getting junk data/ characters on atmega8 RX

[sherazi]

i am using two Atmega8 to communicate with each other using UART , but i am having problems at the receiver side, it gets some data all the time, even if the wire on another side is not connected . if i remove the wire it doesn't, have changed wires and even the circuit, had built three times on separate boards, but same problem is occurring, have checked the code and circuit using Proteus its all OK.

receiver code:

#include <avr/io.h>
#include <util/delay.h>




#if !defined (F_CPU)
#define F_CPU 1000000
#endif

//#define RAMSTART 0x0060
//#define RAMSIZE (RAMEND-RAMSTART)

#define sleep()




// --------------
// --- USART0 ---
// --------------

void USART0_Transmit(unsigned char data)
{
	while (!(UCSRA & (1<<UDRE))) ;
	UDR = data;
}
void USART0_TransmitString(char *data)
{
	while (*data) USART0_Transmit(*data++);
}
unsigned char USART0_Receive(void)
{
	while (!(UCSRA & (1<<RXC))) ;//sleep();
	return UDR;
}
void USART0_Init(void)
{
	// USART0 settings: 2400 baud 8-n-1
// WARNING: real baud = 9615: err = 0.156249999999991%
	UBRRH = 0;
	UBRRL = 25;
	UCSRB |= (1 << RXEN) | (1 << TXEN); 
	UCSRC = (1<<UCSZ1) | (1<<UCSZ0)|(1<<URSEL);
}




// -------------
// --- ports ---
// -------------

void Ports_Init(void)
{
	DDRB = 255; // iiiiiiii
	PORTB = 255; // iiiiiiii
	DDRC = 255; // -iiiiiii
	PORTC = 255; // -iiiiiii
	DDRD = 2; // iiooooii
	PORTD = 0; // iiiiiiii
}


int main()
{
	Ports_Init();
	PORTB=0xfe;
	
	
	_delay_ms(200);
	
	_delay_ms(200);
	PORTB=0;
	_delay_ms(200);
	_delay_ms(200);
	PORTB=0xfe;
	
	_delay_ms(200);
	_delay_ms(200);

	PORTB=0;
	
	_delay_ms(200);
	_delay_ms(200);
	
	PORTB=0xfe;
	USART0_Init();
	//sei(); // enable interrupts
char a;
uint8_t b,x,y,z;
b=1;
x=1;
y=1;
z=1;
int i=2;

    while(1)
	{
	
		
		abc:
		 a=USART0_Receive();
		if (a=='m')
		{
			a=USART0_Receive();
			if (a=='e')
			{
				a=USART0_Receive();
				if (a=='p')
				{
					a=USART0_Receive();
					if (a=='r')
					{
						
						a=USART0_Receive();
						if (a=='8')
						{
							PORTB^= 1 << 2;					
						}
						else if (a=='2')
						{
							PORTB^= 1 << 3;
						}
						else if (a=='3')	
						{
							
							PORTB^= 1 << 4;
							
						}	
						 else if (a=='9')	
						{
							
							i++;
							if(i%2==0)
							PORTB=255;
							else 
							PORTB=0;						
							
							
						}	 
						goto abc;
					}
					 
					else goto abc;	
				}
				else goto abc;
			}
			else goto abc;	
		}																							
		else goto abc;
	}
	 
	
}

and transmitter code

//TRANSMITTER :

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>


#if !defined (F_CPU)
#define F_CPU 1000000
#endif

//#define RAMSTART 0x0060
//#define RAMSIZE (RAMEND-RAMSTART)





// --------------
// --- USART0 ---
// --------------

void USART0_Transmit(unsigned char data)
{
	while (!(UCSRA & (1<<UDRE))) ;
	UDR = data;
}
void USART0_TransmitString(char *data)
{
	PORTB=0;
	_delay_ms(100);
	while (*data) USART0_Transmit(*data++);
	PORTB=255;
}
unsigned char USART0_Receive(void)
{
	while (!(UCSRA & (1<<RXC))) ;//sleep();
	return UDR;
}
void USART0_Init(void)
{
	// USART0 settings:  baud 8-n-1
// WARNING: real baud = 9615: err = 0.156249999999991%
	UBRRH = 0;
	UBRRL = 25;
	UCSRB |= (1 << RXEN) | (1 << TXEN); 
	UCSRC = (1<<UCSZ1) | (1<<UCSZ0)|(1<<URSEL);
}



// -------------
// --- ports ---
// -------------

void Ports_Init(void)
{
	DDRB = 0xff; // iiiiiiii
	PORTB = 0xff; // iiiiiiii
	DDRC = 0; // -iiiiiii
	PORTC = 0; // -iiiiiii
	DDRD =  2; // iiooooii
	PORTD = 0; // iiiiiiii
}


int main()
{
	Ports_Init();

	USART0_Init();
	//sei(); // enable interrupts
	PORTB=0xfe;
	
	
	_delay_ms(200);
	
	_delay_ms(200);

	PORTB=0;
	_delay_ms(200);
	_delay_ms(200);

	PORTB=0xfe;
	
	_delay_ms(200);
	_delay_ms(200);

	PORTB=0;
	
	_delay_ms(200);
	_delay_ms(200);
	
	PORTB=0xfe;

    while(1)
	{
		
		uint8_t a;
		a=PIND;
		a&=0x40;
		if(a==0)
		{
			do{
			a=PIND;
			a&=0x40;
			}	
			while (a==0);	
			
			USART0_TransmitString("mepr9");


		}
		a=PIND;
		a&=0x10;
		if(a==0)
		{
			do{
			a=PIND;
			a&=0x10;
			}	
			while (a==0);
			USART0_TransmitString("mepr2");
			
		}
		a=PIND;
		a&=0x08;
		if(a==0)
		{
			do{
			a=PIND;
			a&=0x08;
			}	
			while (a==0);
			USART0_TransmitString("mepr8");
			

		}
		a=PIND;
		a&=0x20;
		if(a==0)
		{
			do{
			a=PIND;
			a&=0x20;
			}	
			while (a==0);
			USART0_TransmitString("mepr3");
			

		}
	}
	return 0;
}

 

[ckshivaram]

common ground between the two boards is a must which i dont see?????????

 

[sherazi]

have tried that also still same problem , tried to operate with one source also

 

[ckshivaram]

first connect the transmitting board to hyperterminal and see if you get correct data.... then connect the receiving board to hyperterminal and send some data from terminal window and see where the problem exists.....................

 

[sherazi]

dont have the max323 ic now ...
will get it in two days ... wish i get a solution befor that

 

[ckshivaram]

use max 232 not 323 or its series....

 

[sherazi]

sorry just miss typed that !

 

[bigdogguru]

Have you switched the roles of the MCUs? Is the outcome the same, the MCU in the role of the RX is still receiving spurious input?

Whether it is the cause of the problem or not, as chshivaram mentioned, a common ground is an absolute must, especially when you implement the MAX232s. You'll easily have voltages in the +/- 12V or higher range, more than enough to fry the ATMEGAs.