Beim Interrupt Variable in die main übergeben

#define F_CPU 12000000

#include <inttypes.h>

#include <stdint.h>

#include <avr/io.h>

#include <avr/interrupt.h>

#include <util/delay.h>

#include "lcd-routines.h"

#define BAUD 9600

#define MYUBRR F_CPU/16/BAUD-1

#define CTS (PINB & 1)

/*Funktionsprototypen*/

void USART_Transmit( unsigned char data );

void USART_Init( unsigned int ubrr);

void Schreibe_in_Binaer(unsigned char test);

/*globale Variablen*/

unsigned char receive_old=0;

volatile unsigned char receive=1;

/*Interrupt*/

ISR(USART_RXC_vect)

{

  receive = UDR;

  lcd_setcursor(0,1);

  Schreibe_in_Binaer(receive);

}

/*Hauptprogramm*/

int main(void)

{

  DDRD = 0xF0;

  lcd_init();

    USART_Init( MYUBRR);

  sei();

  while(1)

  {

    /*Lauflicht*/

    PORTD = 0x80;

    _delay_ms(400);

    PORTD = 0x40;

    _delay_ms(200);

    PORTD = 0x20;

    _delay_ms(200);

    PORTD = 0x10;

    _delay_ms(400);

    PORTD = 0x20;

    _delay_ms(200);

    PORTD = 0x40;

    _delay_ms(200);

    USART_Transmit(0x53);

    //Befehl wird empfangen

    lcd_setcursor(0,2);

    Schreibe_in_Binaer(receive);

  }

  return 0;

}

void USART_Init( unsigned int ubrr)

{

/* Set baud rate */

UBRRH = (unsigned char)(ubrr>>8);

UBRRL = (unsigned char)ubrr;

/* Enable receiver and transmitter */

UCSRB = (1<<RXEN)|(1<<TXEN)|(1<<RXCIE)|(1<<TXCIE);

/* Set frame format: 8data, 1stop bit */

UCSRC = (1<<URSEL)|(3<<UCSZ0);//(1<<USBS)|

}

void USART_Transmit( unsigned char data )

{

/* Wait for empty transmit buffer */

while ( (!( UCSRA & (1<<UDRE)))|| CTS )

;

/* Put data into buffer, sends the data */

UDR = data;

}

//Ausgabe eines Bytes in Binärem Code

void Schreibe_in_Binaer(unsigned char test)

{

  int i;

  unsigned char schreib[9];

  for(i=0; i<8; i++)

  {

    if (test & 1<<(7-i))

    {

      schreib[i] = '1';

    }

    else

    {

      schreib[i] = '0';

    }

  }

  schreib[8]=0;

  lcd_string( schreib);

}