M7  // Mist coolant disabled by default. Uncomment to enable.
-  #ifdef ENABLE_M7
+  #ifdef ENABLE_M7 // Mist coolant disabled by default. See config.h to enable/disable.
     #define COOLANT_MIST_DDR   DDRC
     #define COOLANT_MIST_PORT  PORTC
     #define COOLANT_MIST_BIT   4 // Uno Analog Pin 4
   #endif  
 
-  // NOTE: All pinouts pins must be on the same port, but cannot be on same port as limit pins.
+  // Define user-control pinouts (cycle start, reset, feed hold) input pins.
+  // NOTE: All pinouts pins must be on the same port and not on a port with other input pins (limits).
   #define PINOUT_DDR       DDRC
   #define PINOUT_PIN       PINC
   #define PINOUT_PORT      PORTC
@@ -128,35 +116,28 @@
   #define PINOUT_MASK ((1<<PIN_RESET)|(1<<PIN_FEED_HOLD)|(1<<PIN_CYCLE_START))
   
   #ifdef VARIABLE_SPINDLE
+    // Advanced Configuration Below You should not need to touch these variables
+    #define TCCRA_REGISTER	 TCCR2A
+    #define TCCRB_REGISTER	 TCCR2B
+    #define OCR_REGISTER     OCR2A
 
-  #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
+    #define COMB_BIT	     COM2A1
+    #define WAVE0_REGISTER	 WGM20
+    #define WAVE1_REGISTER	 WGM21
+    #define WAVE2_REGISTER	 WGM22
+    #define WAVE3_REGISTER	 WGM23
 
+    // NOTE: On the 328p, these must be the same as the SPINDLE_ENABLE settings.
+    #define SPINDLE_PWM_DDR	  SPINDLE_ENABLE_DDR
+    #define SPINDLE_PWM_PORT  SPINDLE_ENABLE_PORT
+    #define SPINDLE_PWM_BIT	  SPINDLE_ENABLE_BIT // Shared with SPINDLE_ENABLE.
   #endif // End of VARIABLE_SPINDLE
-  #endif
 
+#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
@@ -168,7 +149,7 @@
   //#define BLOCK_BUFFER_SIZE	36
   //#define LINE_BUFFER_SIZE	100
 
-  // NOTE: All step pins must be on the same port.
+  // Define step pulse output pins. NOTE: All step bit pins must be on the same port.
   #define STEPPING_DDR      DDRA
   #define STEPPING_PORT     PORTA
   #define STEPPING_PIN      PINA
@@ -177,7 +158,7 @@
   #define Z_STEP_BIT        4 // MEGA2560 Digital Pin 26
   #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 step direction output pins. NOTE: All direction pins must be on the same port.
   #define DIRECTION_DDR      DDRA
   #define DIRECTION_PORT     PORTA
   #define DIRECTION_PIN      PINA
@@ -186,6 +167,7 @@
   #define Z_DIRECTION_BIT   7 // MEGA2560 Digital Pin 29
   #define DIRECTION_MASK ((1<<X_DIRECTION_BIT)|(1<<Y_DIRECTION_BIT)|(1<<Z_DIRECTION_BIT)) // All direction bits
 
+  // Define stepper driver enable/disable output pin.
   #define STEPPERS_DISABLE_DDR   DDRB
   #define STEPPERS_DISABLE_PORT  PORTB
   #define STEPPERS_DISABLE_BIT   7 // MEGA2560 Digital Pin 13
@@ -203,36 +185,28 @@
   #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
 
-  // 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 and spindle direction output pins.
   #define SPINDLE_ENABLE_DDR   DDRH
   #define SPINDLE_ENABLE_PORT  PORTH
   #define SPINDLE_ENABLE_BIT   3 // MEGA2560 Digital Pin 6
-
   #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 flood and mist coolant enable output pins.
+  // NOTE: Uno analog pins 4 and 5 are reserved for an i2c interface, and may be installed at
+  // a later date if flash and memory space allows.
   #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
+  #ifdef ENABLE_M7 // Mist coolant disabled by default. See config.h to enable/disable.
     #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.
+  // Define user-control pinouts (cycle start, reset, feed hold) input pins.
+  // NOTE: All pinouts pins must be on the same port and not on a port with other input pins (limits).
   #define PINOUT_DDR       DDRK
   #define PINOUT_PIN       PINK
   #define PINOUT_PORT      PORTK
@@ -245,40 +219,31 @@
   #define PINOUT_MASK ((1<<PIN_RESET)|(1<<PIN_FEED_HOLD)|(1<<PIN_CYCLE_START))
 
   // Start of PWM & Stepper Enabled Spindle
-  // #define VARIABLE_SPINDLE // comment this out to disable PWM & Stepper on the spindle
   #ifdef VARIABLE_SPINDLE
+    // 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 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
+    #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
+
+#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/limits.c b/limits.c
index a9e15f2..0abbc7d 100644
--- a/limits.c
+++ b/limits.c
@@ -55,7 +55,7 @@ void limits_init()
   #ifdef ENABLE_SOFTWARE_DEBOUNCE
     MCUSR &= ~(1<<WDRF);
     WDTCSR |= (1<<WDCE) | (1<<WDE);
-    WDTCSR = (1<<WDP0);
+    WDTCSR = (1<<WDP0); // Set time-out at ~32msec.
   #endif
 }
 
diff --git a/spindle_control.c b/spindle_control.c
index 5dfab0b..615d57c 100644
--- a/spindle_control.c
+++ b/spindle_control.c
@@ -25,73 +25,71 @@
 
 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);
   
-#ifdef VARIABLE_SPINDLE
-        SPINDLE_PWM_DDR |= (1<<SPINDLE_PWM_BIT);
-#endif 
+  // On the Uno, spindle enable and PWM are shared. Other CPUs have seperate enable pin.
+  #ifdef VARIABLE_SPINDLE
+    SPINDLE_PWM_DDR |= (1<<SPINDLE_PWM_BIT);
+    #ifndef CPU_MAP_ATMEGA328P 
+      SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+    #endif     
+  #else
+    SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+  #endif
   
   spindle_stop();
 }
 
+
 void spindle_stop()
 {
-#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
+  // On the Uno, spindle enable and PWM are shared. Other CPUs have seperate enable pin.
+  #ifdef VARIABLE_SPINDLE
+    TCCRA_REGISTER &= ~(1<<COMB_BIT); // Disable PWM. Output voltage is zero.
+    #ifndef CPU_MAP_ATMEGA328P 
+      SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
+    #endif
+  #else
+    SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
+  #endif  
 }
 
-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
+void spindle_run(int8_t direction, uint16_t rpm) 
+{
+  if ((direction != current_direction) || (rpm != current_rpm)) {
+    plan_synchronize(); // Empty planner buffer to ensure spindle is updated as programmed.
+    if (direction) {
+      if (direction > 0) {
+        SPINDLE_DIRECTION_PORT &= ~(1<<SPINDLE_DIRECTION_BIT);
+      } else {
+        SPINDLE_DIRECTION_PORT |= (1<<SPINDLE_DIRECTION_BIT);
+      }
 
-	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
+      #ifdef VARIABLE_SPINDLE
+        TCCRA_REGISTER = (1<<COMB_BIT) | (1<<WAVE1_REGISTER) | (1<<WAVE0_REGISTER);
+        TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x02; // set to 1/8 Prescaler
+        if (rpm > SPINDLE_MAX_RPM) { rpm = SPINDLE_MAX_RPM; } // Prevent overflow.
+        uint8_t current_pwm = floor((((float) rpm / (float) SPINDLE_MAX_RPM ) * 255.0) + 0.5);
+        OCR_REGISTER = current_pwm;
+        
+        #ifndef CPU_MAP_ATMEGA328P // On the Uno, spindle enable and PWM are shared.
+          SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+        #endif
+      #else   
         SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
-#endif
-
+      #endif
+          
 	} else {
-		spindle_stop();
-	}
-                current_direction = direction;
-                current_rpm = rpm;
+      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;
-}
+#endif
diff --git a/spindle_control.h b/spindle_control.h
index 4af96f1..e428a70 100644
--- a/spindle_control.h
+++ b/spindle_control.h
@@ -24,10 +24,13 @@
 
 #include <avr/io.h>
 
+// Initializes spindle pins and hardware PWM, if enabled.
 void spindle_init();
+
+// Sets spindle direction and spindle rpm via PWM, if enabled.
 void spindle_run(int8_t direction, uint16_t rpm);
+
+// Kills spindle.
 void spindle_stop();
-uint8_t spindle_pwm();
-void spindle_pwm_update(uint8_t pwm);
 
 #endif