diff --git a/module04/ex02/header.h b/module04/ex02/header.h
index b4d8b56..e7a7ea8 100644
--- a/module04/ex02/header.h
+++ b/module04/ex02/header.h
@@ -14,7 +14,17 @@
 // PROTOTYPES
 //
 // main.c
-void blink_led_1();
-void vary_duty();
+void print_binary(int value);
+void increment_int();
+void decrement_int();
+void increment_led();
+void decrement_led();
+void on_press(int bit, void (*action)(void));
+
+//
+// MACROS
+//
+#define MAX			15
+#define MIN			0
 
 #endif // HEADER_H
\ No newline at end of file
diff --git a/module04/ex02/main.c b/module04/ex02/main.c
index e3a85c3..478cecd 100644
--- a/module04/ex02/main.c
+++ b/module04/ex02/main.c
@@ -1,10 +1,27 @@
 #include "header.h"
 
-typedef struct {
-    int *value;
-    int max;
-	int min;
-} IncrementParams;
+// ALTERNATE FUNCTIONS :
+//   Table 14-9 : port D alternate functions
+//   BUTTON1 SW1 PD2 :
+//    -> INT0 (External Interrupt 0 Input)
+//    -> PCINT18 (Pin Change Interrupt 18)
+//   BUTTON2 SW2 PD4 :
+//    -> XCK (USART External Clock Input/Output)
+//    -> T0 (Timer/Counter 0 External Counter Input)
+//    -> PCINT20 (Pin Change Interrupt 20)
+// EXTERNAL INTERRUPTS GROUP :
+//   13.2.4 : pin change interrupt controle register (PCICR)
+//    -> bit PCIE2 for PCINT[23:16] (PCI2 Interrupt Vector)
+//       PCMSK2 to enable each pin
+// INTERRUPT VECTORS NAME :
+//   Table 12-6 : interrupts vectors
+//    -> PCINT2_vect
+// ENABLE PIN CHANGE INTERRUPT :
+//   13.2.6 : PCMSK2 – Pin Change Mask Register 2
+//    -> (1 << PCINT20) | (1 << PCINT18)
+
+volatile uint8_t prevPIND;							// Store previous state of PIND
+volatile uint8_t value = 0;
 
 void print_binary(int value) {
 	int mask_3 = 0b1000;
@@ -13,33 +30,33 @@ void print_binary(int value) {
 	PORTB = (value & 0b111) + bit_at_4;
 }
 
-void increment_int(IncrementParams *params) {
-	int *value = params->value;
-	int max = params->max;
-	*value = (*value >= max) ? max : ++(*value);
+void increment_int() {
+	// int *value = params->value;
+	// int max = params->max;
+	value = (value >= MAX) ? MAX : ++value;
 }
 
-void decrement_int(IncrementParams *params) {
-	int *value = params->value;
-	int min = params->min;
-    *value = (*value <= min) ? min : --(*value);
+void decrement_int() {
+	// int *value = params->value;
+	// int min = params->min;
+    value = (value <= MIN) ? MIN : --value;
 }
 
-void increment_led(void *param) {
-	IncrementParams *params = (IncrementParams *)param;
-	increment_int(params);
-	print_binary(*(params->value));
+void increment_led() {
+	// IncrementParams *params = (IncrementParams *)param;
+	increment_int();
+	print_binary(value);
 }
 
-void decrement_led(void *param) {
-	IncrementParams *params = (IncrementParams *)param;
-	decrement_int(params);
-	print_binary(*(params->value));
+void decrement_led() {
+	// IncrementParams *params = (IncrementParams *)param;
+	decrement_int();
+	print_binary(value);
 }
 
-void on_press(int bit, void (*action)(void*), void *params) {
+void on_press(int bit, void (*action)(void)) {
 	if ((TEST(PIND, bit)) == 0) {
-	    action(params);
+	    action();
 	    _delay_ms(20);
 	    while ((TEST(PIND, bit)) == 0) {
 	        continue;
@@ -48,7 +65,7 @@ void on_press(int bit, void (*action)(void*), void *params) {
 	}
 }
 
-// write a program that increments and decrements a binary number using the buttons, and displays the result on the LEDs
+// write a program that incr/decr-ements a number with the buttons, using interrupts, empty infinite loop, and displays the result on LEDs in binary
 int main() {
 	MODE_OUTPUT(LED1);
 	MODE_OUTPUT(LED2);
@@ -56,17 +73,28 @@ int main() {
 	MODE_OUTPUT(LED4);
 	MODE_INPUT(BUTTON1);
 	MODE_INPUT(BUTTON2);
-	
-	int value = 0;
-    int max = 15;
-	int min = 0;
-    IncrementParams params = {&value, max};
+	PULLUP_ON(BUTTON1);
+	PULLUP_ON(BUTTON2);
 
-	while(1) {
-		on_press(SW1, increment_led, &params);
-		on_press(SW2, decrement_led, &params);
+	SREG |= ENABLE_GLOBAL_INTERRUPT;
+
+	PCICR = (1 << PCIE2);							// 13.2.4 : enable pin change interrupt, bit PCIE2 for PCINT[23:16], (Table 14-9 : alternates : PD2 - PCINT18, PD4 - PCINT20)
+	PCMSK2 = (1 << PCINT20) | (1 << PCINT18);		// 13.2.6 : enable individual pin chang interrupt
+
+	prevPIND = PIND;
+
+	while(1);
+}
+
+ISR(PCINT2_vect) {
+    uint8_t currentPIND = PIND;						// Read the current state of Port D
+    uint8_t changedPins = currentPIND ^ prevPIND;	// Find changed bits
+
+	if (!TEST(changedPins, SW1)) {
+		on_press(SW1, increment_led);
 	}
-}
-
-ISR(TIMER0_COMPA_vect) {
+	if (!TEST(changedPins, SW1)) {
+		on_press(SW2, decrement_led);
+	}
+	prevPIND = currentPIND;
 }