1s delay program design for 51 single chip microcomputer

#include

sbit P1_0 = P1^0;

void Delay(); // The following references must be consistent with the uppercase and lowercase letters here, otherwise there will be warnings or errors

void Main（）

{

while (1) // Start looping

{

P1_0 = 0;

Delay(); // Even if there is no parameter, add () or there will be a Warning

P1_0 = 1;

Delay（）;

}

}

void Delay() // 12M crystal oscillator 1s delay

{

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--); // The last one must have a ;

}

//=======The following is non-code==========//

Principle, using h, i, j, k loop instructions to consume a certain amount of time to achieve delay. Why do we need h, i, j, k four variables in the 12M crystal oscillator delay of 1 second, and the values ​​of each variable are as shown in the above code? This starts with the cycle of the single-chip microcomputer. The single-chip microcomputer has instruction cycle, machine cycle, state cycle, and clock cycle;

Clock cycle: also known as the oscillation period of the crystal oscillator, taking 12MHz as an example, the clock cycle is 1/12000000 = 1/12us;

Machine cycle: 1 machine cycle = 6 state cycles = 12 clock cycles = 1us;

Instruction cycle: The time required for a microcontroller to execute an instruction is called an instruction cycle. The instruction cycle is in machine cycles. Different instructions may require different machine cycles (1-4). A microcontroller takes 1us to execute a single-cycle instruction, 2us to execute a double-cycle instruction, and a for loop takes 8 instruction cycles.

The time consumed by executing the for loop can be measured in Keil through the code:

#include

sbit P1_0 = P1^0;

void Delay（）;

void Main（）

{

while (1) // Start looping

{

P1_0 = 0;

Delay（）;

P1_0 = 1;

Delay（）;

}

}

void Delay（）

{

unsigned char h;

for (h = 1000; h > 0; h--); // breakpoint here

}

The time point after the loop is executed 1000 times

1000 cycles take 0.00042850s - 0.00019600s = 0.00023250s = 232.5us; 1 cycle takes about 0.2us,

1s = 1000000us, 1000000us / 0.2us = 500000 times, and 5 * 4 * 116 * 214 = 496480; because the size of unsigned char is 1 byte and the range is 0~255, we can only get an approximate 1s delay through loop nesting.