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USART Issues

Discussion in 'AVR' started by Billt321, Jul 19, 2015.

  1. Billt321

    Billt321 New Member

    Jul 19, 2015

    Recently i have been trying to get interrupt driven serial working for a project of mine, however i have been struggling to get it to work. I am using an Atmega328p (16Mhz external xtal), and an FTDI231x to communicate to a PC . I believe all the hardware works fine, as using Arduino IDE i can get the serial to work, but i need to use it in Atmel Studio 6. The transmit sort of works, i can see the Tx LED flashing, however i only see zeros or symbols with Realterm. The data sent by the AVR looks to be wrong on a scope aswell. Also, when sending data to the AVR, the Rx interrupt doesn't fire either. I have also tried a lot of example code of the web, checking to ensure that the Fcpu values and such were correct, and none have worked. I have also disabled ckdiv8 in the fuses. Any suggestions?

    Thanks in advance, Bill.

    Code (text):
    #include <avr/io.h>
    #include <util/delay.h>

    #define F_CPU 16000000UL
    #define FOSC 16000000
    #define BAUD 9600
    #define MYUBRR (FOSC/16/BAUD)-1

    volatile char usartReceive;
    volatile int rxF;
    unsigned char buffer;

    void USART_init();


    int main(){  
        while ( !( UCSR0A & (1<<UDRE0)) ) // Wait until buffer is empty
            buffer = "Hello";
            UDR0 = buffer;      
        //Main Loop
            while ( !( UCSR0A & (1<<UDRE0)) )
                UDR0 = 0b01010101
            if(rxF == 1){
                while ( !( UCSR0A & (1<<UDRE0)) )
                UDR0 = usartReceive;
                rxF = 0;

    void USART_init(){

        UBRR0H = (unsigned long)(MYUBRR>>8);
        UBRR0L = (unsigned long)(MYUBRR);
        UCSR0B |= (1<<RXEN0)|(1<<TXEN0)|(1<<RXCIE0);
        UCSR0C |= (1<<UCSZ01)|(1<<UCSZ00);    // 8 Data bits, one stop bit

    ISR (USART_RX_vect){
        usartReceive = UDR0;
        rxF = 1;

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