Use Keil2 software to simulate the time of delay statement

First click option for target 'target1' under project

Change the crystal frequency to 11.0592MHz, which is consistent with the crystal frequency on the TX-1C test board

Then click the start/stop debug session button under debug to debug

The delay code is as follows

#include //Int integer variables are allocated two bytes, ranging from (-32768 to 32767, i.e. -2^15 to 2^15-1)

unsigned int i,j; //Unsigned integer variables are allocated two bytes, ranging from (0 to 65535, i.e. 2^16-1)

sbit led8=P1^7; //Declare the highest bit of port P1 as led8

void main()

{

while(1)

{

led8=0; //Set the highest position of P1 port to 0

for(i=100;i>0;i--)

for(j=500;j>0;j--);//It takes time for the MCU to execute the code, and the double-layer for loop plays a role in delaying

led8=1;

for(i=100;i>0;i--)

for(j=500;j>0;j--);

}

}

Click port1 in peripherals

You can see the 8-bit status of P1 port, and all I/O ports are 1

Look at the watch1 label in the lower right corner, press F2, enter the two variables i and j, and it will be displayed as 0x00. i and j are not assigned values ​​at the beginning, and the compiler defaults to 0. They are assigned values ​​after entering the for loop.

You can see that the sec value in the left register window is 422.09 microseconds, which is the time taken by the program from the start to the yellow arrow.

If you run it in a single step, you can see that the check mark in the highest position is gone, indicating that the statement led8=0 has been executed. The eighth diode is lit for 423.18 microseconds, minus 422.09 microseconds, which is 1.09 microseconds, or one machine cycle.

Click the reset button to set two breakpoints. When the full speed runs to the breakpoint, it stops. The statement after the breakpoint is the next statement to be executed.

Click Run at Full Speed, and you can see that the time becomes 88535.16 microseconds. Subtract the previous 423.18, and the double-layer for loop is about 88111.92 microseconds, that is, the eighth LED flashes every 88 milliseconds.

Summarize

1. Clock cycle: The reciprocal of the clock frequency is the reciprocal of the external crystal oscillator. The clock cycle of a 12MHz crystal oscillator is 1/12 microseconds. Machine cycle: A machine cycle consists of 12 clock cycles.

2. In the "New Concept 51 Single Chip Microcomputer Tutorial", the author debugged that when the variable type is unsigned int, the inner for loop is constant at 110. The outer for loop is about the same as the number of milliseconds, such as for(i=1000;i>0;i–)for(j=110;j>0;j–);, which means a delay of 1 second. This is just an approximate time. If you want higher accuracy, use a timer.