Receiving PUi5 from GSM modem

[mvpradeepemb]

Dear All,

I am interfacing Atmega16 with GSM modem(SIM900). Modem works fine with hyperterminal. Controller also transmits and receives good with hyper terminal. But when i interface controller with gsm, i receive "PU8" and "PUi5" when i transmit "AT" & "AT+CFGM=1".

int main(void)
{
        init();
        lcd_init();
        sei();
        set_timer2();
        ptr=gett;
        usart_init(myubrr);
        step=0;
   
       command(0x01);
       command(0x80);
 
    while(1)
     {



        if (!(PINA & (1<<PINA0)))
                   {
            
                command(0x01);
                command(0x80);     
       if(step==0)
              {
               step=1;
               usart_transmit('A');
               delay(100);
               usart_transmit('T');
               delay(100);
               usart_transmit(13);
              }
       }
               
 if (!(PINA & (1<<PINA1)))
                   {
            
                command(0x01);
                command(0x80);     
        if(step==1)
                {
                 step=2;
                 usart_transmit('A');
                 delay(50);
                 usart_transmit('T');
                 delay(50);
                 usart_transmit('+');
                 delay(50);
                 usart_transmit('C');
                 delay(50);
                 usart_transmit('M');
                 delay(50);
                 usart_transmit('G');
                 delay(50);
                 usart_transmit('F');
                 delay(50);
                  usart_transmit('=');
                 delay(50);
                 usart_transmit('1');
                 delay(50);
                usart_transmit(13);
             
               }
            }
             


   }


}



void init(void)
{

 

  DDRB=0xFF;
  PORTB=0xFF;

 
  PORTC=0xFF;
  DDRC=0xFF;

  DDRA=0x00;
  PORTA=0xFF;

  PORTD=0x00;
  DDRD=0x3C;


}

void delay(const long del)
 {
  long x;
  int y,z;
  for(x=0;x<=del;x++)
   {
     for(y=0;y<=254;y++)
     for(z=0;z<=254;z++);
   }
  return;
 }

void USART_Flush( void )
{
   unsigned char dummy;
   while ( UCSRA & (1<<RXC) ) dummy = UDR;
}

void usart_init(unsigned int ubrr)
{

 UBRRH=(unsigned char)(ubrr>>8);
 UBRRL=(unsigned char)ubrr;
 UCSRB=(1<<RXEN)|(1<<TXEN)|(1<<RXCIE);
 UCSRC = (1 << URSEL) | (1 << UCSZ0) | (1 << UCSZ1); //(1 << URSEL) }

}

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

//unsigned char usart_receiver(void)

ISR(USART_RXC_vect)
{



    rec=UDR;
    display(rec);



}

I also tested using vb6. I transmit chr(10) + chr(13) + "OK" + chr(13) + chr(10) from vb6. I receive $$OK$$ in MCU. But i do know why i am receive PU8 and PUi5 in MCU.