USART problems with ATmega16

Question

I have a ATMega16 and have looped the Rx Tx (just connected the Rx to the Tx), to send and receive one char in a loop. But i only seems to be receiving 0x00 instead of the char i send. I have the CPU configured to 1MHz. But my thought is that since the Rx and Tx are just looped, it shouldn't matter what speed i set, since both are the same?

So basically, I'm trying to get a LED to flash at PORTC when receiving the correct char.

Here is the code:

#ifndef F_CPU
#define F_CPU 10000000
#endif

#define BAUD 9600
#define BAUDRATE ((F_CPU)/(BAUD*16)-1)
#include <avr/io.h>
#include <util/delay.h>



void uart_init(void){
    UBRRH = (BAUDRATE>>8);
    UBRRL = BAUDRATE;
    UCSRB = (1<<TXEN) | (1<<RXEN);
    UCSRC = (1<<URSEL) | (1<<UCSZ0) | (1<<UCSZ1);
}

void uart_transmit (unsigned char data){
    while (!(UCSRA & (1<<UDRE)));
    UDR = data;
}

unsigned char uart_recive(void){
    while(!(UCSRA) & (1<<RXC));
    return UDR;
}

int main(void)
{
    uart_init();
    unsigned char c;
    PORTC = 0xff;
    DDRC = 0xff;
    while(1)
    {
        _delay_ms(200);
        uart_transmit(0x2B);
        c = uart_recive();
        if(c==0x2B){
        PORTC = PORTC ^ 0xff;
        }
    }
}

Any thoughts of what i am doing wrong?

tzortzik tzortzik · Accepted Answer · 2014-03-08T09:31:58

The code seems right.

Thing you may have to check:

if your baudrate is the one you should have
if you try to send a char like 'p'; now you are sending a '+'
check your port configuration and see if it matches to your configuration

I think the last one is the problem.

You can try this code from ATMega manual:

/* Set frame format: 8data, 2stop bit */
UCSRC = (1<<URSEL)|(1<<USBS)|(3<<UCSZ0);

After building your program, go to your port configuration and make sure it it set on 8 bits data format and 2 stop bits. Then test it on you microcontroller and see what happens. Please come back with the result.

USART problems with ATmega16

4 Answers