Catalog

One 、Arduino About timer  

Two 、 The basic concept of timer

Timer speed (HZ) = Arduino Clock speed (16MHz) /  Prescaler coefficients

Interrupt frequency （Hz）=（Arduino Clock speed 16MHz）/（ Preassigned frequency counter *（ Compare matching registers + 1）

Compare matching registers = [16,000,000Hz /( Preassigned frequency counter * Required interrupt frequency )] - 1

3、 ... and 、 Timer configuration code

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 Arduino In the process of learning, we usually use library function operation . But there are no examples of timers . therefore , Here is a brief description of the configuration process of timing interrupt . Reference material ：http://www.instructables.com/id/Arduino-Timer-Interrupts/.

One 、Arduino About timer  

 Arduino UNO There are three timers , Namely timer0,timer1 and timer2. Each timer has a counter , Incrementing at each clock cycle of the timer . Triggered when the counter reaches the value specified in the compare match register CTC Timer interrupt . Once the timer counter reaches this value , It will clear on the next timer of the timer clock （ Reset to zero ）, Then it will continue to count again to compare matches . By selecting the match value and setting the timer to increase the speed of the counter , You can control how often the timer interrupts .

      Next, I will introduce the configuration relationship of each register of the timer . 

Two 、 The basic concept of timer

1、 Prescaled coefficients and comparison matcher

 Arduino Clock with 16MHz function . A scale value of the counter indicates 1 / 16,000,000 second （~63ns）, Run away 1s You need to count 16,000,000.

1、Timer0 and timer2 yes 8 Bit timer , You can store the maximum counter value 255.

2、Timer1 It's a 16 Bit timer , You can store the maximum counter value 65535.

Once the counter reaches its maximum , It will go back to zero （ This is called overflow ）. therefore , We need to divide the clock frequency , The prescaler . The increment speed of the timing counter is controlled by the prescaler . The counting speed of prescaler and timer is as follows ：

Timer speed (HZ) = Arduino Clock speed (16MHz) /  Prescaler coefficients

therefore ,1 The prescaler will be 16MHz Up counter ,8 The prescaler will be in 2MHz Increasing ,64 Preassigned frequency counter = 250kHz, And so on .

The prescaled coefficients of the three timers are shown in table ：

I'll explain in the next step CS12,CS11 and CS10 The meaning of .

Now you can calculate with the following steps Interrupt frequency . The following formula ：

Interrupt frequency （Hz）=（Arduino Clock speed 16MHz）/（ Preassigned frequency counter *（ Compare matching registers + 1）

Rearrange the equations above , Give the interrupt frequency you want , You can solve the comparison register value ：

Compare matching registers = [16,000,000Hz /( Preassigned frequency counter * Required interrupt frequency )] - 1

remember , When you use a timer 0 and 2 when , This number has to be less than 256, about timer1 Less than 65536.

So if you want to interrupt every second （ The frequency is 1Hz）： Compare matching registers = [16,000,000 /( Preassigned frequency counter  * 1)] -1
The prescaler is 1024, You get ： Compare matching registers = [16,000,000 /（1024 * 1）] -1 = 15,624, because 256 <15,624 <65,536, You have to use timer1 To implement this interrupt .

3、 ... and 、 Timer configuration code

int toggle0,toggle1,toggle2=0;

void setup(){
 
  cli();// Turn off global interrupt 
 
  // Set the timer 0 by 10kHz(100us)
  TCCR0A = 0;// Will the whole TCCR0A Register set to 0
  TCCR0B = 0;// Will the whole TCCR0B Register set to 0
  TCNT0  = 0;// Initialize the counter value to 0
  // Set the counter to 10kHZ, namely 100us
  OCR0A = 24;// Compare matching registers = [16,000,000Hz /（ Preassigned frequency counter * Required interrupt frequency ）] - 1
             // Compare matching registers =24, Interrupt interval =100us I.e. interrupt frequency 10khz
  TCCR0A |= (1 << WGM01);// open CTC Pattern 
  TCCR0B |= (1 << CS01) | (1 << CS00); // Set up CS01 Position as 1(8 Multiple prescaler )   
  TIMSK0 |= (1 << OCIE0A);// Enable timer compare interrupt 
  
 
  // Set the timer 1 by 1kHz
  TCCR1A = 0;// Will the whole TCCR1A Register set to 0
  TCCR1B = 0;// Will the whole TCCR1B Register set to 0
  TCNT1  = 0;// Initialize the counter value to 0
  // Set the counter to 10kHZ, namely 1ms
  OCR1A = 15624;//199;// = (16*10^6)/(1000*8) - 1 (must be <65536)
  TCCR1B |= (1 << WGM12);// open CTC Pattern 
  TCCR1B |= (1 << CS12) | (1 << CS10);// Set up CS11 Position as 1(8 Multiple prescaler )
  TIMSK1 |= (1 << OCIE1A);
 
  // Set the timer 2 by 8kHz
  TCCR2A = 0;// set entire TCCR2A register to 0
  TCCR2B = 0;// same for TCCR2B
  TCNT2  = 0;//initialize counter value to 0
  // set compare match register for 8khz increments
  OCR2A = 249;// = (16*10^6) / (8000*8) - 1 (must be <256)
  // turn on CTC mode
  TCCR2A |= (1 << WGM21);// open CTC Pattern 
  // Set CS21 bit for 8 prescaler
  TCCR2B |= (1 << CS21);   
  // enable timer compare interrupt
  TIMSK2 |= (1 << OCIE2A);
 
  sei();// Turn on global interrupt 

  pinMode(13,OUTPUT);
 
}
 
// interrupt 0 Service functions 
ISR(TIMER0_COMPA_vect){
// The generation frequency is 2kHz / 2 = 1kHz Pulse wave of （ The full wave switches to two cycles , Then switch to low ）
  if(toggle0){
    digitalWrite(8,HIGH);
    toggle0 = 0;
  }
  else{
    digitalWrite(8,LOW);
    toggle0 = 1;
  }
}
 
ISR(TIMER1_COMPA_vect){// timer1 interrupt 1Hz Switch pins 13（LED）
// The generation frequency is 1Hz / 2 = 0.5kHz Pulse wave of （ The full wave switches to two cycles , Then switch to low ）
  if(toggle1){
    digitalWrite(13,HIGH);
    toggle1 = 0;
  }
  else{
    digitalWrite(13,LOW);
    toggle1 = 1;
  }
  delay(2000);
}
  
ISR(TIMER2_COMPA_vect){// timer1 interrupt 8kHz Switch pins 9
// The generation frequency is 8kHz / 2 = 4kHz Pulse wave of （ The full wave switches to two cycles , Then switch to low ）
  if(toggle2){
    digitalWrite(9,HIGH);
    toggle2 = 0;
  }
  else{
    digitalWrite(9,LOW);
    toggle2 = 1;
  }
}
 
 
void loop(){
  
}