Understanding C51 external interrupt (INT0)

To decode the infrared remote control signal, you need to use the C51 external interrupt and set it to the negative transition edge trigger mode. Generally, the interrupt is initialized outside the beginning of the main program (or the initialization interrupt program is written as a function and this function is placed in the main program) as follows:

void main(void)
{

 　IT0=1; //Negative transition trigger
 　EX0=1; //Open external interrupt 0
 　EA=1; //Open general interrupt

　.........//Other programs

　..........
}

void INT0() interrupt 0

{

　.......//Infrared signal decoding program

}

Enable external interrupt as needed (EX0=1):

　The above program opens the external interrupt at the beginning. Theoretically, it is completely correct! But in reality, it depends on the specific situation to open the external interrupt! If you just enter the program to handle other things and cannot process infrared signals temporarily, then EX0=1 cannot be written at the beginning of the main program. It should be written in an appropriate position. Otherwise, when the infrared signal is turned on, it will immediately enter the infrared signal decoding program.

Disable external interrupt (EX0=0):

　Once there is an interrupt signal, the microcontroller will quickly respond to the interrupt and enter the interrupt program. The interrupt program is also the infrared signal decoding program. In the interrupt program, don't forget to turn off the interrupt EX0=0! After pressing a button on the remote control, the remote control will send data out in groups. Even if you press and release the button at the fastest speed, the remote control has sent out multiple groups of data. The microcontroller will decode multiple times. If the main program is relatively large, the decoded data will be overwritten by the next data before it can be used in a hurry! After turning off the external interrupt, it can effectively avoid interference and distinguish whether the current group of data has been received and decoded! When entering the interrupt program, turn off the external interrupt, and turn on the external interrupt after a group of data is decoded and adopted by the main program. This is a complete process! This complete process can be completed normally without interference. In reality, interference is everywhere. Once the data cannot be decoded normally, the main program will not use it, and the external interrupt will no longer be turned on. It will no longer receive infrared signals. At this time, add a judgment at the end of the infrared decoding program. If an error occurs, turn on the external interrupt at the end of the decoding program to prepare for the next infrared signal.

Clear IE0 as needed (IE0=0):

　After the interrupt is turned off, the remote control does not stop sending signals. The infrared signal after the interrupt is turned off will continue to set IE0. The state of IE0 is not controlled by EX0 at all. The single-chip microcomputer executes the IT1=1 statement. As long as the external interrupt has a negative transition edge, IE0 will be set. If we only process the signal after EX0=1 (that is, the signal after the interrupt is turned on), then IE0 must be cleared before the infrared signal decoding program exits. If it is not cleared, as long as the external interrupt is turned on, the interrupt will be entered again. This time, entering the interrupt will waste time at best, and may cause errors (which are very obvious when the infrared decoding uses the query method after entering the interrupt). Therefore, a sentence IE0=0 should be added before EX0=1.