Interfacing 2 serial devices using interrupt method

////////////////// ///////////////////////////////////////// /////////////////////////////
////////////////////////////// START SOFTWARE UART /////////////////////////////////////
///////////////////////////////////// ///////////////////////////////////////// //////////
unsigned char baud_delay_one=216;//this variable are only used for tune baudrate
unsigned char baud_delay_one_and_half=184;//this variable are only used for tune baudrate
char bit_count=0;
char uart_rx_byte=0;
char uart_status=0;
#define idle 0
#define transmitting 1
#define receiving 2
#define received_data_pending 3
#define start_bit 4
void init_timer0(){ //TIMER0 initialize for software uart
   TIMSK |= (1<<TOIE0); //ENABLE 0-TIMER0 OVERFLOW INTERRUPT
   TCCR0 = (0x04); //NORMAL MODE,INTERNAL CLK,PRESCALER=1:256
   TCNT0=baud_delay_one;       //1 bit length for 9600bps (104us) at 12Mhz crystal
   sei();                   // Interrupt Enabled GLOBALLY
}
ISR(TIMER0_OVF_vect) {
   unsigned char sreg = SREG;
   cli();                       // Disable Global interrupt
   TCNT0=baud_delay_one;                   //1 bit length for 9600bps (104us) at 12Mhz crystal
   bit_count++;
   SREG = sreg;
}
void uart_send_byte(char send_byte){
   TCNT0=baud_delay_one;
   bit_count=0;
   while(1){
       if(bit_count==0){output_port4 &=~(1<<utx);}
       if((bit_count>0) && (bit_count<9)){
           if(send_byte & (1<<(bit_count-1))){output_port4 |= (1<<utx);} else{output_port4 &=~(1<<utx);}
       }
       if(bit_count==9){output_port4 |= (1<<utx);}
       if(bit_count>9){break;}
   }
}

void uart_sent_string(char send_string[]){
   unsigned char i=0;                       // iterating variable
   unsigned char LENGHT = 0;// length of the word
   for(i=0;i<500; i++){
       if(send_string[i] == ''){
           break;
       }
       LENGHT++;
   }
   i=0;
   while(i<LENGHT){uart_send_byte(s end_string[i]);i++;}
}

#define output_ddr DDRD
#define output_port4 PORTD
#define utx 3
//in main()
//initialize this port

init_timer0();//this to create baud rate by overflow interrupt
output_ddr |= (1<<utx);//as output port
output_port4 |= (1<<utx);//pull up because in idle time uart tx line is high

while(1 ){//main while
uart_sent_string("testing transmitter of software uart");// this will send out and you can see it on pc terminal
_delay_ms(1000);
    }
///////////////////////////////////// ///////////////////////////////////////// //////////
//////////////////////////////// END SOFTWARE UART /////////////////////////////////////
///////////////////////////////////// ///////////////////////////////////////// //////////

Above code is made for avr microcontroller and its crystal 12Mhz. for any doubt, ask me in comment below.

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Interfacing 2 serial devices using interrupt method