How to calculate the delay time in the microcontroller-EEWORLD

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Different types of variables can be used in C programs for delay design. Experimental tests show that using 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.

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--);

}

Keywords：MCU Reference address：How to calculate the delay time in the microcontroller

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