การเขียนโปรแกรมเบื้องต้นกับ Arduino (การส่งข้อมูลแบบ I2C)

การสื่อสารข้อมูลด้วยระบบบัส I2C

Arduino Sketch

//////////////////////////////////////////////////////////////////////////
// Author: RSP @ ESL (Embedded System Lab), KMUTNB
// Date: 2014-APR-10
// Target Board: Arduino (ATmega328P, 5V, 16MHz)
// Arduino IDE: version 1.0.5
// Description:  
//   This Arduino sketch demonstates how to implement either
//   a master or a slave device for the I2C bus using Arduino boards.
//   Two Arduino boards are required, one for the master and
//   one for the slave.
//   To build the Arduino sketch for the I2C master, MASTER must be 
//   defined in the code. For the I2C slave, SLAVE must be defined.
//   This example uses 0x74 as the I2C slave address. 
//   The speed rate is at 400kHz. Internal pull-up resistors are
//   disabled. External pull-up registers (4.7k or 2.2k) are required.
//
//////////////////////////////////////////////////////////////////////////

#include <Wire.h> // use the Wire library

//-----------------------------------------------------------------

//#define SLAVE

#define I2C_ADDR  (0x74) /* 7-bit I2C address of the slave device */
#define LED_PIN   (13)   // LED pin

#if !defined(SLAVE) && !defined(MASTER)
 #define MASTER
#endif

#if defined(SLAVE) && defined(MASTER)
 #error "Please do not define both MASTER and SLAVE."
#endif

//-----------------------------------------------------------------
#ifdef SLAVE

byte data = 0;

// This function will be called when the slave device receives
// a transmission from a master.
void i2c_recv_event( int numBytes ) {
  // expect only one byte to be read
  data = Wire.read(); // read only byte
}

// This function will be called when a master requests data from this slave device.
void i2c_send_event( ) {
  digitalWrite( LED_PIN, HIGH );
  Wire.write( data ); // send only one byte
  digitalWrite( LED_PIN, LOW );
}

// Uno or 328P:  A4 for SDA and A5 for the SCL line of the I2C bus.
void setup() {
  pinMode( LED_PIN, OUTPUT );
  Serial.begin( 115200 ); // set baudrate
  Wire.begin( I2C_ADDR );  
  TWBR = 12; // use 400kHz instead of 100kHz
  
  // Note: The default Wire library enables the internal pullup resistors. 
  // Disable internal pull-up resistors on SDA and SCL.
  //pinMode( SDA, INPUT );
  //pinMode( SCL, INPUT );
  digitalWrite(SDA, 0);
  digitalWrite(SCL, 0);
  
  // register the handlers for I2C events
  Wire.onReceive( i2c_recv_event );
  Wire.onRequest( i2c_send_event ); 
}

void loop() {
  // empty
}

#endif // SLAVE

//----------------------------------------------------------------
#ifdef MASTER

byte data = 0; 
char sbuf[32];

void i2c_scan() {
  int count = 0;
  Serial.println( "Scanning I2C slave devices..." );
  for( byte addr=0x01; addr <= 0x7f; addr++ ) {
     Wire.beginTransmission( addr ); 
     if ( Wire.endTransmission() == 0 ) {
       sprintf( sbuf, "I2C device found at 0x%02X.", addr );
       Serial.println( sbuf );
       count++;
    }
  }
  if (count > 0 ) {
    sprintf( sbuf, "Found %d I2C devices.", count );
  } else {
    sprintf( sbuf, "No I2C device found." );
  }
  Serial.println( sbuf );
}

void test_write_read( byte value ) {
  sprintf( sbuf, "Master: 0x%02X sent.", data );
  Serial.println( sbuf );

  Wire.beginTransmission( I2C_ADDR );
  Wire.write( value ); // write one byte
  Wire.endTransmission();
  
  delayMicroseconds(10);

  digitalWrite( LED_PIN, HIGH );
  Wire.beginTransmission( I2C_ADDR );
  Wire.requestFrom( (uint16_t)I2C_ADDR, 1 ); // read one byte
  digitalWrite( LED_PIN, LOW );

  if ( Wire.available() == 1 ) {
    byte data = Wire.read();
    sprintf( sbuf, "Master: 0x%02X received.", data );
    Serial.println( sbuf );
  } else {
    Serial.println( "Master: error!" );
  }
  Wire.endTransmission();
}

// Uno or 328P:  A4 for SDA and A5 for the SCL line of the I2C bus.
void setup() {
  Serial.begin( 115200 );
  Wire.begin();  
  TWBR = 12; // use 400kHz instead of 100kHz
  pinMode( LED_PIN, OUTPUT );
  
  // Note: The default Wire library enables the internal pullup resistors.
  // Disable internal pull-up resistors on SDA and SCL
  //pinMode( SDA, INPUT );
  //pinMode( SCL, INPUT );
  digitalWrite(SDA, 0);
  digitalWrite(SCL, 0);
  delay(100);
  //i2c_scan(); // perform I2C device scanning
  delay(2000);
}

void loop() {
  test_write_read( data );
  data++;
  delay(500);
}

#endif // MASTER

//////////////////////////////////////////////////////////////////////////

   Master        Slave  
   A4 (SDA) ---  A4 (SDA), 2.2k or 4.7k pull-up to VCC
   A5 (SCL) ---  A5 (SCL), 2.2k or 4.7k pull-up to VCC
   GND      ---  GND 

• Wire Library, Explored - An indepth reference to the Arduino Wire library.
  http://playground.arduino.cc/Main/WireLibraryDetailedReference
• Arduino > Communication Between Arduinos Using I2C
  http://jamesreubenknowles.com/arduino-i2c-1680
• I2C between Arduino's
  http://www.instructables.com/id/I2C-between-Arduinos/