diff --git a/Grbl_Esp32/cpu_map.h b/Grbl_Esp32/cpu_map.h
index 71052a8b..9a0bd58a 100644
--- a/Grbl_Esp32/cpu_map.h
+++ b/Grbl_Esp32/cpu_map.h
@@ -57,97 +57,96 @@
 	running so OTA (over the air) firmware loading can be done.
 
 	*/
-	#define CPU_MAP_NAME "CPU_MAP_DEFAULT - Demo Only No I/O!"
-	
+	#define CPU_MAP_NAME "CPU_MAP_DEFAULT - Demo Only No I/O!"	
 	
 	// the following items currently need to be defined, but no i/o needs to be mapped
 	// fixing soon
 	
-	#define LIMIT_MASK 0  // no limit pins
+	#define LIMIT_MASK 0  // no limit pins		
+#endif
+
+#ifdef CPU_MAP_ESP32
+	// This is the CPU Map for the ESP32 Development Controller
+	// https://github.com/bdring/Grbl_ESP32_Development_Controller
+	// https://www.tindie.com/products/33366583/grbl_esp32-cnc-development-board-v35/
+	
+	// Select the version (uncomment one of them)
+	#define CPU_MAP_V3p5 // version 3.5 and earlier
+	//#define CPU_MAP_V4 // version 4 or higher (in developement) 
+	
+	#define USE_RMT_STEPS
+	
+	// It is OK to comment out any step and direction pins. This
+    // won't affect operation except that there will be no output
+	// form the pins. Grbl will virtually move the axis. This could 
+	// be handy if you are using a servo, etc. for another axis.
+	#if (defined CPU_MAP_V4)
+		#define CPU_MAP_NAME 		"CPU_MAP_ESP32_V4"
+		#define X_DIRECTION_PIN  	GPIO_NUM_14
+		#define Y_STEP_PIN      	GPIO_NUM_26
+		#define Y_DIRECTION_PIN   	GPIO_NUM_15
+		#define COOLANT_FLOOD_PIN 	GPIO_NUM_25
+		#define SPINDLE_PWM_PIN    	GPIO_NUM_2
+		#define X_LIMIT_PIN      	GPIO_NUM_17
+		#define Z_LIMIT_PIN     	GPIO_NUM_16		
+	#elif (defined CPU_MAP_V3p5)
+		#define CPU_MAP_NAME 		"CPU_MAP_ESP32_V3.5"
+		#define X_DIRECTION_PIN  	GPIO_NUM_26
+		#define Y_STEP_PIN      	GPIO_NUM_14
+		#define Y_DIRECTION_PIN   	GPIO_NUM_25
+		#define COOLANT_FLOOD_PIN 	GPIO_NUM_16
+		#define SPINDLE_PWM_PIN    	GPIO_NUM_17
+		#define X_LIMIT_PIN      	GPIO_NUM_2
+		#define Z_LIMIT_PIN     	GPIO_NUM_15 
+	#endif
+	
+	#define X_STEP_PIN      	GPIO_NUM_12
+	
+	#define X_RMT_CHANNEL		0
+	
+	// #define Y_STEP_PIN (see versions above) 	
+	#define Y_RMT_CHANNEL		1
+	
+	#define Z_STEP_PIN      	GPIO_NUM_27		
+	#define Z_DIRECTION_PIN   	GPIO_NUM_33		 
+	#define Z_RMT_CHANNEL		2		
+	
+	// OK to comment out to use pin for other features
+	#define STEPPERS_DISABLE_PIN GPIO_NUM_13		
+		
+	#define COOLANT_MIST_PIN   	GPIO_NUM_21
+		
+	
 	
 	#define SPINDLE_PWM_CHANNEL 0
+	// PWM Generator is based on 80,000,000 Hz counter
+	// Therefor the freq determines the resolution
+	// 80,000,000 / freq = max resolution
+	// For 5000 that is 80,000,000 / 5000 = 16000 
+	// round down to nearest bit count for SPINDLE_PWM_MAX_VALUE = 13bits (8192)
+	
 	#define SPINDLE_PWM_BASE_FREQ 5000 // Hz
-	#define SPINDLE_PWM_BIT_PRECISION 8   // be sure to match this with SPINDLE_PWM_MAX_VALUE
+	#define SPINDLE_PWM_BIT_PRECISION 8   
 	#define SPINDLE_PWM_OFF_VALUE     0
-	#define SPINDLE_PWM_MAX_VALUE     255 // (2^SPINDLE_PWM_BIT_PRECISION)
+	#define SPINDLE_PWM_MAX_VALUE     255
+	//#define INVERT_SPINDLE_PWM
 	
 	#ifndef SPINDLE_PWM_MIN_VALUE
-			#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
+		#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
 	#endif
 	
 	#define SPINDLE_ENABLE_PIN	GPIO_NUM_22
 	
-	#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)	
-#endif
-
-#ifdef CPU_MAP_ESP32
-	// This is the CPU Map for the ESP32 CNC Controller R2	
+	// see versions for X and Z
+	#define Y_LIMIT_PIN      	GPIO_NUM_4	
+	#define LIMIT_MASK      	B111
 	
-	  // It is OK to comment out any step and direction pins. This
-    // won't affect operation except that there will be no output
-		// form the pins. Grbl will virtually move the axis. This could 
-		// be handy if you are using a servo, etc. for another axis.
-		#define CPU_MAP_NAME "CPU_MAP_ESP32"	
-		
-		#define X_STEP_PIN      	GPIO_NUM_12
-		#define X_DIRECTION_PIN  	GPIO_NUM_26
-		#define X_RMT_CHANNEL		0
-		
-		#define Y_STEP_PIN      	GPIO_NUM_14
-		#define Y_DIRECTION_PIN   	GPIO_NUM_25
-		#define Y_RMT_CHANNEL		1
-		
-		#define Z_STEP_PIN      	GPIO_NUM_27		
-		#define Z_DIRECTION_PIN   	GPIO_NUM_33 		 
-		#define Z_RMT_CHANNEL		2		
-		
-		// OK to comment out to use pin for other features
-		#define STEPPERS_DISABLE_PIN GPIO_NUM_13		
-		
-		// *** the flood coolant feature code is activated by defining this pins
-		// *** Comment it out to use the pin for other features
-		#define COOLANT_FLOOD_PIN 	GPIO_NUM_16			
-		//#define COOLANT_MIST_PIN   	GPIO_NUM_21
-		
-		// If SPINDLE_PWM_PIN is commented out, this frees up the pin, but Grbl will still
-		// use a virtual spindle. Do not comment out the other parameters for the spindle.
-		#define SPINDLE_PWM_PIN    GPIO_NUM_17 
-		#define SPINDLE_PWM_CHANNEL 0
-		// PWM Generator is based on 80,000,000 Hz counter
-		// Therefor the freq determines the resolution
-		// 80,000,000 / freq = max resolution
-		// For 5000 that is 80,000,000 / 5000 = 16000 
-		// round down to nearest bit count for SPINDLE_PWM_MAX_VALUE = 13bits (8192)
-		#define SPINDLE_PWM_BASE_FREQ 5000 // Hz
-		#define SPINDLE_PWM_BIT_PRECISION 8   // be sure to match this with SPINDLE_PWM_MAX_VALUE
-		#define SPINDLE_PWM_OFF_VALUE     0
-		#define SPINDLE_PWM_MAX_VALUE     255 // (2^SPINDLE_PWM_BIT_PRECISION)
-		
-		#ifndef SPINDLE_PWM_MIN_VALUE
-				#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
-		#endif
-		
-		#define SPINDLE_ENABLE_PIN	GPIO_NUM_22
-		
-		#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)				
-		
-		// if these spindle function pins are defined, they will be activated in the code
-		// comment them out to use the pins for other functions
-		//#define SPINDLE_ENABLE_PIN	GPIO_NUM_16
-		//#define SPINDLE_DIR_PIN			GPIO_NUM_16		
-		
-		#define X_LIMIT_PIN      	GPIO_NUM_2  
-		#define Y_LIMIT_PIN      	GPIO_NUM_4  
-		#define Z_LIMIT_PIN     	GPIO_NUM_15 	
-		#define LIMIT_MASK      	B111
-		
-		#define PROBE_PIN       	GPIO_NUM_32  
-		
-		#define CONTROL_SAFETY_DOOR_PIN   GPIO_NUM_35  // needs external pullup
-		#define CONTROL_RESET_PIN         GPIO_NUM_34  // needs external pullup
-		#define CONTROL_FEED_HOLD_PIN     GPIO_NUM_36  // needs external pullup 
-		#define CONTROL_CYCLE_START_PIN   GPIO_NUM_39  // needs external pullup    		
-		
+	#define PROBE_PIN       	GPIO_NUM_32  
+	
+	#define CONTROL_SAFETY_DOOR_PIN   GPIO_NUM_35  // needs external pullup
+	#define CONTROL_RESET_PIN         GPIO_NUM_34  // needs external pullup
+	#define CONTROL_FEED_HOLD_PIN     GPIO_NUM_36  // needs external pullup 
+	#define CONTROL_CYCLE_START_PIN   GPIO_NUM_39  // needs external pullup 
 #endif
 
 #ifdef CPU_MAP_ESPDUINO_32
@@ -189,7 +188,6 @@
 			#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
 	#endif	
 	
-	#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)		
 	
 	#define SPINDLE_DIR_PIN		GPIO_NUM_18	// Uno D13
 	
@@ -259,9 +257,7 @@
 		#ifndef SPINDLE_PWM_MIN_VALUE
 				#define SPINDLE_PWM_MIN_VALUE   SPINDLE_PWM_OFF_VALUE   // Must be greater than zero.
 		#endif
-		
-		#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)
-		
+				
 		#define SPINDLE_ENABLE_PIN	GPIO_NUM_22			
 		
 		// if these spindle function pins are defined, they will be activated in the code
@@ -334,9 +330,7 @@
 		
 		#ifndef SPINDLE_PWM_MIN_VALUE
 				#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
-		#endif
-		
-		#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)			
+		#endif			
 		
 		#define USING_SERVO  // uncomment to use this feature
 		//#define USING_SOLENOID // uncomment to use this feature
@@ -484,9 +478,7 @@
 		#ifdef DEFAULTS_GENERIC
 			#undef DEFAULTS_GENERIC
 		#endif		
-		#define DEFAULTS_MIDTBOT		
-		
-		#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)	
+		#define DEFAULTS_MIDTBOT	
 		
 		#define SERVO_PEN_PIN 					GPIO_NUM_27
 		
@@ -608,8 +600,7 @@
 			#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
 	#endif
 	
-	#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)	
-	
+		
 	//#define USE_PEN_SERVO
 	//#define SERVO_PEN_PIN 					GPIO_NUM_16
 	
@@ -720,9 +711,7 @@
 		
 		#ifndef SPINDLE_PWM_MIN_VALUE
 				#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
-		#endif
-		
-		#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)			
+		#endif	
 		
 		#define SERVO_Y_PIN 					GPIO_NUM_14
 		#define SERVO_Y_CHANNEL_NUM 	6
@@ -816,9 +805,7 @@
 		
 		#ifndef SPINDLE_PWM_MIN_VALUE
 				#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
-		#endif
-		
-		#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)			
+		#endif		
 		
 		// define Y and Z as servos
 		#define USE_SERVO_AXES
@@ -980,8 +967,6 @@
 			#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
 	#endif
 	
-	#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)		
-	
 	// Note: Only uncomment this if USE_SPINDLE_RELAY is commented out.
 	// Relay can be used for spindle or either coolant
 	//#define COOLANT_FLOOD_PIN 	GPIO_NUM_2
@@ -1082,9 +1067,7 @@
 	
 	#ifndef SPINDLE_PWM_MIN_VALUE
 			#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
-	#endif
-	
-	#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)		
+	#endif	
 	
 	// Note: Only uncomment this if USE_SPINDLE_RELAY is commented out.
 	// Relay can be used for Spindle or Coolant
@@ -1187,9 +1170,7 @@
 		
 		#ifndef SPINDLE_PWM_MIN_VALUE
 			#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
-		#endif
-		
-		#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)		
+		#endif		
 		
 		#define X_LIMIT_PIN      	GPIO_NUM_2
 		#define Y_LIMIT_PIN      	GPIO_NUM_4
@@ -1290,8 +1271,7 @@
 		#define SPINDLE_PWM_BIT_PRECISION 	8   // be sure to match this with SPINDLE_PWM_MAX_VALUE
 		#define SPINDLE_PWM_OFF_VALUE     	0
 		#define SPINDLE_PWM_MAX_VALUE     	255 // (2^SPINDLE_PWM_BIT_PRECISION)
-		#define SPINDLE_PWM_MIN_VALUE   		SPINDLE_PWM_OFF_VALUE   // Must be greater than zero.
-		#define SPINDLE_PWM_RANGE         	(SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)	
+		#define SPINDLE_PWM_MIN_VALUE   		SPINDLE_PWM_OFF_VALUE   // Must be greater than zero.		
 		
 		// defaults  ... <Idle|MPos:-497.000,-3.000,0.000,-3.000,-497.000,0.000|FS:0,0>
 		#ifdef DEFAULTS_GENERIC
diff --git a/Grbl_Esp32/gcode.cpp b/Grbl_Esp32/gcode.cpp
index 8afaf6a6..7128ca93 100644
--- a/Grbl_Esp32/gcode.cpp
+++ b/Grbl_Esp32/gcode.cpp
@@ -320,6 +320,9 @@ uint8_t gc_execute_line(char *line, uint8_t client)
 			case 3:
 			case 4:
 			case 5:
+				#ifndef SPINDLE_PWM_PIN
+					grbl_send(CLIENT_SERIAL, "[MSG:No spindle pin defined]\r\n");
+				#endif
 				word_bit = MODAL_GROUP_M7;
 				switch(int_value) {
 				case 3:
diff --git a/Grbl_Esp32/grbl.h b/Grbl_Esp32/grbl.h
index 3c3e1115..704fda23 100644
--- a/Grbl_Esp32/grbl.h
+++ b/Grbl_Esp32/grbl.h
@@ -20,7 +20,7 @@
 
 // Grbl versioning system
 #define GRBL_VERSION "1.1f"
-#define GRBL_VERSION_BUILD "20191008"
+#define GRBL_VERSION_BUILD "20191011"
 
 //#include <sdkconfig.h>
 #include <Arduino.h>
diff --git a/Grbl_Esp32/spindle_control.cpp b/Grbl_Esp32/spindle_control.cpp
index 1886983b..7af15de6 100644
--- a/Grbl_Esp32/spindle_control.cpp
+++ b/Grbl_Esp32/spindle_control.cpp
@@ -24,32 +24,47 @@ static float pwm_gradient; // Precalulated value to speed up rpm to PWM conversi
 
 void spindle_init()
 {
-    pwm_gradient = SPINDLE_PWM_RANGE/(settings.rpm_max-settings.rpm_min);
-	
-	// Use DIR and Enable if pins are defined
-	#ifdef SPINDLE_ENABLE_PIN
-		pinMode(SPINDLE_ENABLE_PIN, OUTPUT);
-	#endif
-	
-	#ifdef SPINDLE_DIR_PIN
-		pinMode(SPINDLE_DIR_PIN, OUTPUT);
-	#endif
-	
 	#ifdef SPINDLE_PWM_PIN
-    // use the LED control feature to setup PWM   https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/peripherals/ledc.html
-    ledcSetup(SPINDLE_PWM_CHANNEL, SPINDLE_PWM_BASE_FREQ, SPINDLE_PWM_BIT_PRECISION); // setup the channel
-    ledcAttachPin(SPINDLE_PWM_PIN, SPINDLE_PWM_CHANNEL); // attach the PWM to the pin
-	#endif
 	
-    // Start with spindle off off
-	  spindle_stop();
+		#ifdef INVERT_SPINDLE_PWM
+			grbl_send(CLIENT_SERIAL, "[MSG: INVERT_SPINDLE_PWM]\r\n");
+		#endif
+		
+		#ifdef INVERT_SPINDLE_ENABLE_PIN
+			grbl_send(CLIENT_SERIAL, "[MSG: INVERT_SPINDLE_ENABLE_PIN]\r\n");
+		#endif
+	
+		pwm_gradient = SPINDLE_PWM_RANGE/(settings.rpm_max-settings.rpm_min);
+		
+		// Use DIR and Enable if pins are defined
+		#ifdef SPINDLE_ENABLE_PIN
+			pinMode(SPINDLE_ENABLE_PIN, OUTPUT);
+		#endif
+		
+		#ifdef SPINDLE_DIR_PIN
+			pinMode(SPINDLE_DIR_PIN, OUTPUT);
+		#endif
+		
+		
+		// use the LED control feature to setup PWM   https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/peripherals/ledc.html
+		ledcSetup(SPINDLE_PWM_CHANNEL, SPINDLE_PWM_BASE_FREQ, SPINDLE_PWM_BIT_PRECISION); // setup the channel
+		ledcAttachPin(SPINDLE_PWM_PIN, SPINDLE_PWM_CHANNEL); // attach the PWM to the pin
+		
+		
+		// Start with spindle off off
+		 spindle_stop();
+	#endif
 }
 
 void spindle_stop()
 {		
   spindle_set_enable(false);
 	#ifdef SPINDLE_PWM_PIN
-		grbl_analogWrite(SPINDLE_PWM_CHANNEL, SPINDLE_PWM_OFF_VALUE);
+		#ifndef INVERT_SPINDLE_PWM
+			grbl_analogWrite(SPINDLE_PWM_CHANNEL, SPINDLE_PWM_OFF_VALUE);
+		#else
+			grbl_analogWrite(SPINDLE_PWM_CHANNEL, (1<<SPINDLE_PWM_BIT_PRECISION) - 1);
+		#endif
 	#endif
 }
 
@@ -58,95 +73,118 @@ uint8_t spindle_get_state()  // returns SPINDLE_STATE_DISABLE, SPINDLE_STATE_CW
   // TODO Update this when direction and enable pin are added
 	#ifndef SPINDLE_PWM_PIN
 		return(SPINDLE_STATE_DISABLE);
-	#endif
+	#else
 	
-	if (ledcRead(SPINDLE_PWM_CHANNEL) == 0) // Check the PWM value		
-		return(SPINDLE_STATE_DISABLE);
-	else
-	{
-		#ifdef SPINDLE_DIR_PIN			
-			if (digitalRead(SPINDLE_DIR_PIN))
-				return (SPINDLE_STATE_CW);
-			else
-				return(SPINDLE_STATE_CCW);
-		#else
-			return(SPINDLE_STATE_CW);
-		#endif		
-	}
+		if (ledcRead(SPINDLE_PWM_CHANNEL) == 0) // Check the PWM value		
+			return(SPINDLE_STATE_DISABLE);
+		else
+		{
+			#ifdef SPINDLE_DIR_PIN			
+				if (digitalRead(SPINDLE_DIR_PIN))
+					return (SPINDLE_STATE_CW);
+				else
+					return(SPINDLE_STATE_CCW);
+			#else
+				return(SPINDLE_STATE_CW);
+			#endif		
+		}
+	#endif
 }
 
 void spindle_set_speed(uint32_t pwm_value)
 {	
 	#ifndef SPINDLE_PWM_PIN
 		return;
+	#else
+		#ifndef SPINDLE_ENABLE_OFF_WITH_ZERO_SPEED
+			spindle_set_enable(true);
+		#else
+			spindle_set_enable(pwm_value != 0);
+		#endif
+		
+		#ifndef INVERT_SPINDLE_PWM
+			grbl_analogWrite(SPINDLE_PWM_CHANNEL, pwm_value);			
+		#else
+			if (pwm_value == 0) {
+				grbl_analogWrite(SPINDLE_PWM_CHANNEL, (1<<SPINDLE_PWM_BIT_PRECISION));
+			}
+			else {
+				grbl_analogWrite(SPINDLE_PWM_CHANNEL, (1<<SPINDLE_PWM_BIT_PRECISION) - pwm_value - 1);
+			}			
+		#endif
+		
 	#endif
 
-	#ifndef SPINDLE_ENABLE_OFF_WITH_ZERO_SPEED
-		spindle_set_enable(true);
-	#else
-		spindle_set_enable(pwm_value != 0);
-	#endif
-	grbl_analogWrite(SPINDLE_PWM_CHANNEL, pwm_value);
+	
 }
 
 // Called by spindle_set_state() and step segment generator. Keep routine small and efficient.
 uint32_t spindle_compute_pwm_value(float rpm)
 {
-  uint32_t pwm_value;
-  rpm *= (0.010*sys.spindle_speed_ovr); // Scale by spindle speed override value.
-  // Calculate PWM register value based on rpm max/min settings and programmed rpm.
-  if ((settings.rpm_min >= settings.rpm_max) || (rpm >= settings.rpm_max)) {
-    // No PWM range possible. Set simple on/off spindle control pin state.
-    sys.spindle_speed = settings.rpm_max;
-    pwm_value = SPINDLE_PWM_MAX_VALUE;
-  } else if (rpm <= settings.rpm_min) {
-    if (rpm == 0.0) { // S0 disables spindle
-      sys.spindle_speed = 0.0;
-      pwm_value = SPINDLE_PWM_OFF_VALUE;
-    } else { // Set minimum PWM output
-      sys.spindle_speed = settings.rpm_min;
-      pwm_value = SPINDLE_PWM_MIN_VALUE;
-    }
-  } else {
-    // Compute intermediate PWM value with linear spindle speed model.
-    // NOTE: A nonlinear model could be installed here, if required, but keep it VERY light-weight.
-    sys.spindle_speed = rpm;
-    pwm_value = floor((rpm-settings.rpm_min)*pwm_gradient) + SPINDLE_PWM_MIN_VALUE;
-  }
-  return(pwm_value);
-
+	#ifdef SPINDLE_PWM_PIN
+		uint32_t pwm_value;
+		rpm *= (0.010*sys.spindle_speed_ovr); // Scale by spindle speed override value.
+		// Calculate PWM register value based on rpm max/min settings and programmed rpm.
+		if ((settings.rpm_min >= settings.rpm_max) || (rpm >= settings.rpm_max)) {
+		// No PWM range possible. Set simple on/off spindle control pin state.
+			sys.spindle_speed = settings.rpm_max;
+			pwm_value = SPINDLE_PWM_MAX_VALUE;
+		} else if (rpm <= settings.rpm_min) {
+			if (rpm == 0.0) { // S0 disables spindle
+				sys.spindle_speed = 0.0;
+				pwm_value = SPINDLE_PWM_OFF_VALUE;
+			} else { // Set minimum PWM output
+				sys.spindle_speed = settings.rpm_min;
+			pwm_value = SPINDLE_PWM_MIN_VALUE;
+			}
+		} else {
+			// Compute intermediate PWM value with linear spindle speed model.
+			// NOTE: A nonlinear model could be installed here, if required, but keep it VERY light-weight.
+			sys.spindle_speed = rpm;
+			pwm_value = floor((rpm-settings.rpm_min)*pwm_gradient) + SPINDLE_PWM_MIN_VALUE;
+		}		
+		
+		return(pwm_value);
+	#else
+		return(0); // no SPINDLE_PWM_PIN
+	#endif
 }
 
 
 void spindle_set_state(uint8_t state, float rpm)
 {
-  if (sys.abort) { return; } // Block during abort.
-  if (state == SPINDLE_DISABLE) { // Halt or set spindle direction and rpm.    
-    sys.spindle_speed = 0.0;    
-    spindle_stop();  
-  } else {
-  
-    // TODO ESP32 Enable and direction control
-		#ifdef SPINDLE_DIR_PIN		
-      digitalWrite(SPINDLE_DIR_PIN, state == SPINDLE_ENABLE_CW);    
-		#endif  
-    
-      // NOTE: Assumes all calls to this function is when Grbl is not moving or must remain off.
-      if (settings.flags & BITFLAG_LASER_MODE) { 
-        if (state == SPINDLE_ENABLE_CCW) { rpm = 0.0; } // TODO: May need to be rpm_min*(100/MAX_SPINDLE_SPEED_OVERRIDE);
-      }
-						
-      spindle_set_speed(spindle_compute_pwm_value(rpm));     
-  }  
-  sys.report_ovr_counter = 0; // Set to report change immediately
+	#ifdef SPINDLE_PWM_PIN
+	  if (sys.abort) { return; } // Block during abort.
+	  if (state == SPINDLE_DISABLE) { // Halt or set spindle direction and rpm.    
+		sys.spindle_speed = 0.0;    
+		spindle_stop();  
+	  } else {
+	  
+		// TODO ESP32 Enable and direction control
+			#ifdef SPINDLE_DIR_PIN		
+		  digitalWrite(SPINDLE_DIR_PIN, state == SPINDLE_ENABLE_CW);    
+			#endif  
+		
+		  // NOTE: Assumes all calls to this function is when Grbl is not moving or must remain off.
+		  if (settings.flags & BITFLAG_LASER_MODE) { 
+			if (state == SPINDLE_ENABLE_CCW) { rpm = 0.0; } // TODO: May need to be rpm_min*(100/MAX_SPINDLE_SPEED_OVERRIDE);
+		  }
+							
+		  spindle_set_speed(spindle_compute_pwm_value(rpm));     
+	  }  
+	  sys.report_ovr_counter = 0; // Set to report change immediately
+	#endif
 }
 
 
 void spindle_sync(uint8_t state, float rpm)
 {
-	if (sys.state == STATE_CHECK_MODE) { return; }
-  protocol_buffer_synchronize(); // Empty planner buffer to ensure spindle is set when programmed.
-  spindle_set_state(state,rpm);
+	if (sys.state == STATE_CHECK_MODE) { 
+		return;
+	}
+	
+	protocol_buffer_synchronize(); // Empty planner buffer to ensure spindle is set when programmed.
+	spindle_set_state(state,rpm);
 }
 
 
@@ -154,7 +192,7 @@ void grbl_analogWrite(uint8_t chan, uint32_t duty)
 {
 	if (ledcRead(chan) != duty) // reduce unnecessary calls to ledcWrite()
 	{
-		// grbl_sendf(CLIENT_SERIAL, "[MSG: Spindle duty: %d of %d]\r\n", duty, SPINDLE_PWM_MAX_VALUE); // debug statement
+		
 		ledcWrite(chan, duty);
 	}
 }
diff --git a/Grbl_Esp32/spindle_control.h b/Grbl_Esp32/spindle_control.h
index 81df7a7e..13a1b433 100644
--- a/Grbl_Esp32/spindle_control.h
+++ b/Grbl_Esp32/spindle_control.h
@@ -22,6 +22,8 @@
   #define spindle_control_h
   
   #include "grbl.h"
+  
+#define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)
 
 #define SPINDLE_NO_SYNC false
 #define SPINDLE_FORCE_SYNC true
diff --git a/Grbl_Esp32/stepper.cpp b/Grbl_Esp32/stepper.cpp
index de9c2da0..ef89c7e0 100644
--- a/Grbl_Esp32/stepper.cpp
+++ b/Grbl_Esp32/stepper.cpp
@@ -282,11 +282,11 @@ void IRAM_ATTR onStepperDriverTimer(void *para)  // ISR It is time to take a ste
 		} else {
 			// Segment buffer empty. Shutdown.
 			st_go_idle();
-#ifdef VARIABLE_SPINDLE
+#if ( (defined VARIABLE_SPINDLE) && (defined SPINDLE_PWM_PIN) )
 			if (!(sys.state & STATE_JOG)) {  // added to prevent ... jog after probing crash
 				// Ensure pwm is set properly upon completion of rate-controlled motion.
-				if (st.exec_block->is_pwm_rate_adjusted) {
-					spindle_set_speed(SPINDLE_PWM_OFF_VALUE);
+				if (st.exec_block->is_pwm_rate_adjusted) {					
+					spindle_set_speed(SPINDLE_PWM_OFF_VALUE);					
 				}
 			}		
 
@@ -1316,7 +1316,10 @@ void st_prep_buffer()
 				prep.current_spindle_pwm = spindle_compute_pwm_value(rpm);
 			} else {
 				sys.spindle_speed = 0.0;
-				prep.current_spindle_pwm = SPINDLE_PWM_OFF_VALUE;
+				#if ( (defined VARIABLE_SPINDLE) && (defined SPINDLE_PWM_PIN) )
+					prep.current_spindle_pwm = SPINDLE_PWM_OFF_VALUE;
+				#endif
+				
 			}
 			bit_false(sys.step_control,STEP_CONTROL_UPDATE_SPINDLE_PWM);
 		}