[avr-libc-dev] Strange behaivour of UART on mega128

[Jon Sjöstedt]

Hello all!
Having worked for some time with the mega128 i have realized that there is
a problem with the UART. Since i can not tell wether this is a hardware or
a software problem, I start by posting you software guys.

The hardware is Bergmann electronics let-at-work.

I run a very simple program to show the problem. The problem is that the
uart sometimes inserts extra zeros in the datastream. The receiver is a
normal PC running FC3.

The problem only happens if the outputted byte is altered. Also, doing
UDR1 = 1; also affects the output on UART0.

The frequency output of the board is stable at 14.7456MHz. This is
measured using oscilloscope and below program

while(1) { PORTA = ~PINA;}

Any ideas?

#include <avr/io.h>

uint8_t i;

int main()
{
  //Configure UART0
  UCSR0A =
    (1<<U2X0)| // Use double UART speed mode
    (0<<MPCM0); // Dont use Multi-procesor communication mode

  UCSR0B =
    (0<<RXCIE0)| // Dont enable RX complete interrupt
    (0<<TXCIE0)| // Dont enable TX complete interrupt
    (0<<UDRIE0)| // Dont enable data register empty interrupt
    (1<<RXEN0)|  // Enable receiver.
    (1<<TXEN0)|  // Enable transmitter.
    (0<<UCSZ02); // Use 8 bit character size

  UCSR0C =
    (0<<UMSEL0)| // Use asynchronous mode
    (0<<UPM01)|  // No parity check
    (0<<UPM00)|  // No parity check
    (0<<USBS0)|  // Use one stop bit
    (1<<UCSZ01)| // Use 8 bit character size
    (1<<UCSZ00); // Use 8 bit character size


  //115200 @14.7456MHz
  UBRR0H = 0; // Use 115200 baud
  UBRR0L = 15; // Use 115200 baud



  while(1)
  {
    i = 255;
    while(!(UCSR0A & (1<<UDRE0)));
    //UDR1 = 1;
    UDR0 = 1;

    while(!(UCSR0A & (1<<UDRE0)));
    i++;
    UDR0 = 255;// = i;

    i++; if (i > 10) i = 1;
  }



  return 0;
}


/Jon