About the 1ms delay program for STC89C52 microcontroller?

cpfpost

About the 1ms delay program for STC89C52 microcontroller? [Copy link]

Regarding the delay program of the STC89C52 microcontroller, the crystal oscillator is 12MHz, and the machine cycle is 1us. The program is as follows:

void Delay1ms() //@12.000MHz

{

unsigned char i, j;

i = 2; //1us

j = 239; //1us

do

{

while (--j);

} while (--i);

}

Delay time calculation: 497*2+1+1+2+2=1000us=1ms

The loop body is executed 497 times, which is 497 machine cycles. I don't understand why it needs to be multiplied by 2. Please tell me in more detail.

peq200

You can generate this directly using the software on the STC official website. No need to be so troublesome.

cpfpost

peq200 posted on 2020-8-22 10:33 You can generate this directly using the software on the STC official website. No need to be so troublesome.

This is what the software generated, but I don't quite understand it.

aallian

Looking at the assembly, you can see that 497 is the execution cycle of while(--j), and it is multiplied by 2 because of the two loops of while(--i).

freebsder

The instruction time is fixed, and the number of instructions occupied by one cycle or two cycles is also fixed. You can find out this number by calculating it based on the frequency set by your ISP.

damiaa

do
{
     while (--j);
}while (--i);
先看
do
{
     。。。。
}while (--i);

 其次while (--j);
do
{
     。。。。
}while (--i);只是里面的内容

其实这样也很好啊：
while (i--)
{
     while (--j);
};

void DelayXms(unsigned int t) //@12.000MHz
{
    for(k=0;i<t;k++)
    {
        unsigned char i=2, j=239;
        while (i--){ while (--j); };
    }
}

huo_hu

Two cycle instructions

huo_hu

Compile it and look at the assembly code