diff --git a/adc.c b/adc.c
index c147a8d..1704ccc 100644
--- a/adc.c
+++ b/adc.c
@@ -5,13 +5,13 @@
 #include "adc.h"
 
 void adc_init(void) {
-    ADCSRA = 0b10000000; // Enable, the ADC, no interrupts, prescaler 2
+    ADCSRA = 0b10000111; // Enable, the ADC, no interrupts, Prescaler 128
     ADCSRB = 0x00; // Right adjusted, data
 }
 
 uint16_t adc_read_sync(uint8_t channel) {
-    ADMUX = 1 << REFS0 | channel; // Internal Ref | Select the channel
-    ADCSRA |= 1 << ADSC; // Start conversion
-    while(ADCSRA & (1 << ADSC)); // conversion running
-    return ADCL | ADCH << 8; // Low byte must be read first
+    ADMUX = 0b01u << 6 | channel; // Internal Ref | Select the channel
+    ADCSRA |= 1u << ADSC; // Start conversion
+    while(ADCSRA & (1u << ADSC)); // conversion running
+    return ADCL | (ADCH << 8u); // Low byte must be read first
 }
diff --git a/spi.c b/spi.c
index b493032..6657888 100644
--- a/spi.c
+++ b/spi.c
@@ -15,9 +15,10 @@ static volatile uint16_t _size = 0;
 static void (*_callback)(void) = 0;
 
 ISR(SPI_STC_vect) {
-    _buf[-1] = SPDR;
+    *_buf = SPDR;
+    ++_buf;
     if (_size > 0) {
-        SPDR = *_buf++;
+        SPDR = *_buf;
         --_size;
     } else {
         if (_callback != 0) {
@@ -26,13 +27,17 @@ ISR(SPI_STC_vect) {
     }
 }
 
-void spi_init(bool lsb_first, uint8_t f_bit) {
+void spi_init(bool lsb_first, spi_prescaler_t prescaler) {
     SPCR = 0b11010000; // Enabled, Interrupts enabled, Slave mode
     if (lsb_first) {
         SPCR |= (1 << DORD);
     }
-    SPCR |= f_bit & 0b11;
-    SPSR = (f_bit >> 2) & 0b1;
+    SPCR |= prescaler & 0b11u;
+    SPSR = (prescaler >> 2u) & 0b1u;
+
+#if defined(__AVR_ATmega328P__)
+    DDRB |= (1 << 3u) | (1 << 5u); // MOSI and SCK as Output
+#endif
 }
 
 void spi_tx_rx(uint8_t *buf, uint16_t size, void (*callback)(void)) {
@@ -40,7 +45,17 @@ void spi_tx_rx(uint8_t *buf, uint16_t size, void (*callback)(void)) {
     _size = size;
     _callback = callback;
     if (_size > 0) {
-        SPDR = *_buf++;
+        SPDR = *_buf;
         --_size;
     }
 }
+
+void spi_set_prescaler(spi_prescaler_t prescaler) {
+    uint8_t spcr = SPCR;
+    uint8_t spsr = SPSR;
+    spcr &= ~(0b11u); // Mask away the old prescaler bits
+    spsr &= ~(0b1u);
+
+    SPCR |= prescaler & 0b11u;
+    SPSR = (prescaler >> 2u) & 0b1u;
+}
diff --git a/spi.h b/spi.h
index f2964df..5dfbf7a 100644
--- a/spi.h
+++ b/spi.h
@@ -11,12 +11,25 @@
 #include <stdbool.h>
 #include <stdint.h>
 
+typedef enum {
+    DIV_2 = 0b100,
+    DIV_4 = 0b000,
+    DIV_8 = 0b101,
+    DIV_16 = 0b001,
+    DIV_32 = 0b110,
+    DIV_64 = 0b010,
+    DIV_64_2X = 0b111,
+    DIV_128 = 0b011
+} spi_prescaler_t;
+
 /**
  * Initialize and enable the spi in master mode.
  * @param lsb_first true if the data should be send (and received) with the least significant bit first
- * @param f_bit the 3 bits responsible for selecting the prescaler (refer to page 198 for more information)
+ * @param prescaler the 3 bits responsible for selecting the prescaler (refer to page 198 for more information)
  */
-void spi_init(bool lsb_first, uint8_t f_bit);
+void spi_init(bool lsb_first, spi_prescaler_t prescaler);
+
+void spi_set_prescaler(spi_prescaler_t prescaler);
 
 /**
  * Send and receive a number of bytes via the interface. The buffer is used for reading the data to send
diff --git a/timer8bit.c b/timer8bit.c
index adca032..642d4f0 100644
--- a/timer8bit.c
+++ b/timer8bit.c
@@ -10,19 +10,38 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 
-static void (*_callback)(void);
+typedef struct {
+    volatile timer_callback_t callback;
+    volatile uint8_t * const tccra, * const tccrb, * const timsk, * const tcnt;
+} timer8bit_instance_t;
 
+static volatile timer8bit_instance_t instance = {
+#if defined(__AVR_ATmega328P__)
+    .tccra = &TCCR2A, .tccrb = &TCCR2B, .timsk = &TIMSK2, .tcnt = &TCNT2
+#elif defined (__AVR_ATmega2560__)
+    .tccra = &TCCR0A, .tccrb = &TCCR0B, .timsk = &TIMSK0, .tcnt = &TCNT0
+#else
+    #error "Please define a CPU, using the mmcpu flag"
+#endif
+};
+
+
+
+#if defined(__AVR_ATmega328P__)
+ISR(TIMER2_OVF_vect) {
+#elif defined (__AVR_ATmega2560__)
 ISR(TIMER0_OVF_vect) {
-    if (_callback != 0) {
-        (*_callback)();
+#endif
+    if (instance.callback != 0) {
+        (*instance.callback)();
     }
 }
 
-void timer0_init(timer_clock_option_t timer_clock_option, void (*callback)(void)) {
-    _callback = callback;
-    TCCR0A = 0b00000000u; // Output compare disconnected, normal mode
-    TCCR0B = 0b00000000u | timer_clock_option; // No force override, normal mode, prescaler
-    TIMSK0 = 0b00000001u; // Overflow interrupt enabled
+void timer_8bit_init(timer_clock_option_t timer_clock_option, timer_callback_t callback) {
+    instance.callback = callback;
+    *instance.tccra = 0b00000000u; // Output compare disconnected, normal mode
+    *instance.tccrb = 0b00000000u | timer_clock_option; // No force override, normal mode, prescaler
+    *instance.timsk = 0b00000001u; // Overflow interrupt enabled
 
-    TCNT0 = 0; // Set the counter to 0
+    *instance.tcnt = 0; // Set the counter to 0
 }
diff --git a/timer8bit.h b/timer8bit.h
index 521ce2c..7e072c4 100644
--- a/timer8bit.h
+++ b/timer8bit.h
@@ -8,7 +8,21 @@
 #ifndef AVR_HAL_TIMER8BIT_H
 #define AVR_HAL_TIMER8BIT_H
 
+typedef void (*timer_callback_t)(void);
+
+#include <avr/io.h>
+
 typedef enum {
+#if defined(__AVR_ATmega328P__)
+    no_clock = 0,
+    prescaler_1 = 1,
+    prescaler_8 = 2,
+    prescaler_32 = 3,
+    prescaler_64 = 4,
+    prescaler_128 = 5,
+    prescaler_256 = 6,
+    prescaler_1024 = 7
+#elif defined (__AVR_ATmega2560__)
     no_clock = 0,
     prescaler_1 = 1,
     prescaler_8 = 2,
@@ -17,6 +31,7 @@ typedef enum {
     prescaler_1024 = 5,
     external_falling = 6,
     external_rising = 7
+#endif
 } timer_clock_option_t;
 
 /**
@@ -24,6 +39,6 @@ typedef enum {
  * @param timer_clock_option the prescaler
  * @param callback a functor that gets called on every overflow
  */
-void timer0_init(timer_clock_option_t timer_clock_option, void (*callback)(void));
+void timer_8bit_init(timer_clock_option_t timer_clock_option, void (*callback)(void));
 
 #endif //AVR_HAL_TIMER8BIT_H
diff --git a/uart.c b/uart.c
index 060bf04..988a5dd 100644
--- a/uart.c
+++ b/uart.c
@@ -13,6 +13,10 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 
+#ifndef UDR1
+    #define SINGLE_UART 1
+#endif
+
 #define RING_BUFFER_SIZE 64
 
 #define MIN_U2X_BAUD (F_CPU/(16*(255 + 1)) + 1)
@@ -69,17 +73,12 @@ void rx_handler(uint8_t id) {
     }
 }
 
-#ifndef UDR0 // Only one UART
+#if SINGLE_UART
 ISR(USART_RX_vect) { rx_handler(0); }
 ISR(USART_TX_vect) { tx_handler(0); }
-#endif
-
-#ifdef UDR0
+#else
 ISR(USART0_RX_vect) { rx_handler(0); }
 ISR(USART0_TX_vect) { tx_handler(0); }
-#endif
-
-#ifdef UDR1
 ISR(USART1_RX_vect) { rx_handler(1); }
 ISR(USART1_TX_vect) { tx_handler(1); }
 #endif
@@ -94,6 +93,9 @@ ISR(USART3_TX_vect) { tx_handler(3); }
 #endif
 
 void uart_init(uint8_t id, uint32_t baud, uart_parity_t parity, uint8_t stop_bits, uart_callback_t rx_callback) {
+#if SINGLE_UART
+    id = 0;
+#endif
     instances[id].callback = rx_callback;
     instances[id].tail = 0;
     instances[id].head = 0;
@@ -115,6 +117,9 @@ void uart_init(uint8_t id, uint32_t baud, uart_parity_t parity, uint8_t stop_bit
 }
 
 void uart_send_byte(uint8_t id, uint8_t data) {
+#if SINGLE_UART
+    id = 0;
+#endif
     if (instances[id].ready) { // Can send directly
         instances[id].ready = false;
         *instances[id].udr = data;