CODEWITHSUNDEEP
cserial-portavravr-gcc
Jim
Jim

Reputation: 829

Help with AVR and Serial ports

I'm having problems with serial communication. I've connected an AtMega644 to a serial LCD which takes 9600 8N1. I just get garbage. By garbage I'm just getting some U,P,T and @ instead of the desired "U". I'm using the internal 8Mhz RC Osc with the fuses listed below. I suspect a timing issue but I'm not sure where I went wrong. I added a blinking LED and the timing looks right (eyeball and digital stopwatch). Any help is appreciated.

avrdude -pm644 -cavrisp2 -Pusb -b2400 -u -Uflash:w:ImpactTarget.hex:a -Ulfuse:w:0xe2:m -Uhfuse:w:0xd8:m -Uefuse:w:0xff:m

#define F_CPU 8000000
#define BAUDRATE 9600
#define UBRRVAL (F_CPU/(BAUDRATE*16UL)) -1


#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
#include <stdio.h>



/***************************************************** USART_Init()
*
*
**/
void USART_Init () {
    //Set baud rate
    UBRR0H = (unsigned char)(UBRRVAL>>8);   //high byte
    UBRR0L = (unsigned char) UBRRVAL;       //low byte

    //Asynchronous normal speed
    UCSR0A = (0<<U2X0);

    //Enable Transmitter and Receiver and Interrupt on receive complete
    UCSR0B = (1<<RXEN0) | (1<<TXEN0) | (1<<RXCIE0);

    //page 186 Set asynchronous mode,no parity, 1 stop bit, 8 bit size
    UCSR0C= (0<<UMSEL00)| (0<<UMSEL01)|             //Async
            (0<<UPM00)  | (0<<UPM01)  |             //Parity None
            (0<<USBS0)  |                           //Stop bits 1
            (0<<UCSZ02) | (1<<UCSZ01) |(1<<UCSZ00); //8 Bits

    //enable interrupts
    sei();
}


/******************************************** send_btye
* sends one byte to serial port
**/
void send_byte (char data) {
    while ( ! (UCSR0A & (1<<UDRE0)) )
        /* NOOP */;
    UDR0 = data;
}


/**
 * _delay_ms has a short time so this is an extension
 */
void delay_ms (int time) {
    for (int i = 0; i < time; i++) {
        _delay_ms(1);
    }
}

/****************************** main *********/
int main () {
    USART_Init();
    DDRA = 0xff;

    for (;;) {
        send_byte('U');
        delay_ms(500);
        PORTA ^=_BV(PA0);
    }

    return 0;
}

Upvotes: 0

Views: 1500

Answers (3)

Naeem Aleahmadi
Naeem Aleahmadi

Reputation: 1

this is exactly what took 3 days of my project time, just try to set Baudrate at (9600) and set the (X2) option for Baudrate. it should work.

Upvotes: -1

Ben Jackson
Ben Jackson

Reputation: 93700

Your UBRRVAL doesn't fully parenthesize its expression so when it is expanded in a context like UBRRVAL >> 8 the >> 8 does not apply the way you expect.

Upvotes: 2

Jens Willy Johannsen
Jens Willy Johannsen

Reputation: 764

I think you're right - it's probably a timing issue: the internal RC oscillator is usually much too imprecise to use for USART.

I would try to attach an external crystal (and set the fuses correspondingly) and see if it helps.

Upvotes: -1

Related Questions