diff --git a/.vscode/settings.json b/.vscode/settings.json
index af4ab8e..01550e4 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -2,6 +2,9 @@
   "files.associations": {
     "io.h": "c",
     "delay.h": "c",
-    "interrupt.h": "c"
+    "interrupt.h": "c",
+    "timer.h": "c",
+    "usart.h": "c",
+    "utils.h": "c"
   }
 }
diff --git a/module02/ex00/bitmanip.h b/module02/ex00/bitmanip.h
index 5e36761..4df44d1 100644
--- a/module02/ex00/bitmanip.h
+++ b/module02/ex00/bitmanip.h
@@ -14,8 +14,14 @@
 #define ARG_2(v1, v2)			v2
 #define GET_PORT(args)			ARG_1 args
 #define GET_BIT(args)			ARG_2 args
+// // version with "LED1 B, D1" without parenthesis
+// #define ARG_1(v1, ...)			v1
+// #define ARG_2(v1, v2, ...)		v2
+// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
+// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
 
 // Actions on elements
+// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
 #define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
 #define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
 #define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
diff --git a/module02/ex00/main.c b/module02/ex00/main.c
index 8cddfff..4185c9a 100644
--- a/module02/ex00/main.c
+++ b/module02/ex00/main.c
@@ -2,63 +2,8 @@
 #include <util/delay.h>
 #include <avr/interrupt.h>
 
-// mathematics
-#define DIV_ROUND_CLOSEST(n, d) ((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d)))
-
-// stringify
-#define STRINGIFY_HELPER(x)		#x
-#define STRINGIFY(x)			STRINGIFY_HELPER(x)
-
-// concatenate
-#define CONCAT_HELPER(x, y)		x ## y
-#define CONCAT(x, y)			CONCAT_HELPER(x, y)
-
-// get argument
-#define ARG_1(v1, v2)			v1
-#define ARG_2(v1, v2)			v2
-#define GET_PORT(args)			ARG_1 args
-#define GET_BIT(args)			ARG_2 args
-// // version with "LED1 B, D1" without parenthesis
-// #define ARG_1(v1, ...)			v1
-// #define ARG_2(v1, v2, ...)		v2
-// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
-// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
-
-// actions on registers
-#define SET(register, bit)		register |= 1 << bit
-#define CLEAR(register, bit)	register &= ~(1 << bit)
-#define TEST(register, bit)		(register & 1 << bit)
-#define TOGGLE(register, bit)	register ^= 1 << bit
-
-// actions on elements
-#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
-#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
-#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
-#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
-#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
-#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
-#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)
-
-// bits
-#define D1	0
-#define D2	1
-#define D3	2
-#define D4	4
-#define SW1	2
-#define SW2	4
-
-// elements (port, bit)
-// #define LED1	B, D1
-#define LED1	(B, D1)
-#define LED2	(B, D2)
-#define LED3	(B, D3)
-#define LED4	(B, D4)
-#define BUTTON1	(D, SW1)
-#define BUTTON2	(D, SW2)
+#include "utils.h"
+#include "bitmanip.h"
 
 // USART
 // Table 20-1 : Baud Rate Calculation
@@ -104,7 +49,7 @@ void uart_tx(char c) {
 	UDR0 = (unsigned char) c;													// 20.11.1 : Put data into buffer, UDRn – USART I/O Data Register (read and write)
 }
 
-// write Z on serial port, at a !Hz frequency
+// write Z on serial port, at a 1Hz frequency
 // `screen /dev/ttyUSB0 115200`
 int main() {
 	uart_init();
diff --git a/module02/ex00/timer.h b/module02/ex00/timer.h
deleted file mode 100644
index 3cb618e..0000000
--- a/module02/ex00/timer.h
+++ /dev/null
@@ -1,15 +0,0 @@
-#ifndef TIMER_H
-#define TIMER_H
-
-#define PRESCALE_VALUE				1024		// can be 1, 8, 64, 256, 1024
-// table 16-5 : prescale sets
-#define PRESCALE_SET(value)  \
-									((value) == 1   ? (0<<CS12 | 0<<CS11 | 1<<CS10) : \
-									 (value) == 8   ? (0<<CS12 | 1<<CS11 | 0<<CS10) : \
-									 (value) == 64  ? (0<<CS12 | 1<<CS11 | 1<<CS10) : \
-									 (value) == 256 ? (1<<CS12 | 0<<CS11 | 0<<CS10) : \
-									 (value) == 1024? (1<<CS12 | 0<<CS11 | 1<<CS10) : \
-													  (0<<CS12 | 0<<CS11 | 0<<CS10))
-#define TIME_MS(ms)					(((F_CPU / PRESCALE_VALUE) * ms) / 1000)
-
-#endif // TIMER_H
\ No newline at end of file
diff --git a/module02/ex00/utils.h b/module02/ex00/utils.h
index b17bc0f..5c22e0b 100644
--- a/module02/ex00/utils.h
+++ b/module02/ex00/utils.h
@@ -11,5 +11,6 @@
 
 // mathematics
 #define PERCENT(percent, total)		(((float)percent / 100) * total)
+#define DIV_ROUND_CLOSEST(n, d)		((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d)))
 
 #endif // UTILS_H
\ No newline at end of file
diff --git a/module02/ex01/bitmanip.h b/module02/ex01/bitmanip.h
new file mode 100644
index 0000000..4df44d1
--- /dev/null
+++ b/module02/ex01/bitmanip.h
@@ -0,0 +1,53 @@
+#ifndef BITMANIP_H
+#define BITMANIP_H
+
+#include "utils.h"
+
+// Bit operations on registers
+#define SET(register, bit)		(register |= (1 << (bit)))
+#define CLEAR(register, bit)	(register &= ~(1 << (bit)))
+#define TEST(register, bit)		(register & (1 << (bit)))
+#define TOGGLE(register, bit)	(register ^= (1 << (bit)))
+
+// Get arguments from tuple-like definitions
+#define ARG_1(v1, v2)			v1
+#define ARG_2(v1, v2)			v2
+#define GET_PORT(args)			ARG_1 args
+#define GET_BIT(args)			ARG_2 args
+// // version with "LED1 B, D1" without parenthesis
+// #define ARG_1(v1, ...)			v1
+// #define ARG_2(v1, v2, ...)		v2
+// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
+// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
+
+// Actions on elements
+// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
+#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+
+#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
+#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
+#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
+#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
+#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
+#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)
+
+// Bit definitions
+#define D1 0
+#define D2 1
+#define D3 2
+#define D4 4
+#define SW1 2
+#define SW2 4
+
+// Elements (port, bit)
+#define LED1	(B, D1)
+#define LED2	(B, D2)
+#define LED3	(B, D3)
+#define LED4	(B, D4)
+#define BUTTON1	(D, SW1)
+#define BUTTON2	(D, SW2)
+
+#endif // BITMANIP_H
\ No newline at end of file
diff --git a/module02/ex01/interrupt.h b/module02/ex01/interrupt.h
new file mode 100644
index 0000000..dccc1c5
--- /dev/null
+++ b/module02/ex01/interrupt.h
@@ -0,0 +1,8 @@
+#ifndef INTERRUPT_H
+#define INTERRUPT_H
+
+// 7.3.1 : SREG – AVR Status Register
+#define ENABLE_GLOBAL_INTERRUPT		(1<<7)
+#define DISABLE_GLOBAL_INTERRUPT	(0<<7)
+
+#endif // INTERRUPT_H
\ No newline at end of file
diff --git a/module02/ex01/main.c b/module02/ex01/main.c
index 9f9244f..54ca8b1 100644
--- a/module02/ex01/main.c
+++ b/module02/ex01/main.c
@@ -2,120 +2,24 @@
 #include <util/delay.h>
 #include <avr/interrupt.h>
 
-// mathematics 
-#define DIV_ROUND_CLOSEST(n, d)	((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d))) // https://stackoverflow.com/a/18067292
 
-// stringify
-#define STRINGIFY_HELPER(x)		#x
-#define STRINGIFY(x)			STRINGIFY_HELPER(x)
-
-// concatenate
-#define CONCAT_HELPER(x, y)		x ## y
-#define CONCAT(x, y)			CONCAT_HELPER(x, y)
-
-// get argument
-#define ARG_1(v1, v2)			v1
-#define ARG_2(v1, v2)			v2
-#define GET_PORT(args)			ARG_1 args
-#define GET_BIT(args)			ARG_2 args
-// // version with "LED1 B, D1" without parenthesis
-// #define ARG_1(v1, ...)			v1
-// #define ARG_2(v1, v2, ...)		v2
-// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
-// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
-
-// actions on registers
-#define SET(register, bit)		register |= 1 << bit
-#define CLEAR(register, bit)	register &= ~(1 << bit)
-#define TEST(register, bit)		(register & 1 << bit)
-#define TOGGLE(register, bit)	register ^= 1 << bit
-
-// actions on elements
-#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
-#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
-#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
-#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
-#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
-#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
-#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)
-
-// bits
-#define D1	0
-#define D2	1
-#define D3	2
-#define D4	4
-#define SW1	2
-#define SW2	4
-
-// elements (port, bit)
-// #define LED1	B, D1
-#define LED1	(B, D1)
-#define LED2	(B, D2)
-#define LED3	(B, D3)
-#define LED4	(B, D4)
-#define BUTTON1	(D, SW1)
-#define BUTTON2	(D, SW2)
-
-// USART
-// Table 20-1 : Baud Rate Calculation
-#define USART_BAUDRATE					115200
-#define BAUD_PRESCALER					(DIV_ROUND_CLOSEST(F_CPU, (16 * USART_BAUDRATE)) - 1)
-// Table 20-8 : Mode Selection (USART Mode SELect)
-#define ASYNCHRONOUS					(0<<UMSEL01 | 0<<UMSEL00)
-#define SYNCHRONOUS						(0<<UMSEL01 | 1<<UMSEL00)
-// Table 20-9 : Parity Bit Selection (USART Parity Mode)
-#define PARITY_DISABLED					(0<<UPM01 | 0<<UPM00)
-#define PARITY_EVEN						(1<<UPM01 | 0<<UPM00)
-#define PARITY_ODD						(1<<UPM01 | 1<<UPM00)
-// Table 20-10 : Stop Bit Selection (USART Stop Bit Select)
-#define STOP_ONE_BIT					(0<<USBS0)
-#define STOP_TWO_BIT					(1<<USBS0)
-// Table 20-11 : Data Bit Selection (USART Character SiZe)
-#define DATA_FIVE_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 0<<UCSZ00)
-#define DATA_SIX_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 1<<UCSZ00)
-#define DATA_SEVEN_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 0<<UCSZ00)
-#define DATA_EIGHT_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
-#define DATA_NINE_BIT					(1<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
-// 20.11.3 : USART Control and Status Register B (UCSRnB)
-#define RECEIVER_DISABLED				(0<<RXEN0)
-#define RECEIVER_ENABLED				(1<<RXEN0)
-#define TRANSMITTER_DISABLED			(0<<TXEN0)
-#define TRANSMITTER_ENABLED				(1<<TXEN0)
+#include "utils.h"
+#include "bitmanip.h"
+#include "timer.h"
+#include "usart.h"
+#include "interrupt.h"
 
 // TIMER
 #define PERIOD							2000
-#define TIME_MS(ms)						(((F_CPU / PRESCALE_VALUE) * ms) / 1000)
 #define PRESCALE_VALUE					1024		// can be 1, 8, 64, 256, 1024
-// table 16-5 : prescale sets
-#define PRESCALE_SET(value)  \
-										((value) == 1   ? (0<<CS12 | 0<<CS11 | 1<<CS10) : \
-										 (value) == 8   ? (0<<CS12 | 1<<CS11 | 0<<CS10) : \
-										 (value) == 64  ? (0<<CS12 | 1<<CS11 | 1<<CS10) : \
-										 (value) == 256 ? (1<<CS12 | 0<<CS11 | 0<<CS10) : \
-										 (value) == 1024? (1<<CS12 | 0<<CS11 | 1<<CS10) : \
-														  (0<<CS12 | 0<<CS11 | 0<<CS10))
-// Table 16-4 : Waveform Generation Mode Bit Description
-#define CTC_TOP_OCR1A_IN_TCCR1B			(0<<WGM13 | 1<<WGM12)
-#define CTC_TOP_OCR1A_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
-#define CTC_TOP_ICR1_IN_TCCR1B			(1<<WGM13 | 1<<WGM12)
-#define CTC_TOP_ICR1_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
-#define FAST_PWM_TOP_OCR1A_IN_TCCR1B	(1<<WGM13 | 1<<WGM12)
-#define FAST_PWM_TOP_OCR1A_IN_TCCR1A							(1<<WGM11 | 1<<WGM10)
-#define FAST_PWM_TOP_ICR1_IN_TCCR1B		(1<<WGM13 | 1<<WGM12)
-#define FAST_PWM_TOP_ICR1_IN_TCCR1A								(1<<WGM11 | 0<<WGM10)
-// 16.11.8 : Timer/Counter1 Interrupt Mask Register
-#define INTERRUPT_ENABLE_CHANNEL_A		(1 << OCIE1A)
-#define INTERRUPT_DISABLE_CHANNEL_A		(0 << OCIE1A)
+// USART
+#define USART_BAUDRATE					115200		// Table 20-1 : Baud Rate Calculation
 
 // END MACROS
 
 void uart_init() {
-	UBRR0H = (unsigned char) (BAUD_PRESCALER >> 8);								// 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
-	UBRR0L = (unsigned char) BAUD_PRESCALER;
+	UBRR0H = (unsigned char) (BAUD_PRESCALER(USART_BAUDRATE) >> 8);								// 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
+	UBRR0L = (unsigned char) BAUD_PRESCALER(USART_BAUDRATE);
 
 	UCSR0C |= ASYNCHRONOUS | PARITY_DISABLED | STOP_ONE_BIT | DATA_EIGHT_BIT;	// 20.11.4 : set Frame Format
 	
@@ -142,10 +46,11 @@ int main() {
 	TCCR1A |= CTC_TOP_OCR1A_IN_TCCR1A;				// Table 16-4 : set timer in CTC (Clear Time on Compare) mode
 	TCCR1B |= CTC_TOP_OCR1A_IN_TCCR1B;
 
-	sei();											// enable global interrupts (https://www.nongnu.org/avr-libc/user-manual/group__avr__interrupts.html#gaad5ebd34cb344c26ac87594f79b06b73)
+	SREG |= ENABLE_GLOBAL_INTERRUPT;				// 7.3.1 : Status Register, bit 7 : I – Global Interrupt Enable
+
 	TIMSK1 |= INTERRUPT_ENABLE_CHANNEL_A;			// 16.11.8 : enables the Timer1 Compare Match A interrupt, this makes the MCU react when OCR1A == TCNT1 by calling TIMER1_COMPA_vect
 
-	OCR1A = TIME_MS(PERIOD);						// Table 16-4 : set CTC compare value on channel A, the counter is cleared to zero when the counter value (TCNT1) matches the OCR1A register
+	OCR1A = TIME_MS(PERIOD, PRESCALE_VALUE);		// Table 16-4 : set CTC compare value on channel A, the counter is cleared to zero when the counter value (TCNT1) matches the OCR1A register
 
 	TCCR1B |= (PRESCALE_SET(PRESCALE_VALUE));		// 16.4 : set timer according to prescale value, in register TCCR1B, table 16-5 : prescale sets
 
diff --git a/module02/ex01/timer.h b/module02/ex01/timer.h
new file mode 100644
index 0000000..2493232
--- /dev/null
+++ b/module02/ex01/timer.h
@@ -0,0 +1,27 @@
+#ifndef TIMER_H
+#define TIMER_H
+
+// table 16-5 : prescale sets
+#define PRESCALE_SET(value)  \
+									((value) == 1   ? (0<<CS12 | 0<<CS11 | 1<<CS10) : \
+									 (value) == 8   ? (0<<CS12 | 1<<CS11 | 0<<CS10) : \
+									 (value) == 64  ? (0<<CS12 | 1<<CS11 | 1<<CS10) : \
+									 (value) == 256 ? (1<<CS12 | 0<<CS11 | 0<<CS10) : \
+									 (value) == 1024? (1<<CS12 | 0<<CS11 | 1<<CS10) : \
+													  (0<<CS12 | 0<<CS11 | 0<<CS10))
+#define TIME_MS(ms, prescale_value)	(((F_CPU / prescale_value) * ms) / 1000)
+
+// Table 16-4 : Waveform Generation Mode Bit Description
+#define CTC_TOP_OCR1A_IN_TCCR1B			(0<<WGM13 | 1<<WGM12)
+#define CTC_TOP_OCR1A_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
+#define CTC_TOP_ICR1_IN_TCCR1B			(1<<WGM13 | 1<<WGM12)
+#define CTC_TOP_ICR1_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
+#define FAST_PWM_TOP_OCR1A_IN_TCCR1B	(1<<WGM13 | 1<<WGM12)
+#define FAST_PWM_TOP_OCR1A_IN_TCCR1A							(1<<WGM11 | 1<<WGM10)
+#define FAST_PWM_TOP_ICR1_IN_TCCR1B		(1<<WGM13 | 1<<WGM12)
+#define FAST_PWM_TOP_ICR1_IN_TCCR1A								(1<<WGM11 | 0<<WGM10)
+// 16.11.8 : Timer/Counter1 Interrupt Mask Register
+#define INTERRUPT_ENABLE_CHANNEL_A		(1 << OCIE1A)
+#define INTERRUPT_DISABLE_CHANNEL_A		(0 << OCIE1A)
+
+#endif // TIMER_H
\ No newline at end of file
diff --git a/module02/ex01/usart.h b/module02/ex01/usart.h
new file mode 100644
index 0000000..88d7fd0
--- /dev/null
+++ b/module02/ex01/usart.h
@@ -0,0 +1,27 @@
+#ifndef USART_H
+#define USART_H
+
+#define BAUD_PRESCALER(usart_baudrate)	(DIV_ROUND_CLOSEST(F_CPU, (16 * usart_baudrate)) - 1)
+// Table 20-8 : Mode Selection (USART Mode SELect)
+#define ASYNCHRONOUS					(0<<UMSEL01 | 0<<UMSEL00)
+#define SYNCHRONOUS						(0<<UMSEL01 | 1<<UMSEL00)
+// Table 20-9 : Parity Bit Selection (USART Parity Mode)
+#define PARITY_DISABLED					(0<<UPM01 | 0<<UPM00)
+#define PARITY_EVEN						(1<<UPM01 | 0<<UPM00)
+#define PARITY_ODD						(1<<UPM01 | 1<<UPM00)
+// Table 20-10 : Stop Bit Selection (USART Stop Bit Select)
+#define STOP_ONE_BIT					(0<<USBS0)
+#define STOP_TWO_BIT					(1<<USBS0)
+// Table 20-11 : Data Bit Selection (USART Character SiZe)
+#define DATA_FIVE_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 0<<UCSZ00)
+#define DATA_SIX_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 1<<UCSZ00)
+#define DATA_SEVEN_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 0<<UCSZ00)
+#define DATA_EIGHT_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
+#define DATA_NINE_BIT					(1<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
+// 20.11.3 : USART Control and Status Register B (UCSRnB)
+#define RECEIVER_DISABLED				(0<<RXEN0)
+#define RECEIVER_ENABLED				(1<<RXEN0)
+#define TRANSMITTER_DISABLED			(0<<TXEN0)
+#define TRANSMITTER_ENABLED				(1<<TXEN0)
+
+#endif // USART_H
\ No newline at end of file
diff --git a/module02/ex01/utils.h b/module02/ex01/utils.h
new file mode 100644
index 0000000..5c22e0b
--- /dev/null
+++ b/module02/ex01/utils.h
@@ -0,0 +1,16 @@
+#ifndef UTILS_H
+#define UTILS_H
+
+// stringify
+#define STRINGIFY_HELPER(x)			#x
+#define STRINGIFY(x)				STRINGIFY_HELPER(x)
+
+// concatenate
+#define CONCAT_HELPER(x, y)			x ## y
+#define CONCAT(x, y)				CONCAT_HELPER(x, y)
+
+// mathematics
+#define PERCENT(percent, total)		(((float)percent / 100) * total)
+#define DIV_ROUND_CLOSEST(n, d)		((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d)))
+
+#endif // UTILS_H
\ No newline at end of file
diff --git a/module02/ex02/bitmanip.h b/module02/ex02/bitmanip.h
new file mode 100644
index 0000000..4df44d1
--- /dev/null
+++ b/module02/ex02/bitmanip.h
@@ -0,0 +1,53 @@
+#ifndef BITMANIP_H
+#define BITMANIP_H
+
+#include "utils.h"
+
+// Bit operations on registers
+#define SET(register, bit)		(register |= (1 << (bit)))
+#define CLEAR(register, bit)	(register &= ~(1 << (bit)))
+#define TEST(register, bit)		(register & (1 << (bit)))
+#define TOGGLE(register, bit)	(register ^= (1 << (bit)))
+
+// Get arguments from tuple-like definitions
+#define ARG_1(v1, v2)			v1
+#define ARG_2(v1, v2)			v2
+#define GET_PORT(args)			ARG_1 args
+#define GET_BIT(args)			ARG_2 args
+// // version with "LED1 B, D1" without parenthesis
+// #define ARG_1(v1, ...)			v1
+// #define ARG_2(v1, v2, ...)		v2
+// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
+// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
+
+// Actions on elements
+// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
+#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+
+#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
+#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
+#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
+#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
+#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
+#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)
+
+// Bit definitions
+#define D1 0
+#define D2 1
+#define D3 2
+#define D4 4
+#define SW1 2
+#define SW2 4
+
+// Elements (port, bit)
+#define LED1	(B, D1)
+#define LED2	(B, D2)
+#define LED3	(B, D3)
+#define LED4	(B, D4)
+#define BUTTON1	(D, SW1)
+#define BUTTON2	(D, SW2)
+
+#endif // BITMANIP_H
\ No newline at end of file
diff --git a/module02/ex02/interrupt.h b/module02/ex02/interrupt.h
new file mode 100644
index 0000000..dccc1c5
--- /dev/null
+++ b/module02/ex02/interrupt.h
@@ -0,0 +1,8 @@
+#ifndef INTERRUPT_H
+#define INTERRUPT_H
+
+// 7.3.1 : SREG – AVR Status Register
+#define ENABLE_GLOBAL_INTERRUPT		(1<<7)
+#define DISABLE_GLOBAL_INTERRUPT	(0<<7)
+
+#endif // INTERRUPT_H
\ No newline at end of file
diff --git a/module02/ex02/main.c b/module02/ex02/main.c
index 2a02658..ffbd7a3 100644
--- a/module02/ex02/main.c
+++ b/module02/ex02/main.c
@@ -2,120 +2,18 @@
 #include <util/delay.h>
 #include <avr/interrupt.h>
 
-// mathematics 
-#define DIV_ROUND_CLOSEST(n, d)	((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d))) // https://stackoverflow.com/a/18067292
-
-// stringify
-#define STRINGIFY_HELPER(x)		#x
-#define STRINGIFY(x)			STRINGIFY_HELPER(x)
-
-// concatenate
-#define CONCAT_HELPER(x, y)		x ## y
-#define CONCAT(x, y)			CONCAT_HELPER(x, y)
-
-// get argument
-#define ARG_1(v1, v2)			v1
-#define ARG_2(v1, v2)			v2
-#define GET_PORT(args)			ARG_1 args
-#define GET_BIT(args)			ARG_2 args
-// // version with "LED1 B, D1" without parenthesis
-// #define ARG_1(v1, ...)			v1
-// #define ARG_2(v1, v2, ...)		v2
-// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
-// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
-
-// actions on registers
-#define SET(register, bit)		register |= 1 << bit
-#define CLEAR(register, bit)	register &= ~(1 << bit)
-#define TEST(register, bit)		(register & 1 << bit)
-#define TOGGLE(register, bit)	register ^= 1 << bit
-
-// actions on elements
-#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
-#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
-#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
-#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
-#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
-#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
-#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)
-
-// bits
-#define D1	0
-#define D2	1
-#define D3	2
-#define D4	4
-#define SW1	2
-#define SW2	4
-
-// elements (port, bit)
-// #define LED1	B, D1
-#define LED1	(B, D1)
-#define LED2	(B, D2)
-#define LED3	(B, D3)
-#define LED4	(B, D4)
-#define BUTTON1	(D, SW1)
-#define BUTTON2	(D, SW2)
+#include "utils.h"
+#include "bitmanip.h"
+#include "usart.h"
 
 // USART
-// Table 20-1 : Baud Rate Calculation
-#define USART_BAUDRATE			115200
-#define BAUD_PRESCALER			(DIV_ROUND_CLOSEST(F_CPU, (16 * USART_BAUDRATE)) - 1)
-// Table 20-8 : Mode Selection (USART Mode SELect)
-#define ASYNCHRONOUS			(0<<UMSEL01 | 0<<UMSEL00)
-#define SYNCHRONOUS				(0<<UMSEL01 | 1<<UMSEL00)
-// Table 20-9 : Parity Bit Selection (USART Parity Mode)
-#define PARITY_DISABLED			(0<<UPM01 | 0<<UPM00)
-#define PARITY_EVEN				(1<<UPM01 | 0<<UPM00)
-#define PARITY_ODD				(1<<UPM01 | 1<<UPM00)
-// Table 20-10 : Stop Bit Selection (USART Stop Bit Select)
-#define STOP_ONE_BIT			(0<<USBS0)
-#define STOP_TWO_BIT			(1<<USBS0)
-// Table 20-11 : Data Bit Selection (USART Character SiZe)
-#define DATA_FIVE_BIT			(0<<UCSZ02 | 0<<UCSZ01 | 0<<UCSZ00)
-#define DATA_SIX_BIT			(0<<UCSZ02 | 0<<UCSZ01 | 1<<UCSZ00)
-#define DATA_SEVEN_BIT			(0<<UCSZ02 | 1<<UCSZ01 | 0<<UCSZ00)
-#define DATA_EIGHT_BIT			(0<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
-#define DATA_NINE_BIT			(1<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
-// 20.11.3 : USART Control and Status Register B (UCSRnB)
-#define RECEIVER_DISABLED		(0<<RXEN0)
-#define RECEIVER_ENABLED		(1<<RXEN0)
-#define TRANSMITTER_DISABLED	(0<<TXEN0)
-#define TRANSMITTER_ENABLED		(1<<TXEN0)
-
-// TIMER
-#define PERIOD							2000
-#define TIME_MS(ms)						(((F_CPU / PRESCALE_VALUE) * ms) / 1000)
-#define PRESCALE_VALUE					1024		// can be 1, 8, 64, 256, 1024
-// table 16-5 : prescale sets
-#define PRESCALE_SET(value)  \
-										((value) == 1   ? (0<<CS12 | 0<<CS11 | 1<<CS10) : \
-										 (value) == 8   ? (0<<CS12 | 1<<CS11 | 0<<CS10) : \
-										 (value) == 64  ? (0<<CS12 | 1<<CS11 | 1<<CS10) : \
-										 (value) == 256 ? (1<<CS12 | 0<<CS11 | 0<<CS10) : \
-										 (value) == 1024? (1<<CS12 | 0<<CS11 | 1<<CS10) : \
-														  (0<<CS12 | 0<<CS11 | 0<<CS10))
-// Table 16-4 : Waveform Generation Mode Bit Description
-#define CTC_TOP_OCR1A_IN_TCCR1B			(0<<WGM13 | 1<<WGM12)
-#define CTC_TOP_OCR1A_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
-#define CTC_TOP_ICR1_IN_TCCR1B			(1<<WGM13 | 1<<WGM12)
-#define CTC_TOP_ICR1_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
-#define FAST_PWM_TOP_OCR1A_IN_TCCR1B	(1<<WGM13 | 1<<WGM12)
-#define FAST_PWM_TOP_OCR1A_IN_TCCR1A							(1<<WGM11 | 1<<WGM10)
-#define FAST_PWM_TOP_ICR1_IN_TCCR1B		(1<<WGM13 | 1<<WGM12)
-#define FAST_PWM_TOP_ICR1_IN_TCCR1A								(1<<WGM11 | 0<<WGM10)
-// 16.11.8 : Timer/Counter1 Interrupt Mask Register
-#define INTERRUPT_ENABLE_CHANNEL_A		(1 << OCIE1A)
-#define INTERRUPT_DISABLE_CHANNEL_A		(0 << OCIE1A)
+#define USART_BAUDRATE		115200
 
 // END MACROS
 
 void uart_init() {
-	UBRR0H = (unsigned char) (BAUD_PRESCALER >> 8);								// 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
-	UBRR0L = (unsigned char) BAUD_PRESCALER;
+	UBRR0H = (unsigned char) (BAUD_PRESCALER(USART_BAUDRATE) >> 8);				// 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
+	UBRR0L = (unsigned char) BAUD_PRESCALER(USART_BAUDRATE);
 
 	UCSR0C |= ASYNCHRONOUS | PARITY_DISABLED | STOP_ONE_BIT | DATA_EIGHT_BIT;	// 20.11.4 : set Frame Format
 	
diff --git a/module02/ex02/timer.h b/module02/ex02/timer.h
new file mode 100644
index 0000000..2493232
--- /dev/null
+++ b/module02/ex02/timer.h
@@ -0,0 +1,27 @@
+#ifndef TIMER_H
+#define TIMER_H
+
+// table 16-5 : prescale sets
+#define PRESCALE_SET(value)  \
+									((value) == 1   ? (0<<CS12 | 0<<CS11 | 1<<CS10) : \
+									 (value) == 8   ? (0<<CS12 | 1<<CS11 | 0<<CS10) : \
+									 (value) == 64  ? (0<<CS12 | 1<<CS11 | 1<<CS10) : \
+									 (value) == 256 ? (1<<CS12 | 0<<CS11 | 0<<CS10) : \
+									 (value) == 1024? (1<<CS12 | 0<<CS11 | 1<<CS10) : \
+													  (0<<CS12 | 0<<CS11 | 0<<CS10))
+#define TIME_MS(ms, prescale_value)	(((F_CPU / prescale_value) * ms) / 1000)
+
+// Table 16-4 : Waveform Generation Mode Bit Description
+#define CTC_TOP_OCR1A_IN_TCCR1B			(0<<WGM13 | 1<<WGM12)
+#define CTC_TOP_OCR1A_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
+#define CTC_TOP_ICR1_IN_TCCR1B			(1<<WGM13 | 1<<WGM12)
+#define CTC_TOP_ICR1_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
+#define FAST_PWM_TOP_OCR1A_IN_TCCR1B	(1<<WGM13 | 1<<WGM12)
+#define FAST_PWM_TOP_OCR1A_IN_TCCR1A							(1<<WGM11 | 1<<WGM10)
+#define FAST_PWM_TOP_ICR1_IN_TCCR1B		(1<<WGM13 | 1<<WGM12)
+#define FAST_PWM_TOP_ICR1_IN_TCCR1A								(1<<WGM11 | 0<<WGM10)
+// 16.11.8 : Timer/Counter1 Interrupt Mask Register
+#define INTERRUPT_ENABLE_CHANNEL_A		(1 << OCIE1A)
+#define INTERRUPT_DISABLE_CHANNEL_A		(0 << OCIE1A)
+
+#endif // TIMER_H
\ No newline at end of file
diff --git a/module02/ex02/usart.h b/module02/ex02/usart.h
new file mode 100644
index 0000000..88d7fd0
--- /dev/null
+++ b/module02/ex02/usart.h
@@ -0,0 +1,27 @@
+#ifndef USART_H
+#define USART_H
+
+#define BAUD_PRESCALER(usart_baudrate)	(DIV_ROUND_CLOSEST(F_CPU, (16 * usart_baudrate)) - 1)
+// Table 20-8 : Mode Selection (USART Mode SELect)
+#define ASYNCHRONOUS					(0<<UMSEL01 | 0<<UMSEL00)
+#define SYNCHRONOUS						(0<<UMSEL01 | 1<<UMSEL00)
+// Table 20-9 : Parity Bit Selection (USART Parity Mode)
+#define PARITY_DISABLED					(0<<UPM01 | 0<<UPM00)
+#define PARITY_EVEN						(1<<UPM01 | 0<<UPM00)
+#define PARITY_ODD						(1<<UPM01 | 1<<UPM00)
+// Table 20-10 : Stop Bit Selection (USART Stop Bit Select)
+#define STOP_ONE_BIT					(0<<USBS0)
+#define STOP_TWO_BIT					(1<<USBS0)
+// Table 20-11 : Data Bit Selection (USART Character SiZe)
+#define DATA_FIVE_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 0<<UCSZ00)
+#define DATA_SIX_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 1<<UCSZ00)
+#define DATA_SEVEN_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 0<<UCSZ00)
+#define DATA_EIGHT_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
+#define DATA_NINE_BIT					(1<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
+// 20.11.3 : USART Control and Status Register B (UCSRnB)
+#define RECEIVER_DISABLED				(0<<RXEN0)
+#define RECEIVER_ENABLED				(1<<RXEN0)
+#define TRANSMITTER_DISABLED			(0<<TXEN0)
+#define TRANSMITTER_ENABLED				(1<<TXEN0)
+
+#endif // USART_H
\ No newline at end of file
diff --git a/module02/ex02/utils.h b/module02/ex02/utils.h
new file mode 100644
index 0000000..5c22e0b
--- /dev/null
+++ b/module02/ex02/utils.h
@@ -0,0 +1,16 @@
+#ifndef UTILS_H
+#define UTILS_H
+
+// stringify
+#define STRINGIFY_HELPER(x)			#x
+#define STRINGIFY(x)				STRINGIFY_HELPER(x)
+
+// concatenate
+#define CONCAT_HELPER(x, y)			x ## y
+#define CONCAT(x, y)				CONCAT_HELPER(x, y)
+
+// mathematics
+#define PERCENT(percent, total)		(((float)percent / 100) * total)
+#define DIV_ROUND_CLOSEST(n, d)		((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d)))
+
+#endif // UTILS_H
\ No newline at end of file
diff --git a/module02/ex03/bitmanip.h b/module02/ex03/bitmanip.h
new file mode 100644
index 0000000..4df44d1
--- /dev/null
+++ b/module02/ex03/bitmanip.h
@@ -0,0 +1,53 @@
+#ifndef BITMANIP_H
+#define BITMANIP_H
+
+#include "utils.h"
+
+// Bit operations on registers
+#define SET(register, bit)		(register |= (1 << (bit)))
+#define CLEAR(register, bit)	(register &= ~(1 << (bit)))
+#define TEST(register, bit)		(register & (1 << (bit)))
+#define TOGGLE(register, bit)	(register ^= (1 << (bit)))
+
+// Get arguments from tuple-like definitions
+#define ARG_1(v1, v2)			v1
+#define ARG_2(v1, v2)			v2
+#define GET_PORT(args)			ARG_1 args
+#define GET_BIT(args)			ARG_2 args
+// // version with "LED1 B, D1" without parenthesis
+// #define ARG_1(v1, ...)			v1
+// #define ARG_2(v1, v2, ...)		v2
+// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
+// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
+
+// Actions on elements
+// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
+#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+
+#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
+#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
+#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
+#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
+#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
+#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)
+
+// Bit definitions
+#define D1 0
+#define D2 1
+#define D3 2
+#define D4 4
+#define SW1 2
+#define SW2 4
+
+// Elements (port, bit)
+#define LED1	(B, D1)
+#define LED2	(B, D2)
+#define LED3	(B, D3)
+#define LED4	(B, D4)
+#define BUTTON1	(D, SW1)
+#define BUTTON2	(D, SW2)
+
+#endif // BITMANIP_H
\ No newline at end of file
diff --git a/module02/ex03/interrupt.h b/module02/ex03/interrupt.h
new file mode 100644
index 0000000..dccc1c5
--- /dev/null
+++ b/module02/ex03/interrupt.h
@@ -0,0 +1,8 @@
+#ifndef INTERRUPT_H
+#define INTERRUPT_H
+
+// 7.3.1 : SREG – AVR Status Register
+#define ENABLE_GLOBAL_INTERRUPT		(1<<7)
+#define DISABLE_GLOBAL_INTERRUPT	(0<<7)
+
+#endif // INTERRUPT_H
\ No newline at end of file
diff --git a/module02/ex03/main.c b/module02/ex03/main.c
index 9252415..64d9b0c 100644
--- a/module02/ex03/main.c
+++ b/module02/ex03/main.c
@@ -2,127 +2,24 @@
 #include <util/delay.h>
 #include <avr/interrupt.h>		// https://www.nongnu.org/avr-libc/user-manual/group__avr__interrupts.html
 
-// mathematics 
-#define DIV_ROUND_CLOSEST(n, d)	((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d))) // https://stackoverflow.com/a/18067292
-
-// stringify
-#define STRINGIFY_HELPER(x)		#x
-#define STRINGIFY(x)			STRINGIFY_HELPER(x)
-
-// concatenate
-#define CONCAT_HELPER(x, y)		x ## y
-#define CONCAT(x, y)			CONCAT_HELPER(x, y)
-
-// get argument
-#define ARG_1(v1, v2)			v1
-#define ARG_2(v1, v2)			v2
-#define GET_PORT(args)			ARG_1 args
-#define GET_BIT(args)			ARG_2 args
-// // version with "LED1 B, D1" without parenthesis
-// #define ARG_1(v1, ...)			v1
-// #define ARG_2(v1, v2, ...)		v2
-// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
-// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
-
-// actions on registers
-#define SET(register, bit)		register |= 1 << bit
-#define CLEAR(register, bit)	register &= ~(1 << bit)
-#define TEST(register, bit)		(register & 1 << bit)
-#define TOGGLE(register, bit)	register ^= 1 << bit
-
-// actions on elements
-#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
-#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
-#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
-#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
-#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
-#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
-#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)
-
-// bits
-#define D1	0
-#define D2	1
-#define D3	2
-#define D4	4
-#define SW1	2
-#define SW2	4
-
-// elements (port, bit)
-// #define LED1	B, D1
-#define LED1	(B, D1)
-#define LED2	(B, D2)
-#define LED3	(B, D3)
-#define LED4	(B, D4)
-#define BUTTON1	(D, SW1)
-#define BUTTON2	(D, SW2)
+#include "utils.h"
+#include "bitmanip.h"
+#include "timer.h"
+#include "usart.h"
+#include "interrupt.h"
 
 // USART
-// Table 20-1 : Baud Rate Calculation
 #define USART_BAUDRATE					115200
-#define BAUD_PRESCALER					(DIV_ROUND_CLOSEST(F_CPU, (16 * USART_BAUDRATE)) - 1)
-// Table 20-8 : Mode Selection (USART Mode SELect)
-#define ASYNCHRONOUS					(0<<UMSEL01 | 0<<UMSEL00)
-#define SYNCHRONOUS						(0<<UMSEL01 | 1<<UMSEL00)
-// Table 20-9 : Parity Bit Selection (USART Parity Mode)
-#define PARITY_DISABLED					(0<<UPM01 | 0<<UPM00)
-#define PARITY_EVEN						(1<<UPM01 | 0<<UPM00)
-#define PARITY_ODD						(1<<UPM01 | 1<<UPM00)
-// Table 20-10 : Stop Bit Selection (USART Stop Bit Select)
-#define STOP_ONE_BIT					(0<<USBS0)
-#define STOP_TWO_BIT					(1<<USBS0)
-// Table 20-11 : Data Bit Selection (USART Character SiZe)
-#define DATA_FIVE_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 0<<UCSZ00)
-#define DATA_SIX_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 1<<UCSZ00)
-#define DATA_SEVEN_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 0<<UCSZ00)
-#define DATA_EIGHT_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
-#define DATA_NINE_BIT					(1<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
-// 20.11.3 : USART Control and Status Register B (UCSRnB)
-#define RECEIVER_DISABLED				(0<<RXEN0)
-#define RECEIVER_ENABLED				(1<<RXEN0)
-#define TRANSMITTER_DISABLED			(0<<TXEN0)
-#define TRANSMITTER_ENABLED				(1<<TXEN0)
-#define INTERRUPT_RECEIVER_DISABLED		(0<<RXCIE0)
-#define INTERRUPT_RECEIVER_ENABLED		(1<<RXCIE0)
-#define INTERRUPT_TRANSMITTER_DISABLED	(0<<TXCIE0)
-#define INTERRUPT_TRANSMITTER_ENABLED	(1<<TXCIE0)
 
 // TIMER
 #define PERIOD							2000
-#define TIME_MS(ms)						(((F_CPU / PRESCALE_VALUE) * ms) / 1000)
 #define PRESCALE_VALUE					1024		// can be 1, 8, 64, 256, 1024
-// table 16-5 : prescale sets
-#define PRESCALE_SET(value)  \
-										((value) == 1   ? (0<<CS12 | 0<<CS11 | 1<<CS10) : \
-										 (value) == 8   ? (0<<CS12 | 1<<CS11 | 0<<CS10) : \
-										 (value) == 64  ? (0<<CS12 | 1<<CS11 | 1<<CS10) : \
-										 (value) == 256 ? (1<<CS12 | 0<<CS11 | 0<<CS10) : \
-										 (value) == 1024? (1<<CS12 | 0<<CS11 | 1<<CS10) : \
-														  (0<<CS12 | 0<<CS11 | 0<<CS10))
-// Table 16-4 : Waveform Generation Mode Bit Description
-#define CTC_TOP_OCR1A_IN_TCCR1B			(0<<WGM13 | 1<<WGM12)
-#define CTC_TOP_OCR1A_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
-#define CTC_TOP_ICR1_IN_TCCR1B			(1<<WGM13 | 1<<WGM12)
-#define CTC_TOP_ICR1_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
-#define FAST_PWM_TOP_OCR1A_IN_TCCR1B	(1<<WGM13 | 1<<WGM12)
-#define FAST_PWM_TOP_OCR1A_IN_TCCR1A							(1<<WGM11 | 1<<WGM10)
-#define FAST_PWM_TOP_ICR1_IN_TCCR1B		(1<<WGM13 | 1<<WGM12)
-#define FAST_PWM_TOP_ICR1_IN_TCCR1A								(1<<WGM11 | 0<<WGM10)
-// 16.11.8 : Timer/Counter1 Interrupt Mask Register
-#define INTERRUPT_ENABLE_CHANNEL_A		(1 << OCIE1A)
-#define INTERRUPT_DISABLE_CHANNEL_A		(0 << OCIE1A)
-
-// text
-#define SWITCH_CASE(ch) (((ch) >= 'A' && (ch) <= 'Z') || ((ch) >= 'a' && (ch) <= 'z') ? ((ch) ^ (1 << 5)) : (ch))
 
 // END MACROS
 
 void uart_init() {
-	UBRR0H = (unsigned char) (BAUD_PRESCALER >> 8);									// 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
-	UBRR0L = (unsigned char) BAUD_PRESCALER;
+	UBRR0H = (unsigned char) (BAUD_PRESCALER(USART_BAUDRATE) >> 8);									// 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
+	UBRR0L = (unsigned char) BAUD_PRESCALER(USART_BAUDRATE);
 
 	UCSR0C |= ASYNCHRONOUS | PARITY_DISABLED | STOP_ONE_BIT | DATA_EIGHT_BIT;		// 20.11.4 : set Frame Format
 	
@@ -141,8 +38,8 @@ void uart_tx(char c) {
 
 ISR(USART_RX_vect) {																// Table 12-7 : we select the code for USART Receive
 	// char received_char = uart_rx();
-	char received_char = UDR0;				// Read received character
-	uart_tx(SWITCH_CASE(received_char));	// Toggle case and send back
+	char received_char = UDR0;														// Read received character
+	uart_tx(SWITCH_CASE(received_char));											// Toggle case and send back
 }
 
 // send back caracters received on serial port with case toggling, using interupt and empty infinite loop
@@ -150,7 +47,7 @@ ISR(USART_RX_vect) {																// Table 12-7 : we select the code for USART
 int main() {
 	uart_init();
 
-	sei();																			// enable global interrupts
+	SREG |= ENABLE_GLOBAL_INTERRUPT;												// 7.3.1 : Status Register, bit 7 : I – Global Interrupt Enable
 
 	while(1);
 }
diff --git a/module02/ex03/timer.h b/module02/ex03/timer.h
new file mode 100644
index 0000000..2493232
--- /dev/null
+++ b/module02/ex03/timer.h
@@ -0,0 +1,27 @@
+#ifndef TIMER_H
+#define TIMER_H
+
+// table 16-5 : prescale sets
+#define PRESCALE_SET(value)  \
+									((value) == 1   ? (0<<CS12 | 0<<CS11 | 1<<CS10) : \
+									 (value) == 8   ? (0<<CS12 | 1<<CS11 | 0<<CS10) : \
+									 (value) == 64  ? (0<<CS12 | 1<<CS11 | 1<<CS10) : \
+									 (value) == 256 ? (1<<CS12 | 0<<CS11 | 0<<CS10) : \
+									 (value) == 1024? (1<<CS12 | 0<<CS11 | 1<<CS10) : \
+													  (0<<CS12 | 0<<CS11 | 0<<CS10))
+#define TIME_MS(ms, prescale_value)	(((F_CPU / prescale_value) * ms) / 1000)
+
+// Table 16-4 : Waveform Generation Mode Bit Description
+#define CTC_TOP_OCR1A_IN_TCCR1B			(0<<WGM13 | 1<<WGM12)
+#define CTC_TOP_OCR1A_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
+#define CTC_TOP_ICR1_IN_TCCR1B			(1<<WGM13 | 1<<WGM12)
+#define CTC_TOP_ICR1_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
+#define FAST_PWM_TOP_OCR1A_IN_TCCR1B	(1<<WGM13 | 1<<WGM12)
+#define FAST_PWM_TOP_OCR1A_IN_TCCR1A							(1<<WGM11 | 1<<WGM10)
+#define FAST_PWM_TOP_ICR1_IN_TCCR1B		(1<<WGM13 | 1<<WGM12)
+#define FAST_PWM_TOP_ICR1_IN_TCCR1A								(1<<WGM11 | 0<<WGM10)
+// 16.11.8 : Timer/Counter1 Interrupt Mask Register
+#define INTERRUPT_ENABLE_CHANNEL_A		(1 << OCIE1A)
+#define INTERRUPT_DISABLE_CHANNEL_A		(0 << OCIE1A)
+
+#endif // TIMER_H
\ No newline at end of file
diff --git a/module02/ex03/usart.h b/module02/ex03/usart.h
new file mode 100644
index 0000000..b930036
--- /dev/null
+++ b/module02/ex03/usart.h
@@ -0,0 +1,31 @@
+#ifndef USART_H
+#define USART_H
+
+#define BAUD_PRESCALER(usart_baudrate)	(DIV_ROUND_CLOSEST(F_CPU, (16 * usart_baudrate)) - 1)
+// Table 20-8 : Mode Selection (USART Mode SELect)
+#define ASYNCHRONOUS					(0<<UMSEL01 | 0<<UMSEL00)
+#define SYNCHRONOUS						(0<<UMSEL01 | 1<<UMSEL00)
+// Table 20-9 : Parity Bit Selection (USART Parity Mode)
+#define PARITY_DISABLED					(0<<UPM01 | 0<<UPM00)
+#define PARITY_EVEN						(1<<UPM01 | 0<<UPM00)
+#define PARITY_ODD						(1<<UPM01 | 1<<UPM00)
+// Table 20-10 : Stop Bit Selection (USART Stop Bit Select)
+#define STOP_ONE_BIT					(0<<USBS0)
+#define STOP_TWO_BIT					(1<<USBS0)
+// Table 20-11 : Data Bit Selection (USART Character SiZe)
+#define DATA_FIVE_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 0<<UCSZ00)
+#define DATA_SIX_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 1<<UCSZ00)
+#define DATA_SEVEN_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 0<<UCSZ00)
+#define DATA_EIGHT_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
+#define DATA_NINE_BIT					(1<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
+// 20.11.3 : USART Control and Status Register B (UCSRnB)
+#define RECEIVER_DISABLED				(0<<RXEN0)
+#define RECEIVER_ENABLED				(1<<RXEN0)
+#define TRANSMITTER_DISABLED			(0<<TXEN0)
+#define TRANSMITTER_ENABLED				(1<<TXEN0)
+#define INTERRUPT_RECEIVER_DISABLED		(0<<RXCIE0)
+#define INTERRUPT_RECEIVER_ENABLED		(1<<RXCIE0)
+#define INTERRUPT_TRANSMITTER_DISABLED	(0<<TXCIE0)
+#define INTERRUPT_TRANSMITTER_ENABLED	(1<<TXCIE0)
+
+#endif // USART_H
\ No newline at end of file
diff --git a/module02/ex03/utils.h b/module02/ex03/utils.h
new file mode 100644
index 0000000..800e807
--- /dev/null
+++ b/module02/ex03/utils.h
@@ -0,0 +1,19 @@
+#ifndef UTILS_H
+#define UTILS_H
+
+// stringify
+#define STRINGIFY_HELPER(x)			#x
+#define STRINGIFY(x)				STRINGIFY_HELPER(x)
+
+// concatenate
+#define CONCAT_HELPER(x, y)			x ## y
+#define CONCAT(x, y)				CONCAT_HELPER(x, y)
+
+// mathematics
+#define PERCENT(percent, total)		(((float)percent / 100) * total)
+#define DIV_ROUND_CLOSEST(n, d)		((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d)))
+
+// text
+#define SWITCH_CASE(ch) (((ch) >= 'A' && (ch) <= 'Z') || ((ch) >= 'a' && (ch) <= 'z') ? ((ch) ^ (1 << 5)) : (ch))
+
+#endif // UTILS_H
\ No newline at end of file
diff --git a/module02/ex04/bitmanip.h b/module02/ex04/bitmanip.h
new file mode 100644
index 0000000..4df44d1
--- /dev/null
+++ b/module02/ex04/bitmanip.h
@@ -0,0 +1,53 @@
+#ifndef BITMANIP_H
+#define BITMANIP_H
+
+#include "utils.h"
+
+// Bit operations on registers
+#define SET(register, bit)		(register |= (1 << (bit)))
+#define CLEAR(register, bit)	(register &= ~(1 << (bit)))
+#define TEST(register, bit)		(register & (1 << (bit)))
+#define TOGGLE(register, bit)	(register ^= (1 << (bit)))
+
+// Get arguments from tuple-like definitions
+#define ARG_1(v1, v2)			v1
+#define ARG_2(v1, v2)			v2
+#define GET_PORT(args)			ARG_1 args
+#define GET_BIT(args)			ARG_2 args
+// // version with "LED1 B, D1" without parenthesis
+// #define ARG_1(v1, ...)			v1
+// #define ARG_2(v1, v2, ...)		v2
+// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
+// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
+
+// Actions on elements
+// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
+#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+
+#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
+#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
+#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
+#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
+#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
+#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)
+
+// Bit definitions
+#define D1 0
+#define D2 1
+#define D3 2
+#define D4 4
+#define SW1 2
+#define SW2 4
+
+// Elements (port, bit)
+#define LED1	(B, D1)
+#define LED2	(B, D2)
+#define LED3	(B, D3)
+#define LED4	(B, D4)
+#define BUTTON1	(D, SW1)
+#define BUTTON2	(D, SW2)
+
+#endif // BITMANIP_H
\ No newline at end of file
diff --git a/module02/ex04/interrupt.h b/module02/ex04/interrupt.h
new file mode 100644
index 0000000..dccc1c5
--- /dev/null
+++ b/module02/ex04/interrupt.h
@@ -0,0 +1,8 @@
+#ifndef INTERRUPT_H
+#define INTERRUPT_H
+
+// 7.3.1 : SREG – AVR Status Register
+#define ENABLE_GLOBAL_INTERRUPT		(1<<7)
+#define DISABLE_GLOBAL_INTERRUPT	(0<<7)
+
+#endif // INTERRUPT_H
\ No newline at end of file
diff --git a/module02/ex04/main.c b/module02/ex04/main.c
index 0207079..41b68c1 100644
--- a/module02/ex04/main.c
+++ b/module02/ex04/main.c
@@ -2,127 +2,23 @@
 #include <util/delay.h>
 #include <avr/interrupt.h>		// https://www.nongnu.org/avr-libc/user-manual/group__avr__interrupts.html
 
-// mathematics 
-#define DIV_ROUND_CLOSEST(n, d)	((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d))) // https://stackoverflow.com/a/18067292
-
-// text
-#define SWITCH_CASE(ch)			(((ch) >= 'A' && (ch) <= 'Z') || ((ch) >= 'a' && (ch) <= 'z') ? ((ch) ^ (1 << 5)) : (ch))
-
-// stringify
-#define STRINGIFY_HELPER(x)		#x
-#define STRINGIFY(x)			STRINGIFY_HELPER(x)
-
-// concatenate
-#define CONCAT_HELPER(x, y)		x ## y
-#define CONCAT(x, y)			CONCAT_HELPER(x, y)
-
-// get argument
-#define ARG_1(v1, v2)			v1
-#define ARG_2(v1, v2)			v2
-#define GET_PORT(args)			ARG_1 args
-#define GET_BIT(args)			ARG_2 args
-// // version with "LED1 B, D1" without parenthesis
-// #define ARG_1(v1, ...)			v1
-// #define ARG_2(v1, v2, ...)		v2
-// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
-// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
-
-// actions on registers
-#define SET(register, bit)		register |= 1 << bit
-#define CLEAR(register, bit)	register &= ~(1 << bit)
-#define TEST(register, bit)		(register & 1 << bit)
-#define TOGGLE(register, bit)	register ^= 1 << bit
-
-// actions on elements
-#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
-#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
-#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
-#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
-#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
-#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
-#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
-#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)
-
-// bits
-#define D1	0
-#define D2	1
-#define D3	2
-#define D4	4
-#define SW1	2
-#define SW2	4
-
-// elements (port, bit)
-// #define LED1	B, D1
-#define LED1	(B, D1)
-#define LED2	(B, D2)
-#define LED3	(B, D3)
-#define LED4	(B, D4)
-#define BUTTON1	(D, SW1)
-#define BUTTON2	(D, SW2)
+#include "utils.h"
+#include "bitmanip.h"
+#include "timer.h"
+#include "usart.h"
+#include "interrupt.h"
 
 // USART
-// Table 20-1 : Baud Rate Calculation
-#define USART_BAUDRATE					115200
-#define BAUD_PRESCALER					(DIV_ROUND_CLOSEST(F_CPU, (16 * USART_BAUDRATE)) - 1)
-// Table 20-8 : Mode Selection (USART Mode SELect)
-#define ASYNCHRONOUS					(0<<UMSEL01 | 0<<UMSEL00)
-#define SYNCHRONOUS						(0<<UMSEL01 | 1<<UMSEL00)
-// Table 20-9 : Parity Bit Selection (USART Parity Mode)
-#define PARITY_DISABLED					(0<<UPM01 | 0<<UPM00)
-#define PARITY_EVEN						(1<<UPM01 | 0<<UPM00)
-#define PARITY_ODD						(1<<UPM01 | 1<<UPM00)
-// Table 20-10 : Stop Bit Selection (USART Stop Bit Select)
-#define STOP_ONE_BIT					(0<<USBS0)
-#define STOP_TWO_BIT					(1<<USBS0)
-// Table 20-11 : Data Bit Selection (USART Character SiZe)
-#define DATA_FIVE_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 0<<UCSZ00)
-#define DATA_SIX_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 1<<UCSZ00)
-#define DATA_SEVEN_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 0<<UCSZ00)
-#define DATA_EIGHT_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
-#define DATA_NINE_BIT					(1<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
-// 20.11.3 : USART Control and Status Register B (UCSRnB)
-#define RECEIVER_DISABLED				(0<<RXEN0)
-#define RECEIVER_ENABLED				(1<<RXEN0)
-#define TRANSMITTER_DISABLED			(0<<TXEN0)
-#define TRANSMITTER_ENABLED				(1<<TXEN0)
-#define INTERRUPT_RECEIVER_DISABLED		(0<<RXCIE0)
-#define INTERRUPT_RECEIVER_ENABLED		(1<<RXCIE0)
-#define INTERRUPT_TRANSMITTER_DISABLED	(0<<TXCIE0)
-#define INTERRUPT_TRANSMITTER_ENABLED	(1<<TXCIE0)
-
+#define USART_BAUDRATE		115200
 // TIMER
-#define PERIOD							2000
-#define TIME_MS(ms)						(((F_CPU / PRESCALE_VALUE) * ms) / 1000)
-#define PRESCALE_VALUE					1024		// can be 1, 8, 64, 256, 1024
-// table 16-5 : prescale sets
-#define PRESCALE_SET(value)  \
-										((value) == 1   ? (0<<CS12 | 0<<CS11 | 1<<CS10) : \
-										 (value) == 8   ? (0<<CS12 | 1<<CS11 | 0<<CS10) : \
-										 (value) == 64  ? (0<<CS12 | 1<<CS11 | 1<<CS10) : \
-										 (value) == 256 ? (1<<CS12 | 0<<CS11 | 0<<CS10) : \
-										 (value) == 1024? (1<<CS12 | 0<<CS11 | 1<<CS10) : \
-														  (0<<CS12 | 0<<CS11 | 0<<CS10))
-// Table 16-4 : Waveform Generation Mode Bit Description
-#define CTC_TOP_OCR1A_IN_TCCR1B			(0<<WGM13 | 1<<WGM12)
-#define CTC_TOP_OCR1A_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
-#define CTC_TOP_ICR1_IN_TCCR1B			(1<<WGM13 | 1<<WGM12)
-#define CTC_TOP_ICR1_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
-#define FAST_PWM_TOP_OCR1A_IN_TCCR1B	(1<<WGM13 | 1<<WGM12)
-#define FAST_PWM_TOP_OCR1A_IN_TCCR1A							(1<<WGM11 | 1<<WGM10)
-#define FAST_PWM_TOP_ICR1_IN_TCCR1B		(1<<WGM13 | 1<<WGM12)
-#define FAST_PWM_TOP_ICR1_IN_TCCR1A								(1<<WGM11 | 0<<WGM10)
-// 16.11.8 : Timer/Counter1 Interrupt Mask Register
-#define INTERRUPT_ENABLE_CHANNEL_A		(1 << OCIE1A)
-#define INTERRUPT_DISABLE_CHANNEL_A		(0 << OCIE1A)
+#define PERIOD				2000
+#define PRESCALE_VALUE		1024													// can be 1, 8, 64, 256, 1024
 
 // END MACROS
 
 void uart_init() {
-	UBRR0H = (unsigned char) (BAUD_PRESCALER >> 8);									// 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
-	UBRR0L = (unsigned char) BAUD_PRESCALER;
+	UBRR0H = (unsigned char) (BAUD_PRESCALER(USART_BAUDRATE) >> 8);									// 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
+	UBRR0L = (unsigned char) BAUD_PRESCALER(USART_BAUDRATE);
 
 	UCSR0C |= ASYNCHRONOUS | PARITY_DISABLED | STOP_ONE_BIT | DATA_EIGHT_BIT;		// 20.11.4 : set Frame Format
 	
@@ -151,12 +47,12 @@ ISR(USART_RX_vect) {																// Table 12-7 : we select the code for USART
 	}
 }
 
-// send back caracters received on serial port with case toggling, using interupt and empty infinite loop
+// ask for username and password
 // `screen /dev/ttyUSB0 115200`
 int main() {
 	uart_init();
 
-	sei();																			// enable global interrupts
+	SREG |= ENABLE_GLOBAL_INTERRUPT;												// 7.3.1 : Status Register, bit 7 : I – Global Interrupt Enable
 
 	while(1);
 }
diff --git a/module02/ex04/timer.h b/module02/ex04/timer.h
new file mode 100644
index 0000000..2493232
--- /dev/null
+++ b/module02/ex04/timer.h
@@ -0,0 +1,27 @@
+#ifndef TIMER_H
+#define TIMER_H
+
+// table 16-5 : prescale sets
+#define PRESCALE_SET(value)  \
+									((value) == 1   ? (0<<CS12 | 0<<CS11 | 1<<CS10) : \
+									 (value) == 8   ? (0<<CS12 | 1<<CS11 | 0<<CS10) : \
+									 (value) == 64  ? (0<<CS12 | 1<<CS11 | 1<<CS10) : \
+									 (value) == 256 ? (1<<CS12 | 0<<CS11 | 0<<CS10) : \
+									 (value) == 1024? (1<<CS12 | 0<<CS11 | 1<<CS10) : \
+													  (0<<CS12 | 0<<CS11 | 0<<CS10))
+#define TIME_MS(ms, prescale_value)	(((F_CPU / prescale_value) * ms) / 1000)
+
+// Table 16-4 : Waveform Generation Mode Bit Description
+#define CTC_TOP_OCR1A_IN_TCCR1B			(0<<WGM13 | 1<<WGM12)
+#define CTC_TOP_OCR1A_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
+#define CTC_TOP_ICR1_IN_TCCR1B			(1<<WGM13 | 1<<WGM12)
+#define CTC_TOP_ICR1_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
+#define FAST_PWM_TOP_OCR1A_IN_TCCR1B	(1<<WGM13 | 1<<WGM12)
+#define FAST_PWM_TOP_OCR1A_IN_TCCR1A							(1<<WGM11 | 1<<WGM10)
+#define FAST_PWM_TOP_ICR1_IN_TCCR1B		(1<<WGM13 | 1<<WGM12)
+#define FAST_PWM_TOP_ICR1_IN_TCCR1A								(1<<WGM11 | 0<<WGM10)
+// 16.11.8 : Timer/Counter1 Interrupt Mask Register
+#define INTERRUPT_ENABLE_CHANNEL_A		(1 << OCIE1A)
+#define INTERRUPT_DISABLE_CHANNEL_A		(0 << OCIE1A)
+
+#endif // TIMER_H
\ No newline at end of file
diff --git a/module02/ex04/usart.h b/module02/ex04/usart.h
new file mode 100644
index 0000000..b930036
--- /dev/null
+++ b/module02/ex04/usart.h
@@ -0,0 +1,31 @@
+#ifndef USART_H
+#define USART_H
+
+#define BAUD_PRESCALER(usart_baudrate)	(DIV_ROUND_CLOSEST(F_CPU, (16 * usart_baudrate)) - 1)
+// Table 20-8 : Mode Selection (USART Mode SELect)
+#define ASYNCHRONOUS					(0<<UMSEL01 | 0<<UMSEL00)
+#define SYNCHRONOUS						(0<<UMSEL01 | 1<<UMSEL00)
+// Table 20-9 : Parity Bit Selection (USART Parity Mode)
+#define PARITY_DISABLED					(0<<UPM01 | 0<<UPM00)
+#define PARITY_EVEN						(1<<UPM01 | 0<<UPM00)
+#define PARITY_ODD						(1<<UPM01 | 1<<UPM00)
+// Table 20-10 : Stop Bit Selection (USART Stop Bit Select)
+#define STOP_ONE_BIT					(0<<USBS0)
+#define STOP_TWO_BIT					(1<<USBS0)
+// Table 20-11 : Data Bit Selection (USART Character SiZe)
+#define DATA_FIVE_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 0<<UCSZ00)
+#define DATA_SIX_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 1<<UCSZ00)
+#define DATA_SEVEN_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 0<<UCSZ00)
+#define DATA_EIGHT_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
+#define DATA_NINE_BIT					(1<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
+// 20.11.3 : USART Control and Status Register B (UCSRnB)
+#define RECEIVER_DISABLED				(0<<RXEN0)
+#define RECEIVER_ENABLED				(1<<RXEN0)
+#define TRANSMITTER_DISABLED			(0<<TXEN0)
+#define TRANSMITTER_ENABLED				(1<<TXEN0)
+#define INTERRUPT_RECEIVER_DISABLED		(0<<RXCIE0)
+#define INTERRUPT_RECEIVER_ENABLED		(1<<RXCIE0)
+#define INTERRUPT_TRANSMITTER_DISABLED	(0<<TXCIE0)
+#define INTERRUPT_TRANSMITTER_ENABLED	(1<<TXCIE0)
+
+#endif // USART_H
\ No newline at end of file
diff --git a/module02/ex04/utils.h b/module02/ex04/utils.h
new file mode 100644
index 0000000..800e807
--- /dev/null
+++ b/module02/ex04/utils.h
@@ -0,0 +1,19 @@
+#ifndef UTILS_H
+#define UTILS_H
+
+// stringify
+#define STRINGIFY_HELPER(x)			#x
+#define STRINGIFY(x)				STRINGIFY_HELPER(x)
+
+// concatenate
+#define CONCAT_HELPER(x, y)			x ## y
+#define CONCAT(x, y)				CONCAT_HELPER(x, y)
+
+// mathematics
+#define PERCENT(percent, total)		(((float)percent / 100) * total)
+#define DIV_ROUND_CLOSEST(n, d)		((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d)))
+
+// text
+#define SWITCH_CASE(ch) (((ch) >= 'A' && (ch) <= 'Z') || ((ch) >= 'a' && (ch) <= 'z') ? ((ch) ^ (1 << 5)) : (ch))
+
+#endif // UTILS_H
\ No newline at end of file