rpm with pic 877

unsigned int TimerOverFlow;
float countLeft,TimerTimeLeft,TotalTimeTaken,RPM,x;

static void interrupt isr()
{
	if(INTF)
	{
		if(TMR1ON==0)
		{
			TimerOverFlow=0;
			TMR1H=0xFB;
			TMR1L=0x1D;
			TMR1ON=1;
		}
		else
		{
			TMR1ON=0;
			INTE=0;
			countLeft=(TMR1H*256+TMR1L)-0xFB1D;
			TimerTimeLeft=countLeft/125000;
			TotalTimeTaken=TimerOverFlow*0.01+TimerTimeLeft;
			x=countLeft;
			RPM=60/TotalTimeTaken;
			TimerOverFlow=0;
			TMR1H=TMR1L=0;
			INTE=1;
			TMR1ON=1;
		}
		INTF=0;
	}
	if(TMR1IF)
	{
		TMR1H=0xFB;
		TMR1L=0x1D;
		TimerOverFlow++;
		TMR1IF=0;
	}
}

//////////////////////////////////

void main(void){
	unsigned RPMReadingHold;
	TRISA = TRISC = 0x00;
	PORTA = PORTC = 0x00;

	INTCON=0xC0;
	INTE=1;
	T1CON=0X30;
	TMR1H=0xFB;
	TMR1L=0x1E;
	INTEDG=1;