i am newbie trying to use usart by interrupts in the echo program.
i us atmega 328 and c language.
i have successfully implemented the echo program without using interrupts.
while using interrupt, microcontroller echoes back no character.
here's my program

// program to echo using interrupts
#include<avr/io.h>
#include<util/delay.h>
#include<interrupt.h>
#define BAUD_RATE 9600
#define BAUD_PRESCALE (((F_CPU / (BAUD_RATE * 16UL))) - 1)
void initialise_serial(); //initialise USART
char c;
main()
{
  initialise_serial();
 sei(); 
 UCSR0B |=(1<<RXCIE0);//enabling recieve complete interrupt
  while(1);
  
}

void initialise_serial()
{
  UCSR0B |=(1<<RXEN0)|(1<<TXEN0);
  UCSR0C |=(1<<UCSZ01)|(1<<UCSZ00);
  UBRR0H |=(BAUD_PRESCALE>>8);
  UBRR0L |=BAUD_PRESCALE;
  }
ISR(USART_RXC_vect)
{
  c = UDR0;
  UDR0 =c;
  
}

please help sorting out the problem .
thanks in advance

 

Can you run the debugger, set a breakpoint in the ISR and see if the ISR is being reached?

 

Did you read the datasheet? Check page 184.

 

i am making a transition from arduino ide to programming in pure c.
so, i don't know much about debugging.
could you please offer an alternative??

 

i rechecked the datasheet . i don't seem to find any mistake.

 

A piece of advice. Do things one at a time with increasing difficulty so you know where the mistake might be if things go wrong. First, write simple functions such as putchar and getchar. Then try the echo without interrupt and after that use the interrupts. At page 184 there is this example code:

void USART_Transmit( unsigned char data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRnA & (1<<UDREn)) )
;
/* Put data into buffer, sends the data */
UDRn = data;
}

Did you try this one out? I want you to read the complete section for UART0 in the datasheet attached. Everything is clearly explained there.

 

In the first post the OP did say that he tested the echo program successfully without using interrupts.

To be honest, I have looked over the code and cannot find anything obviously amiss.

 

I did read USART0 chapter.
Still fail to see any problem.
Could there be something wrong in the ISR ??

 

"Writing this bit to one enables interrupt on the RXCn Flag. A USART Receive Complete interrupt
will be generated only if the RXCIEn bit is written to one, the Global Interrupt Flag in SREG is
written to one and the RXCn bit in UCSRnA is set."
Did you do all of these?

 

The sei() macro enables the global interrupt.
The RXCIE0 bit of UCSROB is also enabled.

 

Check to see if you are, indeed, hitting the interrupt vector. I usually use an output initialized to output 0 and set it only in the ISR., this way, a LED can be used to check.

If you do hit the ISR, you know that the error us elsewhere...

 

I followed your advice.
The LED didn't glow.

Replacing RXC by RX in ISR made it work. The source from where I studied it used RXC ,but the datasheet mentioned RX.
But ,now I have another doubt, regarding UDR0 register, which I mention in the next thread.