8051 MCU - Software Reset

ISP_CONTR: ISP/IAP control register

• SWBS: When set to 0, the software will start from the user application area after reset; when set to 1, the software will start from the ISP program area after reset. This can only be achieved by working directly with SWRST.

• SWRST: When set to 0, no software reset is performed; when set to 1, a software system reset is generated and the hardware is automatically cleared.

This reset resets the entire system. All special function registers will be reset to their initial values ​​and the I/O ports will also be initialized.

[Example] Use a key interrupt to reset the MCU software. After the reset, the LED light flashes for a while, and then the MCU maintains the current state and idles. If you want to continue flashing the LED, you need to reset the MCU.

Software reset code:

1 #include "stc.h"

2

3 #define LED_PORT P2 //Define LED control port as P2

4

5/************************************************

6 *Function name: Delay

7 * Input: None

8 *Output: None

9 *Description: Delay for a period of time

10************************************************/

11 void Delay(void)

12 {

13 unsigned char i,j;

14

15 for(i=0;i<130;i++)

16 for(j=0;j<255;j++);

17 }

18 /************************************************

19 *Function name:SoftReset

20 * Input: None

21 *Output: None

22 * Description: Software reset MCU

twenty three ********************************************/

24 void SoftReset(void)

25 {

26 ISP_CONTR=0x20;

27 }

28 /************************************************

29 *Function name:EXTInit

30 *Input: None

31 *Output: None

32 * Description: External interrupt initialization

33************************************************/

34 void EXTInit(void)

35 {

36 EX1=1; //Enable external interrupt 1

37 IT1=0; //Low level trigger

38 EA=1; //Enable all interrupts

39 }

40 /************************************************

41 *Function name: main

42 * Input: None

43 *Output: None

44 *Description: Function

45************************************************/

46 void main(void)

47 {

48 unsigned char i;

49

50 EXTInit(); //External interrupt initialization

51

52 for(i=0;i<20;i++) //Loop flashing LED light

53 {

54 LED_PORT=~LED_PORT;

55 Delay();

56 }

57

58 while(1)

59 {

60; //No operation

61 }

62 }

63 /************************************************

64 *Function name: EXT1IRQ

65 *Input: None

66 *Output: None

67 * Description: External interrupt 1 interrupt service function reset operation

68 ********************************************/

69 void EXT1IRQ(void)interrupt 2

70 {

71 SoftReset();

72 }

73

Code Analysis:

SoftReset is a reset operation function, which assigns the value of 0x20 to the ISP/IAP control register ISP_CONTR, that is, sets "SWRST" in ISP_CONTR to 1 to perform a software reset. It should be noted that the software reset here is a real reset, which has the same effect as a hardware reset.

In the main function, after initializing the external interrupt, the LED light flashes for a while, and then enters the while(1) infinite loop to perform no operations.

The software reset operation is placed in the external interrupt 1 interrupt service function. As long as the external interrupt 1 is triggered, the microcontroller will be reset.