Search wiring.org.co:

This example is for Wiring version 1.0 build 0100+. If you have a previous version, use the examples included with your software. If you see any errors or have comments, please let us know.

Copyright (C) 2009 Jeff Hoefs. All rights reserved. Copyright (C) 2009 Shigeru Kobayashi. All rights reserved.
This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. See file LICENSE.txt for further informations on licensing terms.

    #include <Wire.h>
    #include <Firmata.h>

    #define I2C_WRITE B00000000
    #define I2C_READ B00001000
    #define I2C_READ_CONTINUOUSLY B00010000
    #define I2C_STOP_READING B00011000
    #define I2C_READ_WRITE_MODE_MASK B00011000

    #define MAX_QUERIES 8

    unsigned long currentMillis;     // store the current value from millis()
    unsigned long previousMillis;    // for comparison with currentMillis
    unsigned int samplingInterval = 32;  // default sampling interval is 33ms
    unsigned int i2cReadDelayTime = 0;  // default delay time between i2c read request and Wire.requestFrom()
    unsigned int powerPinsEnabled = 0;  // use as boolean to prevent enablePowerPins from being called more than once

    #define MINIMUM_SAMPLING_INTERVAL 10

    #define REGISTER_NOT_SPECIFIED -1

    struct i2c_device_info {
      byte addr;
      byte reg;
      byte bytes;
    };

    i2c_device_info query[MAX_QUERIES];

    byte i2cRxData[32];
    boolean readingContinuously = false;
    byte queryIndex = 0;

    void readAndReportData(byte address, int theRegister, byte numBytes)
    {
      if (theRegister != REGISTER_NOT_SPECIFIED) {
        Wire.beginTransmission(address);
        Wire.write(theRegister);
        Wire.endTransmission();
        delayMicroseconds(i2cReadDelayTime);  // delay is necessary for some devices such as WiiNunchuck
      }
      else {
        theRegister = 0;  // fill the register with a dummy value
      }

      Wire.requestFrom(address, numBytes);

      // check to be sure correct number of bytes were returned by slave
      if (numBytes == Wire.available()) {
        i2cRxData[0] = address;
        i2cRxData[1] = theRegister;
        for (int i = 0; i < numBytes; i++) {
          i2cRxData[2 + i] = Wire.read();
        }
        // send slave address, register and received bytes
        Firmata.sendSysex(I2C_REPLY, numBytes + 2, i2cRxData);
      }
      else {
        if (numBytes > Wire.available()) {
          Firmata.sendString("I2C Read Error: Too many bytes received");
        } else {
          Firmata.sendString("I2C Read Error: Too few bytes received");
        }
      }

    }

    void sysexCallback(byte command, byte argc, byte *argv)
    {
      byte mode;
      byte slaveAddress;
      byte slaveRegister;
      byte data;
      int  delayTime;

      if (command == I2C_REQUEST) {
        mode = argv[1] & I2C_READ_WRITE_MODE_MASK;
        slaveAddress = argv[0];

        switch (mode) {
        case I2C_WRITE:
          Wire.beginTransmission(slaveAddress);
          for (byte i = 2; i < argc; i += 2) {
            data = argv[i] + (argv[i + 1] << 7);
            Wire.write(data);
          }
          Wire.endTransmission();
          delayMicroseconds(70); // TODO is this needed?
          break;
        case I2C_READ:
          if (argc == 6) {
            // a slave register is specified
            slaveRegister = argv[2] + (argv[3] << 7);
            data = argv[4] + (argv[5] << 7);  // bytes to read
            readAndReportData(slaveAddress, (int)slaveRegister, data);
          }
          else {
            // a slave register is NOT specified
            data = argv[2] + (argv[3] << 7);  // bytes to read
            readAndReportData(slaveAddress, (int)REGISTER_NOT_SPECIFIED, data);
          }
          break;
        case I2C_READ_CONTINUOUSLY:
          if ((queryIndex + 1) >= MAX_QUERIES) {
            // too many queries, just ignore
            Firmata.sendString("too many queries");
            break;
          }
          query[queryIndex].addr = slaveAddress;
          query[queryIndex].reg = argv[2] + (argv[3] << 7);
          query[queryIndex].bytes = argv[4] + (argv[5] << 7);
          readingContinuously = true;
          queryIndex++;
          break;
        case I2C_STOP_READING:
          readingContinuously = false;
          queryIndex = 0;
          break;
        default:
          break;
        }
      }
      else if (command == SAMPLING_INTERVAL) {
        samplingInterval = argv[0] + (argv[1] << 7);

        if (samplingInterval < MINIMUM_SAMPLING_INTERVAL) {
          samplingInterval = MINIMUM_SAMPLING_INTERVAL;
        }

        samplingInterval -= 1;
        Firmata.sendString("sampling interval");
      }

      else if (command == I2C_CONFIG) {
        delayTime = (argv[4] + (argv[5] << 7));                        // MSB
        delayTime = (delayTime << 8) + (argv[2] + (argv[3] << 7));     // add LSB

        if ((argv[0] + (argv[1] << 7)) > 0) {
          enablePowerPins(PORTC3, PORTC2);
        }

        if (delayTime > 0) {
          i2cReadDelayTime = delayTime;
        }

        if (argc > 6) {
          // If you extend I2C_Config, handle your data here
        }

      }
    }

    void systemResetCallback()
    {
      readingContinuously = false;
      queryIndex = 0;
    }

    /* reference: BlinkM_funcs.h by Tod E. Kurt, ThingM, http://thingm.com/ */
    // Enables Pins A2 and A3 to be used as GND and Power
    // so that I2C devices can be plugged directly
    // into Arduino header (pins A2 - A5)
    static void enablePowerPins(byte pwrpin, byte gndpin)
    {
      if (powerPinsEnabled == 0) {
        DDRC |= _BV(pwrpin) | _BV(gndpin);
        PORTC &=~ _BV(gndpin);
        PORTC |=  _BV(pwrpin);
        powerPinsEnabled = 1;
        Firmata.sendString("Power pins enabled");
        delay(100);
      }
    }

    void setup()
    {
      Firmata.setFirmwareVersion(2, 0);

      Firmata.attach(START_SYSEX, sysexCallback);
      Firmata.attach(SYSTEM_RESET, systemResetCallback);

      for (int i = 0; i < TOTAL_PINS; ++i) {
        pinMode(i, OUTPUT);
      }

      Firmata.begin(57600);
      Wire.begin();
    }

    void loop()
    {
      while (Firmata.available()) {
        Firmata.processInput();
      }

      currentMillis = millis();
      if (currentMillis - previousMillis > samplingInterval) {
        previousMillis += samplingInterval;

        for (byte i = 0; i < queryIndex; i++) {
          readAndReportData(query[i].addr, query[i].reg, query[i].bytes);
        }
      }
    }