I am trying to implement a high precision timer using AT89S8252 using the following code: void configureTimer0(void) { EA = 0; TMOD &= 0xf0; TMOD |= 0x01; ET0 =1; TH0 = TH_VAL TL0 = TL_VAL TR0= 1; EA = 1; } // timer 0 interrupt handle void timer0 (void) interrupt 1 { TH0 = TH_VAL; TL0 = TL_VAL; P2_1 = !P2_1; switch(val) { case 1: // code break; case 2: // code break; } } void main(void) { configureTimer0(); while(1); } The problem occurs when I try to insert any code inside the Timer 0 interrupt handle, such as a blinking LED ar a simple switch statement. The code inside interrupt handle was as simple as possible. In order to keep a constant rate, I have to use a digital osciloscope to adjust TH_VAL and TL_VAL. Is there any other way to implement this ? Do I have to constantly calibrate TH_VAL and TL_VAL after inserting any piece of code inside the timer interrupt handle ? Best regards, Andre
Erik: "If the timer interrupt is the only one at the highest priority, your statement above does not apply" I think that is pretty obvious from the first sentence: "Note that if an interrupt of higher priority level goes active..." And please note, that was a quotation from the manual, not my statement. The intention was to correct your inaccurate statement: "1) The interrupts (according to the manual) always execute the fitst instruction." Stefan
Andre, Has any of this been of any help to you? Stefan