Vielen Dank für deine Antwort!
Ich habe deine Vorschläge befolgt.
leider bisher ohne erfolg

Ich nicht genau was du mit "INT0 resp. INT1-Flags nach Anfassen von MCUCSR clearen?" meinst?

und was kann ich anstelle der float's machen?

Vielen Dank!
Chris


der Code im moment:
Code:
#include <inttypes.h> 
#include <avr/interrupt.h>

#define F_CPU 8000000      /* 8Mhz */
#include <util/delay.h>    /* definiert _delay_ms() ab avr-libc Version 1.2.0 */
#include "twimaster.c"

#include "LCD.h"

volatile long t2_y,t2_x;
volatile long t1_y,t1_x;

volatile int x1,x0; // Temp Variablen für adxl und main

int count_y, count_x;


char ziel[5];

ISR(SIG_INTERRUPT1){ 
cli();
  if(x1==1){
    x1=0;				
	if(x0==1) 		MCUCR = (1<<ISC11 | 1<<ISC10 | 1<<ISC01 | 1<<ISC00);
	else MCUCR = (1<<ISC11 | 1<<ISC10 | 1<<ISC01 | 0<<ISC00);
    t1_y = count_y;
  }
  
  else{
    x1=1;			
	if(x0==1)		MCUCR = (1<<ISC11 | 0<<ISC10 | 1<<ISC01 | 1<<ISC00);
	else MCUCR = (1<<ISC11 | 0<<ISC10 | 1<<ISC01 | 0<<ISC00);
    t2_y = count_y;
    count_y = 0;
	}
sei();
}

ISR(SIG_INTERRUPT0){ 
cli();
 if(x0==1){
    x0=0;				
	if(x1==1) 		MCUCR = (1<<ISC01 | 1<<ISC00 | 1<<ISC01 | 1<<ISC00);
	else MCUCR = (1<<ISC01 | 1<<ISC00 | 1<<ISC01 | 0<<ISC00);
    t1_x = count_x;
  }
  
  else{
    x0=1;				
	if(x1==1)		MCUCR = (1<<ISC01 | 0<<ISC00 | 1<<ISC01 | 1<<ISC00);
	else  MCUCR = (1<<ISC01 | 0<<ISC00 | 1<<ISC01 | 0<<ISC00);
    t2_x=count_x;
    count_x = 0;
  }
sei();
}

ISR (SIG_OUTPUT_COMPARE1A){
count_y++;
count_x++;
}  

void Timer_Inits(void){

    TCCR1A = 0;
    TCCR1B = (1 << WGM12) | (1 << CS10); 
  
  	OCR1A = (uint16_t) ((uint32_t) F_CPU / 50000); //100000

    TIMSK |= (1 << OCIE1A); 	// Interrupt wenn Timer Vergleichswert erreicht

 	GIMSK = (1<<INT0 | 1<<INT1);		//Int0,1 aktiv
//	GIMSK = (1<<INT1);		//Int0,1 aktiv

} 

int main (void){
	DDRC = 0x00;    //alles als Eingan def.
	PORTC =0x00;	//PullUp's aus

	DDRD  =0x00;	//alles Eingang
	PORTD =0x00;	//PullUp's aus
	
	Timer_Inits();
	sei();
	i2c_init(); 
	_delay_ms(10000);
	lcd_init();
	_delay_ms(10000);

for(;;){

_delay_ms(90000000);_delay_ms(90000000);_delay_ms(90000000);
clear();


int result;

(int)result = (((((float)t1_y/(float)t2_y)*1000)-481)*1000)/125;

sprintf(ziel,"%d",result);
stringout ("a_y=");
stringout (ziel);

result = (((((float)t1_x/(float)t2_x)*1000)-481)*1000)/125;
sprintf(ziel,"%d",result);
stringout (" a_x=");
stringout (ziel);


//	if(result>4)	PORTC|=(1<<PC3); //LED2 anschalte

//	else   PORTC&=~(1<<PC3); 
//	if(result>6000)	PORTC|=(1<<PC2); //LED1 anschalte
//	else   PORTC&=~(1<<PC2); 

//	if(result>7)	PORTC|=(1<<PC1); //LED0 anschalte
//	else   PORTC&=~(1<<PC1); 

//	if(result>8)	PORTC|=(1<<PC0); //LED0 anschalte
//	else   PORTC&=~(1<<PC0); 
   }
}