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Kod: Markera allt

    ATmega168               MAX233A               DB9 (hane)
    .--------.       .------------------.         .-------.
    |  2 RXD +-------+ 3 R1OUT   4 R1IN +---------+ 2 RXD |
    |  3 TXD +-------+ 2 T1IN   5 T1OUT +---------+ 3 TXD |
    .        .    .--+ 12 V-  7   11 C+ +--.    .-+ 5 GND |
    .        .    '--+ 17 V-  V   15 C+ +--'    | '-------'
    |        |    .--+ 9 GND  c  16 C2- +--.   ---
    '--------'    +--+ 6 GND  c  10 C2- +--'    -
                  |  '--------+---------'
                 ---          |
                  -          5V

Kod: Markera allt

#include <avr/io.h>

void USART_Init(unsigned int ubrr)
{
   /* Set baud rate */
   UBRR0H = (unsigned char)(ubrr>>8);
   UBRR0L = (unsigned char)ubrr;

   /* Enable the transmitter */
   UCSR0B = (1<<TXEN0);
}


void USART_Transmit(unsigned char data)
{
   /* Wait for empty transmit buffer */
   while( !(UCSR0A & (1<<UDRE0)));

   /* Put data into buffer, send the data */
   UDR0 = data;
}


int main(void) {

   USART_Init(25); /* 19k2 @ 8MHz */

   for(;;) {
      USART_Transmit('a');
      USART_Transmit('\r');
      USART_Transmit('\n');
   }
}