Problem with Atmega8 USART interrupt

[Sharagim]

Hi,
I am trying to run receive interrupt on atmega8 USART, and failed.
Without interrupt it is ok and working but seems the "USART_RXC_vect" never fire.
thanks in advance for any comment which help me to solve it.

#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
#define F_CPU 8000000
#define USART_BAUDRATE 19200
#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)


ISR(USART_RXC_vect)
{
   char ReceivedByte;
   ReceivedByte = UDR; // Fetch the received byte value into the variable "ByteReceived"
   UDR = ReceivedByte; // Echo back the received byte back to the computer
}

int main(void){
   UBRRL = BAUD_PRESCALE;
   UBRRH = (BAUD_PRESCALE >> 8);
   UCSRC |= (1 << URSEL) | (1 << UCSZ0) | (1 << UCSZ1);
   UCSRB |= (1 << RXEN) | (1 << TXEN);
   UCSRB |= (1 << RXCIE);
   sei();
    while(1)
    {

    }
}

 

[diegobb]

I don't remember exactly where it it's located in the datasheet, but when you write to 16 bit registers (Like UBRR) you must write the high byte first.

Try inverting the order in which you write in UBRR, this way:

UBRRH = (BAUD_PRESCALE >> 8);
UBRRL = BAUD_PRESCALE;

Look at the page 135 of the datsheet.

Best Regards.

 

[Sharagim]

Thanks for your reply .
I did as you mention but nothing happened, same as before!

 

[alexan_e]

Your code is working fine , it is the example posted in the last page of Interrupt Driven USART in AVR-GCC
https://www.fourwalledcubicle.com/AVRArticles.php

Alex

 

[Sharagim]

Finally I found the problem .
I am using AVRStudio5 and in that I have to use "ISR(USART__RXC_vect)" instead of "ISR(USART_RXC_vect)" .

BR,

 

[alexan_e]

I have only checked AVR studio 5 when it was a beta version, I keep using the version 4 but it doesn't make sense, why would they change the interrupt definition in the new version?
So in the m8 header how is USART_RXC_vect defined, it has to be defined or you would get an error?

 

[Sharagim]

No error.
I try to put some values like "ISR(USART_RXC_vect1111)" and compiled without error too !!!!

 

[vinodstanur]

It will not show error.. But will show warning...

like:
test_uart.c:48:1: warning: 'USART_RXC_vectttttttt' appears to be a misspelled signal handler
(a test on avr-gcc linux)

But why they made it "USART__RXC_vect" instead of "USART_RXC_vect" !!:roll: