Callback

1. Callback TYWu

2. Reference and Library • Reference • http://www.arduino.cc/playground/Code/Timer1 • Download Library • http://code.google.com/p/arduino-timerone/downloads/detail?name=TimerOne-v9.zip&can=2&q= • Unzip the downloaded file in …arduino-1.0.4\libraries\TimerOne

3. TimerOne.h • initialize(period) • You must call this method first to use any of the other methods. You can optionally specify the timer's period here (in microseconds), by default it is set at 1 second. Note that this breaks analogWrite() for digital pins 9 and 10 on Arduino.

4. Template #include "TimerOne.h"  void setup() {   Timer1.initialize(500000);         // initialize timer1, and set a 1/2 second period   Timer1.attachInterrupt(callback);   // attaches callback() as a timer overflow interrupt }

5. Template (Cont’d) void callback() {   //callback statements } void loop() { // your program here... }

6. Example #include "TimerOne.h"  unsigned long time; void setup() {   Timer1.initialize(500000);           Timer1.attachInterrupt(callback); Serial.begin(9600); time = millis(); }

7. Example (Cont’d) void callback() { Serial.println(millis() - time);   time = millis(); } void loop() { }

8. attachInterrupt() • attachInterrupt() • Specifies a function to call when an external interrupt occurs. • Replaces any previous function that was attached to the interrupt. • Most Arduino boards have two external interrupts: numbers 0 (ondigital pin 2) and 1 (on digital pin 3)

9. attachInterrupt() • The table below shows the available interrupt pins on various boards.

10. attachInterrupt() • Syntax attachInterrupt(interrupt, function, mode) attachInterrupt(pin, function, mode) (Arduino Due only) • interrupt: the number of the interrupt (int) • function: the function to call when the interrupt occurs; this function must take no parameters and return nothing. This function is sometimes referred to as an interrupt service routine. • mode: defines when the interrupt should be triggered. Four contstants are predefined as valid values: • LOW to trigger the interrupt whenever the pin is low, • CHANGE to trigger the interrupt whenever the pin changes value • RISING to trigger when the pin goes from low to high, • FALLING for when the pin goes from high to low.

11. attachInterrupt() • Example int pin = 13; volatile int state = LOW; void setup() {  pinMode(pin, OUTPUT);   attachInterrupt(0, blink, CHANGE); } void loop() {    digitalWrite(pin, state); } void blink() { delay(1000);  state = !state; }

12. attachInterrupt() If pin 2 changes its value…. What'shappened?

13. Lab • Lab Interrupt