Power-off test of AT89s52 microcontroller

SMOD: This bit is related to serial port communication. 

　　  SMOD=0; When serial port mode is 1, 2, 3, the baud rate is normal. 

　　  SMOD=1; When serial port mode is 1, 2, or 3, the baud rate is doubled. 

GF1, GF0: Two general working flags, users can use them freely. 

　　  PD: Power-down mode setting bit. 

　　  PD=0 The microcontroller is in normal working state. 

　　  PD=1 The microcontroller enters the power down mode and can be awakened by an external interrupt or hardware reset mode. After entering the power down mode, the external crystal oscillator stops oscillating, the CPU, timer, and serial port all stop working, and only the external interrupt works. 

　　  IDL: Idle mode setting bit. 

　     IDL=0 The microcontroller is in normal working state. 

　　  IDL=1 The MCU enters the idle mode. Except for the CPU, all other parts continue to work. In the idle mode, it can be awakened by any interrupt or hardware reset.

　　　　　　　　　　　　　　　　　　　　　　　　　　  Test circuit diagram

The test procedure is as follows:

#include

#include

sbit key = P3^3; //Key to enter power-down mode

/****************************************

Function name: delay

Function: Delay for a period of time

***************************************/

void delay()

{

 unsigned int i;

 for(i=0;i<30000;i++);

}

/****************************************

Function name: delay20ms

Function: Delay 20ms

***************************************/

void delay20ms(void)     

{

  unsigned char i,j;

  for(i=0;i<100;i++)

   for(j=0;j<60;j++);

}

/****************************************

Function name: init

Function: Initialization program

***************************************/

void init()

{    

 EA=1; //Always enable interrupts

 EX0=1; //Open external interrupt 1

 IT0=1; //Falling edge trigger of external interrupt

}

/****************************************

Function name: keytest

Function: Keyboard program, press the key to enter power-down mode

***************************************/

void keytest()

{

   if(key==0)

 {

  delay20ms();

 if(key==0)

   {

   PCON=PCON|0x02; //Enter power-down mode

  }

  while(!key);

 } 

}

/****************************************

Function name: main

Function: Main function

***************************************/

void main()

{unsigned char aa = 0xfe;

 init();

 while(1)

 {//Realize the running light

  P0=aa;

  aa= _crol_(aa,1);

  delay();  

  keytest(); //Keyboard scan

 }

}

/****************************************

Function name: Int0

Function: interrupt service routine

***************************************/

 void Int0() interrupt 0 using 1

{

 P0=0x00; //All lights are on

 delay();

 delay();

 delay();

}

Experimental results: After the microcontroller is powered on, you can see the running lights rotating; when the key is pressed, the running lights stop and only one light is on; when the key connected to the P3.2 port is pressed, all 8 lights are on, and then the running lights continue to flow in the original position. Moreover, after power failure, the microcontroller is awakened by triggering an external interrupt through the key, the effect is good and it is easy to trigger.

Conclusion: After the AT89S52 microcontroller is awakened from power-down mode by an external interrupt, the external interrupt service program is executed first, and then it returns to the main program interrupt point to continue execution.