51 MCU interrupt setting

External interrupt system block diagram:

The interrupt request flags of these interrupt request sources are latched by the response bits of the special function registers TCON and SCON.

1. TCON register

The lower four bits are related to the interrupt.

1) IT0 and IT1 - external interrupt request trigger flag:

      0——Low level trigger;

     1——Falling edge trigger

    Can be set and cleared by software

2) IE0 and IE1 - external interrupt request flags

     1——Indicates that there is an interrupt request. The CPU will respond to the interrupt request and jump to the interrupt service routine. The interrupt program is processed according to the priority. When jumping into the interrupt service routine, it is cleared to 0 by hardware;

      0——Indicates no interrupt request.

The reset value TCON is always 0.

SCON is the serial port control register, see Serial Port for details.

2. Interrupt enable register IE, bit addressable, reset to 0:

When each bit is 1, the corresponding bit interrupt is enabled, and when it is 0, the corresponding bit interrupt is disabled. EA is the general interrupt switch.

Note: After the microcontroller responds to an external interrupt, it will automatically clear the external interrupt flag to 0. However, due to the characteristics of the external interrupt request triggering method, the problem of repeated requests should be avoided when using external interrupts.

External interrupt 0 programming steps;

1. Set the external interrupt request enable bit and set the EA EX0 bit in the IE register;

2. Select the appropriate external interrupt request mode, that is, set IT0 (or IT1) in TCON;

3. Write the interrupt service function.

Examples:

main()

{

    IT0 = 1; //Set external interrupt 0 to falling edge trigger    
    EX0 = 1; //Open external interrupt 0
    EA = 1; //Open general interrupt
    
  
    while (1) 
        ;
   }
void ext_interrupt(void) interrupt 0 
{
    delay(5);
    if (button0 == 0) {
        led = !led;
    }

}