Failed to generate 1 second (BASCOM AVR)
===

I had a microcontroller trainer kit that includes ATMEGA8535 and 8MHZ xtal. I want to make simple program that switch off/on led every 1 sec. 
But it wont work, when I run the trainer, the delay seems to be 7 sec. 

here the program with BASCOM AVR. 

    $regfile = "8535def.dat"
    $crystal = 8000000
    
    Config Porta = Output                                       
    
    Config Timer1 = Timer , Prescale = 256    
    Enable Timer1                             
    On Timer1 Isr_von_timer1          
    Enable Interrupts
    Timer1 = 34285                          
    
    Do
    Loop
    End
    
    Isr_von_timer1:                          
    Timer1 = 34285                                            
    Toggle Porta.0                                              
    
    Return

