MCU Basics (VI): MCU Timing/Controller Control Interface

Control interface of microcontroller timer/controller

5 Steps to Timer/Event Counter Programming

1. Select the working mode according to the requirements, determine the mode control word, and write it into the TMOD register

2. Calculate the count value of the timer/counter, find the initial count value, and write it into the initial value register

3. Open the interrupt option of the timer/counter as needed

4. Set the timer/counter control register TCON and start the timer

5. Wait for the timing time to expire and use query or interrupt mode to handle the situation accordingly

Timer/Counter Application Examples

  The basic idea of ​​using timers to generate periodic actions:

Generate periodic timing

When the scheduled time comes, take corresponding measures

 For example, if the system clock frequency is 12MHz, the timer/counter T0 is required to output a square wave with a period of 500μs from P1.0 (i.e., periodic high and low level switching).

analyze:

  To output a square wave with a period of 500μs from P1.0, it is only necessary to invert P1.0 every 250μs.

  When the system clock is 12MHz, the oscillation frequency is (1/12M)s, that is, (1/12)μs. One machine cycle is 12 oscillation cycles, so one machine cycle is 1μs, that is, one count is 1μs, then the count value is 250, select counting mode 2, and the initial count value is 256 of mode 2 - 250 = 6

  Working mode 2, mode control word 0x02, count initial value 6, TH0 = TL0 = 0x06

Code

Query method: always query the status of TF and handle overflow

/*

*12MHz crystal oscillator makes the P1.0 port output a square wave with a period of 500μs

*/

#include

sbit P1_0 = P1^0;

void main(){

TMOD = 0x02;

TH0 = TL0 = 0x06;

TR0 = 1;

for(;;){

if(TF0){//Query overflow status

TF0 = 0; //Home

P1_0 = ~P1_0; //Processing

}

}

}

Interrupt method: The overflow state triggers an interrupt, and the interrupt service is used to handle the overflow

#include

sbit P1_0 = P1^0;

void main(){

TMOD = 0x02;

TH0 = TL0 = 0x06;

EA = 1; //

ET0 = 1; //Interrupt control, see the interruption chapter of this series of blogs for details

TR0 = 1;

while(1); //Keep the program running

}

//Interrupt service routine

void time0_int(void) interrupt 1 {

P1_0 = !P1_0;

}

Long time timing

  Generally, the crystal frequency is in MHz, and the machine cycle is in μs. Such a short cycle sometimes cannot meet the needs, but we can use programming to achieve longer timing, such as setting a count variable, and adding one to the count variable every 100μs. When the count variable reaches 10000, the timing of 1s is achieved. This can flexibly adapt to the needs