View source for Lesson 21--Microduino "Use Timer Interrupt"

{{Language|Microduino_定时器中断的使用}}
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==Objective==
This lesson will introduc Microduino's timer interrupt. Use the timer interrupt to control LED by IO port 13. The time slot is 500ms.
==Equipment==
'''[[Microduino-Core]]'''
'''[[Microduino-FT232R]]'''
*Other hardware equipment
**Breadboard Jumper            one box   
**Breadboard  	               one piece  
**LED                          one 
**220Ω resistor     	         one 
**USB Data cable               one

==Experiment 1==

===Use library MsTimer2===

*Download MsTimer2 library：'''[[File:MsTimer2.zip]]'''

*Example：
<source lang="cpp">
// LED connects to Pin 13
#include <MsTimer2.h>               //Timer's head file

void flash()                        //The interrupt service function
{                        
  static boolean output = HIGH;
  digitalWrite(13, output);
  output = !output;
}
void setup()
{
  pinMode(13, OUTPUT);
  MsTimer2::set(500, flash);        //Set interrupt function, the timer is 500ms
  MsTimer2::start();                //Start timer
}

void loop()
{
}
</source>

===Result===
The state of LED changs every 500ms.

==Experiment 2==

===Use function millis()===

*Example program

<source lang="cpp">
unsigned long ledOn=500,ledOff=500; //Define the timer 500ms
int ledStatus;                      //Define LED state, HIGH or LOW
void setup()
{
	pinMode(13,OUTPUT);
	digitalWrite(13,HIGH);
	ledStatus=HIGH;
}
void loop()
{
    unsigned long nowtime=millis(); //Get the system current runned time
    if(ledStatus==HIGH)             //Check LED state
    {
      if(nowtime>ledOn)             //Check if time out happened
      {
        ledOn=nowtime;              //Record time, the first time is 500ms
        ledOff=nowtime+500;         //Calculate next time when LED state change
        digitalWrite(13,LOW);       //LED off
        ledStatus=LOW;              //Record current LED state, used next time     
    }
}

else{      
	if(nowtime>ledOff)
	{   
		ledOff=nowtime;
		ledOn=nowtime+500;
		digitalWrite(13,HIGH);
		ledStatus=HIGH;
	}
}
}
</source>

===Result===
*Use the function mills()has the same result. LED state changed every 500ms.

*Function mills() can achieve the functionality of interrupt. The function of mills() is to obtain the system running time length, and the unit is ms. Up range is 9 hours 22 minutes, if beyond this time slot will start from zero. The return value of a function is unsigned long type.

*Players can use function mills() according to actual situation. The advantages of using function mills()is that take up the entire program running time is short, if use time delay function, in the delay time, the CPU can't do anything else.

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