Briefly describe the delay function of 51 single chip microcomputer

Different types of variables can be used in C programs for delay design. After experimental testing, the use of unsigned char type has more optimized code than unsigned int. Unsigned char should be used as a delay variable when used. Take a microcontroller with a crystal oscillator of 12MHz as an example. The crystal oscillator is 12MHz, which means that one machine cycle is 1us. Extended reading: Detailed explanation of the assembly delay program algorithm

1. 500ms delay subroutine

program:

void delay500ms(void)

{

unsigned char i,j,k;

for(i=15;i>0;i--)

for(j=202;j>0;j--)

for(k=81;k>0;k--);

}

Calculation:

The program has three layers of loops

One layer of loop n: R5*2 = 81*2 = 162us DJNZ 2us

Second layer loop m: R6*(n+3) = 202*165 = 33330us DJNZ 2us + R5 assignment 1us = 3us

Three-layer loop: R7*(m+3) = 15*33333 = 499995us DJNZ 2us + R6 assignment 1us = 3us

Outside the loop: 5us, subroutine call 2us + subroutine return 2us + R7 assignment 1us = 5us

Total delay time = three-layer loop + outside loop = 499995+5 = 500000us = 500ms

Calculation formula: Delay time = [(2*R5+3)*R6+3]*R7+5

2. 200ms delay subroutine

program:

void delay200ms(void)

{

unsigned char i,j,k;

for(i=5;i>0;i--)

for(j=132;j>0;j--)

for(k=150;k>0;k--);

}

3. 10ms delay subroutine

program:

void delay10ms(void)

{

unsigned char i,j,k;

for(i=5;i>0;i--)

for(j=4;j>0;j--)

for(k=248;k>0;k--);

}

4. 1s delay subroutine

program:

void delay1s(void)

{

unsigned char h,i,j,k;

for(h=5;h>0;h--)

for(i=4;i>0;i--)

for(j=116;j>0;j--)

for(k=214;k>0;k--);

}

Regarding the precise delay of the microcontroller C language, many functions on the Internet only give an approximate delay value without an exact value, and thus fail to meet the high precision requirements. This function overcomes the above shortcomings and can accurately count the delay value to within 1us. The CPU used in this example is the STC12C5412 series 12x speed microcontroller. It can be used in other series of microcontrollers as long as the parameter value is modified, and has a wide range of applications.

There are three delay functions as follows:

Function calls are divided into two levels: the first level is a delay of less than 10US, and the second level is a delay of more than 10US.

//====================Less than 10US【use 1US level delay】====================

//----------Microsecond delay---------

for(i=X;i>X;i--) delay time=(3+5*X)/12 Tips (unit: us, X cannot be greater than 255)

//================Greater than 10US and less than 21.9955Ms can use [10US level delay function]===========

void Delay10us(uchar Ms)

{

volatile data i;

for(;Ms>0;Ms--)

for(i=26;i>0;i--);

}

i=[(delay value-1.75)*12/Ms-15]/4

If you want to delay for 60US, then i=[(60-1.75)*12/6-15]/4=25.375≈26; modify the value of i = 26, and then call the above [10US level delay function] Delay10us(6); then the delay will be exactly 60US;

If you want to delay 64us, you can use these two functions in combination: Delay10us(6); for(i=9;i>X;i--) Total delay 64us