[SOLVED] several interrupts 8051 problem !!

#include<..........>
.
.
.
.
.
main()
{
......
}

void down(void)//down
{

			ES=0; //disable serial ISR
			timer_flag=0;
			ph_sensor_error();
			motor_direction=ANTI_CLOCK_WISE;
			while(ph_sensor_down==OFF && timer_flag==0)
				motor_power=ON;
			motor_power=OFF;
			timer_flag=0;
			ES=1; //enable serial ISR
				
}

void ph_sensor_error(void)
{ 
	TR0 = 1;                      /* Start Timer 1 Running */	
}

/*** timer0 interrupt service routine ***/
void timer0_ISR (void) interrupt 1
{
	TR0 = 0;
	TF0 = 0;
	TH0 = 0x00;              
	TL0 = 0x00;
	counter++;   // Increment the overflow count 
	if(counter>=10)//0.71s
		{
			TR0 = 0;
			TF0=0;
			counter=0;
			timer_flag=1;
		}
	else
		TR0 = 1;

}

/*** serial interrupt ***/ 
void serial_ISR (void) interrupt 4  
{
	unsigned char moh=0;
	if (RI == 1)
    {
    	RI = 0;
		moh=SBUF;
		if(SBUF==0x31)
			down();
	
		    }*/
			
}