These results are based on Timer0 and PIC 18F4550.
But probably will work on yout microcontroller.
Use prescaler and preload.

Prescaler	Preload (16bit)	Why?

    //////////////////////////////////////////////////////
    //
    // Code by PIC Timer Calculator 
    // Developed by Vinícius Lage from Brazil.
    // Email: op.vini@gmail.com
    //
    // Generate a Hz Timer0 interrupt
    //
    //////////////////////////////////////////////////////
    
    #include <18F4550.h>
    #fuses ,NOWDT,PUT,NOBROWNOUT,NOLVP 
    #use delay(clock=)
    
    void main(){
      setup_timer_0( RTCC_INTERNAL | RTCC_DIV_ );
      set_timer0(  ); 
      
      enable_interrupts( INT_TIMER0 );
      enable_interrupts( GLOBAL );
    }
    
    #int_timer0
    void intTimer0(){
      set_timer0(  + get_timer0() ); 
      // put here your code
      // this code will run on the frequecy that you desire 
    }
    

Try other values for frequecy.