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Measure capacitance values using the arduino control CN0552 evaluation version

Category: Hardware
Product Number: CN0552
1.I wonder if the CN0552 can be controlled with arduino
2.If it can be used, I would like you to send the corresponding program code that I can refer to.
3.Can the code of the AD7746 be used for the control of the CN0552 and how?  


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[edited by: GenevaCooper at 2:01 PM (GMT -5) on 5 Jan 2023]
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  • Hi Ikxaaa

    You can use any host board that has I2C and digitial input for the RDY signal. The host board will also need to provide VDD.

    Originally the CN0552 was design to be use together with the ADICUP3029.  This application uses he AD7746 no-OS driver and emulates the Linux IIO framework through the tinyiiod daemon library. The application communicates with the host computer via the serial backend, over a USB-UART physical connection. This facilitates rapid application development on a host computer, independent from embedded code development.

    So if you want to use an Arduino board you will have to develop your own code. You can use the provided No OS drivers: GitHub - analogdevicesinc/no-OS: Software drivers in C for systems without an operating system

    An example of NoOS drivers using also tinyiiod librarty can be found in the following repository; GitHub - analogdevicesinc/no-OS: Software drivers in C for systems without an operating system

    Regards

    Joan

  • Sorry, I'm a novice, so I have difficulty understanding your answer. I also have the following questions.

    No-OS driver What stage can it be used to write code and do I need to write it from scratch.

    I found the code for arduino and AD7746 from the Internet, and measured the 1pF capacitance with CN0552, and the measured data is shown in the figure.Is this code available for CN0552 and if not, I need to improve something?

    The code file is attached as the following.

    .ino file

    #include "AD7746.h"//在文件中包含外部的库
    #define CapDacvalue 4//constantName:宏指令名字的定义 value:宏指令的分配值  将任何提及CapDacvalue的值定义为4
    uint8_t capdacreg = 0;//uint8_t相当于一个字节,一种长度为8位的无符号整数  =unit8_t声明数字类型    = 赋值 
    /*------------------------------------------------------------*/
    #define RDY digitalRead(3)//逻辑输出。低电平表示使能引脚转换完成,新的数据可以利用。该引脚不用时应该悬空  从指定的数字引脚读取值
    AD7746 CapDevice;
    uint32_t CapValue = 0;
    /*------------------------------------------------------------*/
    
    void setup()//板子通电或复位后,该部分函数只会执行一次,通常我们会在setup()函数完成Arduino的初始化设置。配置I/O口,初始化串口等操作
    {
      capdacreg = (uint8_t)((CapDacvalue*0x7F)/17); //0x7f--127  电容值*127/17
      capdacreg = 0x80|capdacreg;//0x80是C语言中16进制的表示方法 相当于十进制中的128   |or(或)---位运算符
      pinMode(3,INPUT);//将3号引脚设为高阻抗模式???,用以读取传感器信号或开关信号
      Wire.begin();        // join i2c bus (address optional for master)初始化Wire库,并以主机或从机的身份加入I2C总线。通常只调用一次
      Serial.begin(115200);  // start serial for output设置输出串口、传输速度
      while(!CapDevice.testConnection())//!--非,用于反转其操作数的逻辑状态。如果条件为真,则逻辑运算符为假
      {
        Serial.println("AD7746 connect failed.");
        delay(1000);
        }
      Serial.println("AD7746 connect succeed.");//串口换行输出,AD7746成功连接
      CapDevice.reset();
      CapDevice.writeCapSetupRegister(0x81); //129
      CapDevice.writeExcSetupRegister(0x0B);//11
      CapDevice.writeConfigurationRegister(0x31);
      CapDevice.writeCapDacARegister((uint8_t)capdacreg);
      Serial.println("AD7746 setup ok.");
    }
    
    void loop()//一直循环运行
    {
      while(RDY);
      CapValue = CapDevice.getCapacitance();
      Serial.print("CapValue is : ");
      Serial.println(CapValue);
      delay(1000);
    }
    

    .cpp file

    // I2Cdev library collection - AD7746 I2C device class
    // Based on Analog Devices AD7746 Datasheet, Revision 0, 2005
    // 2012-04-01 by Peteris Skorovs <pskorovs@gmail.com>
    //
    // This I2C device library is using (and submitted as a part of) Jeff Rowberg's I2Cdevlib library,
    // which should (hopefully) always be available at https://github.com/jrowberg/i2cdevlib
    //
    // Changelog:
    //     2012-04-01 - initial release
    
    /* ============================================
    I2Cdev device library code is placed under the MIT license
    Copyright (c) 2012 Peteris Skorovs
    
    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:
    
    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.
    
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
    ===============================================
    */
    
    #include "AD7746.h"
    
    /** Default constructor, uses default I2C address.
     * @see AD7746_DEFAULT_ADDRESS
     */
    AD7746::AD7746() {
        devAddr = AD7746_DEFAULT_ADDRESS;
    }
    
    /** Specific address constructor.
     * @param address I2C address
     * @see AD7746_DEFAULT_ADDRESS
     * @see AD7746_ADDRESS
     */
    AD7746::AD7746(uint8_t address) {
        devAddr = address;
    }
    
    /** Power on and prepare for general usage.
     */
    void AD7746::initialize() {
        reset();
    }
    
    /** Verify the I2C connection.
     * Make sure the device is connected and responds as expected.
     * @return True if connection is valid, false otherwise
     */
    bool AD7746::testConnection() {
        if (I2Cdev::readByte(devAddr, AD7746_RA_STATUS, buffer)) {
            return true;
        }
        return false;
    }
    
    void AD7746::reset() {   
        
    #ifdef I2CDEV_SERIAL_DEBUG
        Serial.print("I2C (0x");
        Serial.print(devAddr, HEX);
        Serial.print(") resetting");
        Serial.print("...");
    #endif    
    
    #if ((I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO < 100) || I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE)
        Wire.beginTransmission(devAddr);
        Wire.send((uint8_t) AD7746_RESET); // send reset
    #elif (I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO >= 100)
        Wire.beginTransmission(devAddr);
        Wire.write((uint8_t) AD7746_RESET); // send reset
    #endif
    #if ((I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO < 100) || I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE)
        Wire.endTransmission();
    #elif (I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO >= 100)
        Wire.endTransmission();
    #endif
        
    #ifdef I2CDEV_SERIAL_DEBUG
        Serial.println(". Done.");
    #endif
        
    delay(1); //wait a tad for reboot
    }
    
    
    uint32_t AD7746::getCapacitance() {
        uint32_t capacitance;
        I2Cdev::readBytes(devAddr, 0, 4, buffer);
        capacitance = ((uint32_t)buffer[1] << 16) | ((uint32_t)buffer[2] << 8) | (uint32_t)buffer[3];
        
        return capacitance;
    }
    
    
    void AD7746::writeCapSetupRegister(uint8_t data) {
        I2Cdev::writeByte(devAddr, AD7746_RA_CAP_SETUP, data);
    }
    
    void AD7746::writeVtSetupRegister(uint8_t data) {
        I2Cdev::writeByte(devAddr, AD7746_RA_VT_SETUP, data);
    }
    
    
    void AD7746::writeExcSetupRegister(uint8_t data) {
        I2Cdev::writeByte(devAddr, AD7746_RA_EXC_SETUP, data);
    }
    
    
    void AD7746::writeConfigurationRegister(uint8_t data) {
        I2Cdev::writeByte(devAddr, AD7746_RA_CONFIGURATION, data);
    }
    
    
    void AD7746::writeCapDacARegister(uint8_t data) {
        I2Cdev::writeByte(devAddr, AD7746_RA_CAP_DAC_A, data);
    }
    
    void AD7746::writeCapDacBRegister(uint8_t data) {
        I2Cdev::writeByte(devAddr, AD7746_RA_CAP_DAC_B, data);
    }
    

    .h file

    // I2Cdev library collection - AD7746 I2C device class header file
    // Based on Analog Devices AD7746 Datasheet, Revision 0, 2005
    // 2012-04-01 by Peteris Skorovs <pskorovs@gmail.com>
    //
    // This I2C device library is using (and submitted as a part of) Jeff Rowberg's I2Cdevlib library,
    // which should (hopefully) always be available at https://github.com/jrowberg/i2cdevlib
    //
    // Changelog:
    //     2012-04-01 - initial release
    
    /* ============================================
    I2Cdev device library code is placed under the MIT license
    Copyright (c) 2012 Peteris Skorovs
    
    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:
    
    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.
    
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
    ===============================================
    */
    
    #ifndef _AD7746_H_
    #define _AD7746_H_
    
    #include "I2Cdev.h"
    
    
    #define AD7746_ADDRESS           0x48
    #define AD7746_DEFAULT_ADDRESS   AD7746_ADDRESS           
    
    
    #define AD7746_RA_STATUS                 0x00 // Status
    #define AD7746_RA_CAP_DATA_H             0x01 // Cap data
    #define AD7746_RA_CAP_DATA_M             0x02 // Cap data
    #define AD7746_RA_CAP_DATA_L             0x03 // Cap data
    #define AD7746_RA_VT_DATA_H              0x04 // VT data
    #define AD7746_RA_VT_DATA_M              0x05 // VT data
    #define AD7746_RA_VT_DATA_L              0x06 // VT data
    #define AD7746_RA_CAP_SETUP              0x07 // Cap Setup
    #define AD7746_RA_VT_SETUP               0x08 // VT Setup
    #define AD7746_RA_EXC_SETUP              0x09 // Exc Setup
    #define AD7746_RA_CONFIGURATION          0x0A // Configuration
    #define AD7746_RA_CAP_DAC_A              0x0B // Cap DAC A
    #define AD7746_RA_CAP_DAC_B              0x0C // Cap DAC B
    #define AD7746_RA_CAP_OFF_H              0x0D 
    #define AD7746_RA_CAP_OFF_L              0x0E 
    #define AD7746_RA_CAP_GAIN_H             0x0F
    #define AD7746_RA_CAP_GAIN_L             0x10
    #define AD7746_RA_VOLT_GAIN_H            0x11
    #define AD7746_RA_VOLT_GAIN_L            0x12
    
    #define AD7746_RESET                     0xBF
    
    // Status
    #define AD7746_EXCERR_BIT                3
    #define AD7746_RDY_BIT		               2
    #define AD7746_RDYVT_BIT                 1
    #define AD7746_RDYCAP_BIT                0
    
    // Cap Setup
    #define AD7746_CAPEN_BIT                 7
    #define AD7746_CIN2_BIT                  6
    #define AD7746_CAPDIFF_BIT               5
    #define AD7746_CACHOP_BIT                0
    
    #define AD7746_CAPEN                     (1 << AD7746_CAPEN_BIT)
    #define AD7746_CIN2                      (1 << AD7746_CIN2_BIT)
    
    // VT Setup
    #define AD7746_VTEN_BIT                  7
    #define AD7746_VTMD_BIT_1                6
    #define AD7746_VTMD_BIT_0                5
    #define AD7746_EXTREF_BIT                4
    #define AD7746_VTSHORT_BIT               1
    #define AD7746_VTCHOP_BIT	               0
    
    #define AD7746_VTEN                      (1 << AD7746_VTEN_BIT)
    
    #define AD7746_VTMD_INT_TEMP             0
    #define AD7746_VTMD_EXT_TEMP             (1 << AD7746_VTMD_BIT_0)
    #define AD7746_VTMD_VDD_MON              (1 << AD7746_VTMD_BIT_1)
    #define AD7746_VTMD_VIN                  (1 << AD7746_VTMD_BIT_1) | (1 << AD7746_VTMD_BIT_0)
    
    // Exc Setup
    #define AD7746_CLKCTRL_BIT		         7 
    #define AD7746_EXCON_BIT		         6                                            
    #define AD7746_EXCB_BIT		             5
    #define AD7746_INV_EXCB_BIT		         4
    #define AD7746_EXCA_BIT		             3
    #define AD7746_INV_EXCA_BIT		         2
    #define AD7746_EXCLVL_BIT_1              1
    #define AD7746_EXCLVL_BIT_0              0
    
    #define AD7746_EXCA                      (1 << AD7746_EXCA_BIT)
    #define AD7746_EXCB                      (1 << AD7746_EXCB_BIT)
    #define AD7746_EXCON                     (1 << AD7746_EXCON_BIT)
    
    #define AD7746_EXCLVL_VDD_X_1_8          0
    #define AD7746_EXCLVL_VDD_X_1_4          (1 << AD7746_EXCLVL_BIT_0)
    #define AD7746_EXCLVL_VDD_X_3_8          (1 << AD7746_EXCLVL_BIT_1)
    #define AD7746_EXCLVL_VDD_X_1_2          (1 << AD7746_EXCLVL_BIT_1) | (1 << AD7746_EXCLVL_BIT_0)
    
    // Configuration
    #define AD7746_VTF_BIT_1                 7
    #define AD7746_VTF_BIT_0                 6
    #define AD7746_CAPF_BIT_2                5
    #define AD7746_CAPF_BIT_1                4
    #define AD7746_CAPF_BIT_0                3
    #define AD7746_MD_BIT_2                  2
    #define AD7746_MD_BIT_1                  1
    #define AD7746_MD_BIT_0                  0
    
    #define AD7746_VTF_20P1                  0
    #define AD7746_VTF_32P1                  (1 << AD7746_VTF_BIT_0)
    #define AD7746_VTF_62P1                  (1 << AD7746_VTF_BIT_1)
    #define AD7746_VTF_122P1                 (1 << AD7746_VTF_BIT_1) | (1 << AD7746_VTF_BIT_0)
    
    #define AD7746_CAPF_11P0                 0
    #define AD7746_CAPF_11P9                 (1 << AD7746_CAPF_BIT_0)
    #define AD7746_CAPF_20P0                 (1 << AD7746_CAPF_BIT_1)
    #define AD7746_CAPF_38P0                 (1 << AD7746_CAPF_BIT_1) | (1 << AD7746_CAPF_BIT_0)
    #define AD7746_CAPF_62P0                 (1 << AD7746_CAPF_BIT_2)
    #define AD7746_CAPF_77P0                 (1 << AD7746_CAPF_BIT_2) | (1 << AD7746_CAPF_BIT_0)
    #define AD7746_CAPF_92P0                 (1 << AD7746_CAPF_BIT_2) | (1 << AD7746_CAPF_BIT_1)
    #define AD7746_CAPF_109P6                (1 << AD7746_CAPF_BIT_2) | (1 << AD7746_CAPF_BIT_1) | (1 << AD7746_CAPF_BIT_0)
    
    #define AD7746_MD_IDLE                   0
    #define AD7746_MD_CONTINUOUS_CONVERSION  (1 << AD7746_MD_BIT_0)
    #define AD7746_MD_SINGLE_CONVERSION      (1 << AD7746_MD_BIT_1)
    #define AD7746_MD_POWER_DOWN             (1 << AD7746_MD_BIT_1) | (1 << AD7746_MDF_BIT_0)
    #define AD7746_MD_OFFSET_CALIBRATION     (1 << AD7746_MD_BIT_2) | (1 << AD7746_MD_BIT_0)
    #define AD7746_MD_GAIN_CALIBRATION       (1 << AD7746_MD_BIT_2) | (1 << AD7746_MD_BIT_1)
    
    // Cap DAC A
    #define AD7746_DACAEN_BIT                7
    
    #define AD7746_DACAEN                    (1 << AD7746_DACAEN_BIT)
    
    // Cap DAC B
    #define AD7746_DACBEN_BIT                7
    
    #define AD7746_DACBEN                    (1 << AD7746_DACBEN_BIT)
    
    
    #define AD7746_DAC_COEFFICIENT           0.13385826771654F // 17pF/127
    
    
    
    class AD7746 {
        public:
            AD7746();
            AD7746(uint8_t address);
    
            void initialize();
            bool testConnection();
            void reset(); 
    
            uint32_t getCapacitance();
        
            void writeCapSetupRegister(uint8_t data);
            void writeVtSetupRegister(uint8_t data);
            void writeExcSetupRegister(uint8_t data);
            void writeConfigurationRegister(uint8_t data);
            void writeCapDacARegister(uint8_t data);
            void writeCapDacBRegister(uint8_t data);
            
    
        private:
            uint8_t devAddr;
            uint8_t buffer[19];
    };
    
    #endif /* _AD7746_H_ */
    

    i2c.cpp 

    // I2Cdev library collection - Main I2C device class
    // Abstracts bit and byte I2C R/W functions into a convenient class
    // 6/9/2012 by Jeff Rowberg <jeff@rowberg.net>
    //
    // Changelog:
    //     2012-06-09 - fix major issue with reading > 32 bytes at a time with Arduino Wire
    //                - add compiler warnings when using outdated or IDE or limited I2Cdev implementation
    //     2011-11-01 - fix write*Bits mask calculation (thanks sasquatch @ Arduino forums)
    //     2011-10-03 - added automatic Arduino version detection for ease of use
    //     2011-10-02 - added Gene Knight's NBWire TwoWire class implementation with small modifications
    //     2011-08-31 - added support for Arduino 1.0 Wire library (methods are different from 0.x)
    //     2011-08-03 - added optional timeout parameter to read* methods to easily change from default
    //     2011-08-02 - added support for 16-bit registers
    //                - fixed incorrect Doxygen comments on some methods
    //                - added timeout value for read operations (thanks mem @ Arduino forums)
    //     2011-07-30 - changed read/write function structures to return success or byte counts
    //                - made all methods static for multi-device memory savings
    //     2011-07-28 - initial release
    
    /* ============================================
    I2Cdev device library code is placed under the MIT license
    Copyright (c) 2012 Jeff Rowberg
    
    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:
    
    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.
    
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
    ===============================================
    */
    
    #include "I2Cdev.h"
    
    #if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
    
        #ifdef I2CDEV_IMPLEMENTATION_WARNINGS
            #if ARDUINO < 100
                #warning Using outdated Arduino IDE with Wire library is functionally limiting.
                #warning Arduino IDE v1.0.1+ with I2Cdev Fastwire implementation is recommended.
                #warning This I2Cdev implementation does not support:
                #warning - Repeated starts conditions
                #warning - Timeout detection (some Wire requests block forever)
            #elif ARDUINO == 100
                #warning Using outdated Arduino IDE with Wire library is functionally limiting.
                #warning Arduino IDE v1.0.1+ with I2Cdev Fastwire implementation is recommended.
                #warning This I2Cdev implementation does not support:
                #warning - Repeated starts conditions
                #warning - Timeout detection (some Wire requests block forever)
            #elif ARDUINO > 100
                /*
                #warning Using current Arduino IDE with Wire library is functionally limiting.
                #warning Arduino IDE v1.0.1+ with I2CDEV_BUILTIN_FASTWIRE implementation is recommended.
                #warning This I2Cdev implementation does not support:
                #warning - Timeout detection (some Wire requests block forever)
                */
            #endif
        #endif
    
    #elif I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE
    
        #error The I2CDEV_BUILTIN_FASTWIRE implementation is known to be broken right now. Patience, Iago!
    
    #elif I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE
    
        #ifdef I2CDEV_IMPLEMENTATION_WARNINGS
            #warning Using I2CDEV_BUILTIN_NBWIRE implementation may adversely affect interrupt detection.
            #warning This I2Cdev implementation does not support:
            #warning - Repeated starts conditions
        #endif
    
        // NBWire implementation based heavily on code by Gene Knight <Gene@Telobot.com>
        // Originally posted on the Arduino forum at http://arduino.cc/forum/index.php/topic,70705.0.html
        // Originally offered to the i2cdevlib project at http://arduino.cc/forum/index.php/topic,68210.30.html
        TwoWire Wire;
    
    #endif
    
    /** Default constructor.
     */
    I2Cdev::I2Cdev() {
    }
    
    /** Read a single bit from an 8-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register regAddr to read from
     * @param bitNum Bit position to read (0-7)
     * @param data Container for single bit value
     * @param timeout Optional read timeout in milliseconds (0 to disable, leave off to use default class value in I2Cdev::readTimeout)
     * @return Status of read operation (true = success)
     */
    int8_t I2Cdev::readBit(uint8_t devAddr, uint8_t regAddr, uint8_t bitNum, uint8_t *data, uint16_t timeout) {
        uint8_t b;
        uint8_t count = readByte(devAddr, regAddr, &b, timeout);
        *data = b & (1 << bitNum);
        return count;
    }
    
    /** Read a single bit from a 16-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register regAddr to read from
     * @param bitNum Bit position to read (0-15)
     * @param data Container for single bit value
     * @param timeout Optional read timeout in milliseconds (0 to disable, leave off to use default class value in I2Cdev::readTimeout)
     * @return Status of read operation (true = success)
     */
    int8_t I2Cdev::readBitW(uint8_t devAddr, uint8_t regAddr, uint8_t bitNum, uint16_t *data, uint16_t timeout) {
        uint16_t b;
        uint8_t count = readWord(devAddr, regAddr, &b, timeout);
        *data = b & (1 << bitNum);
        return count;
    }
    
    /** Read multiple bits from an 8-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register regAddr to read from
     * @param bitStart First bit position to read (0-7)
     * @param length Number of bits to read (not more than 8)
     * @param data Container for right-aligned value (i.e. '101' read from any bitStart position will equal 0x05)
     * @param timeout Optional read timeout in milliseconds (0 to disable, leave off to use default class value in I2Cdev::readTimeout)
     * @return Status of read operation (true = success)
     */
    int8_t I2Cdev::readBits(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint8_t *data, uint16_t timeout) {
        // 01101001 read byte
        // 76543210 bit numbers
        //    xxx   args: bitStart=4, length=3
        //    010   masked
        //   -> 010 shifted
        uint8_t count, b;
        if ((count = readByte(devAddr, regAddr, &b, timeout)) != 0) {
            uint8_t mask = ((1 << length) - 1) << (bitStart - length + 1);
            b &= mask;
            b >>= (bitStart - length + 1);
            *data = b;
        }
        return count;
    }
    
    /** Read multiple bits from a 16-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register regAddr to read from
     * @param bitStart First bit position to read (0-15)
     * @param length Number of bits to read (not more than 16)
     * @param data Container for right-aligned value (i.e. '101' read from any bitStart position will equal 0x05)
     * @param timeout Optional read timeout in milliseconds (0 to disable, leave off to use default class value in I2Cdev::readTimeout)
     * @return Status of read operation (1 = success, 0 = failure, -1 = timeout)
     */
    int8_t I2Cdev::readBitsW(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint16_t *data, uint16_t timeout) {
        // 1101011001101001 read byte
        // fedcba9876543210 bit numbers
        //    xxx           args: bitStart=12, length=3
        //    010           masked
        //           -> 010 shifted
        uint8_t count;
        uint16_t w;
        if ((count = readWord(devAddr, regAddr, &w, timeout)) != 0) {
            uint16_t mask = ((1 << length) - 1) << (bitStart - length + 1);
            w &= mask;
            w >>= (bitStart - length + 1);
            *data = w;
        }
        return count;
    }
    
    /** Read single byte from an 8-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register regAddr to read from
     * @param data Container for byte value read from device
     * @param timeout Optional read timeout in milliseconds (0 to disable, leave off to use default class value in I2Cdev::readTimeout)
     * @return Status of read operation (true = success)
     */
    int8_t I2Cdev::readByte(uint8_t devAddr, uint8_t regAddr, uint8_t *data, uint16_t timeout) {
        return readBytes(devAddr, regAddr, 1, data, timeout);
    }
    
    /** Read single word from a 16-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register regAddr to read from
     * @param data Container for word value read from device
     * @param timeout Optional read timeout in milliseconds (0 to disable, leave off to use default class value in I2Cdev::readTimeout)
     * @return Status of read operation (true = success)
     */
    int8_t I2Cdev::readWord(uint8_t devAddr, uint8_t regAddr, uint16_t *data, uint16_t timeout) {
        return readWords(devAddr, regAddr, 1, data, timeout);
    }
    
    /** Read multiple bytes from an 8-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr First register regAddr to read from
     * @param length Number of bytes to read
     * @param data Buffer to store read data in
     * @param timeout Optional read timeout in milliseconds (0 to disable, leave off to use default class value in I2Cdev::readTimeout)
     * @return Number of bytes read (-1 indicates failure)
     */
    int8_t I2Cdev::readBytes(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint8_t *data, uint16_t timeout) {
        #ifdef I2CDEV_SERIAL_DEBUG
            Serial.print("I2C (0x");
            Serial.print(devAddr, HEX);
            Serial.print(") reading ");
            Serial.print(length, DEC);
            Serial.print(" bytes from 0x");
            Serial.print(regAddr, HEX);
            Serial.print("...");
        #endif
    
        int8_t count = 0;
        uint32_t t1 = millis();
    
        #if (I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE)
    
            #if (ARDUINO < 100)
                // Arduino v00xx (before v1.0), Wire library
    
                // I2C/TWI subsystem uses internal buffer that breaks with large data requests
                // so if user requests more than BUFFER_LENGTH bytes, we have to do it in
                // smaller chunks instead of all at once
                for (uint8_t k = 0; k < length; k += min(length, BUFFER_LENGTH)) {
                    Wire.beginTransmission(devAddr);
                    Wire.send(regAddr);
                    Wire.endTransmission();
                    Wire.beginTransmission(devAddr);
                    Wire.requestFrom(devAddr, (uint8_t)min(length - k, BUFFER_LENGTH));
    
                    for (; Wire.available() && (timeout == 0 || millis() - t1 < timeout); count++) {
                        data[count] = Wire.receive();
                        #ifdef I2CDEV_SERIAL_DEBUG
                            Serial.print(data[count], HEX);
                            if (count + 1 < length) Serial.print(" ");
                        #endif
                    }
    
                    Wire.endTransmission();
                }
            #elif (ARDUINO == 100)
                // Arduino v1.0.0, Wire library
                // Adds standardized write() and read() stream methods instead of send() and receive()
    
                // I2C/TWI subsystem uses internal buffer that breaks with large data requests
                // so if user requests more than BUFFER_LENGTH bytes, we have to do it in
                // smaller chunks instead of all at once
                for (uint8_t k = 0; k < length; k += min(length, BUFFER_LENGTH)) {
                    Wire.beginTransmission(devAddr);
                    Wire.write(regAddr);
                    Wire.endTransmission();
                    Wire.beginTransmission(devAddr);
                    Wire.requestFrom(devAddr, (uint8_t)min(length - k, BUFFER_LENGTH));
            
                    for (; Wire.available() && (timeout == 0 || millis() - t1 < timeout); count++) {
                        data[count] = Wire.read();
                        #ifdef I2CDEV_SERIAL_DEBUG
                            Serial.print(data[count], HEX);
                            if (count + 1 < length) Serial.print(" ");
                        #endif
                    }
            
                    Wire.endTransmission();
                }
            #elif (ARDUINO > 100)
                // Arduino v1.0.1+, Wire library
                // Adds official support for repeated start condition, yay!
    
                // I2C/TWI subsystem uses internal buffer that breaks with large data requests
                // so if user requests more than BUFFER_LENGTH bytes, we have to do it in
                // smaller chunks instead of all at once
                for (uint8_t k = 0; k < length; k += min(length, BUFFER_LENGTH)) {
                    Wire.beginTransmission(devAddr);
                    Wire.write(regAddr);
                    Wire.endTransmission();
                    Wire.beginTransmission(devAddr);
                    Wire.requestFrom(devAddr, (uint8_t)min(length - k, BUFFER_LENGTH));
            
                    for (; Wire.available() && (timeout == 0 || millis() - t1 < timeout); count++) {
                        data[count] = Wire.read();
                        #ifdef I2CDEV_SERIAL_DEBUG
                            Serial.print(data[count], HEX);
                            if (count + 1 < length) Serial.print(" ");
                        #endif
                    }
            
                    Wire.endTransmission();
                }
            #endif
    
        #elif (I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE)
            // Fastwire library (STILL UNDER DEVELOPMENT, NON-FUNCTIONAL!)
    
            // no loop required for fastwire
            uint8_t status = Fastwire::readBuf(devAddr, regAddr, data, length);
            if (status == 0) {
                count = length; // success
            } else {
                count = -1; // error
            }
    
        #endif
    
        // check for timeout
        if (timeout > 0 && millis() - t1 >= timeout && count < length) count = -1; // timeout
    
        #ifdef I2CDEV_SERIAL_DEBUG
            Serial.print(". Done (");
            Serial.print(count, DEC);
            Serial.println(" read).");
        #endif
    
        return count;
    }
    
    /** Read multiple words from a 16-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr First register regAddr to read from
     * @param length Number of words to read
     * @param data Buffer to store read data in
     * @param timeout Optional read timeout in milliseconds (0 to disable, leave off to use default class value in I2Cdev::readTimeout)
     * @return Number of words read (0 indicates failure)
     */
    int8_t I2Cdev::readWords(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint16_t *data, uint16_t timeout) {
        #ifdef I2CDEV_SERIAL_DEBUG
            Serial.print("I2C (0x");
            Serial.print(devAddr, HEX);
            Serial.print(") reading ");
            Serial.print(length, DEC);
            Serial.print(" words from 0x");
            Serial.print(regAddr, HEX);
            Serial.print("...");
        #endif
    
        int8_t count = 0;
        uint32_t t1 = millis();
    
        #if (I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE)
    
            #if (ARDUINO < 100)
                // Arduino v00xx (before v1.0), Wire library
    
                // I2C/TWI subsystem uses internal buffer that breaks with large data requests
                // so if user requests more than BUFFER_LENGTH bytes, we have to do it in
                // smaller chunks instead of all at once
                for (uint8_t k = 0; k < length * 2; k += min(length * 2, BUFFER_LENGTH)) {
                    Wire.beginTransmission(devAddr);
                    Wire.send(regAddr);
                    Wire.endTransmission();
                    Wire.beginTransmission(devAddr);
                    Wire.requestFrom(devAddr, (uint8_t)(length * 2)); // length=words, this wants bytes
        
                    bool msb = true; // starts with MSB, then LSB
                    for (; Wire.available() && count < length && (timeout == 0 || millis() - t1 < timeout);) {
                        if (msb) {
                            // first byte is bits 15-8 (MSb=15)
                            data[count] = Wire.receive() << 8;
                        } else {
                            // second byte is bits 7-0 (LSb=0)
                            data[count] |= Wire.receive();
                            #ifdef I2CDEV_SERIAL_DEBUG
                                Serial.print(data[count], HEX);
                                if (count + 1 < length) Serial.print(" ");
                            #endif
                            count++;
                        }
                        msb = !msb;
                    }
    
                    Wire.endTransmission();
                }
            #elif (ARDUINO == 100)
                // Arduino v1.0.0, Wire library
                // Adds standardized write() and read() stream methods instead of send() and receive()
        
                // I2C/TWI subsystem uses internal buffer that breaks with large data requests
                // so if user requests more than BUFFER_LENGTH bytes, we have to do it in
                // smaller chunks instead of all at once
                for (uint8_t k = 0; k < length * 2; k += min(length * 2, BUFFER_LENGTH)) {
                    Wire.beginTransmission(devAddr);
                    Wire.write(regAddr);
                    Wire.endTransmission();
                    Wire.beginTransmission(devAddr);
                    Wire.requestFrom(devAddr, (uint8_t)(length * 2)); // length=words, this wants bytes
        
                    bool msb = true; // starts with MSB, then LSB
                    for (; Wire.available() && count < length && (timeout == 0 || millis() - t1 < timeout);) {
                        if (msb) {
                            // first byte is bits 15-8 (MSb=15)
                            data[count] = Wire.read() << 8;
                        } else {
                            // second byte is bits 7-0 (LSb=0)
                            data[count] |= Wire.read();
                            #ifdef I2CDEV_SERIAL_DEBUG
                                Serial.print(data[count], HEX);
                                if (count + 1 < length) Serial.print(" ");
                            #endif
                            count++;
                        }
                        msb = !msb;
                    }
            
                    Wire.endTransmission();
                }
            #elif (ARDUINO > 100)
                // Arduino v1.0.1+, Wire library
                // Adds official support for repeated start condition, yay!
    
                // I2C/TWI subsystem uses internal buffer that breaks with large data requests
                // so if user requests more than BUFFER_LENGTH bytes, we have to do it in
                // smaller chunks instead of all at once
                for (uint8_t k = 0; k < length * 2; k += min(length * 2, BUFFER_LENGTH)) {
                    Wire.beginTransmission(devAddr);
                    Wire.write(regAddr);
                    Wire.endTransmission();
                    Wire.beginTransmission(devAddr);
                    Wire.requestFrom(devAddr, (uint8_t)(length * 2)); // length=words, this wants bytes
            
                    bool msb = true; // starts with MSB, then LSB
                    for (; Wire.available() && count < length && (timeout == 0 || millis() - t1 < timeout);) {
                        if (msb) {
                            // first byte is bits 15-8 (MSb=15)
                            data[count] = Wire.read() << 8;
                        } else {
                            // second byte is bits 7-0 (LSb=0)
                            data[count] |= Wire.read();
                            #ifdef I2CDEV_SERIAL_DEBUG
                                Serial.print(data[count], HEX);
                                if (count + 1 < length) Serial.print(" ");
                            #endif
                            count++;
                        }
                        msb = !msb;
                    }
            
                    Wire.endTransmission();
                }
            #endif
    
        #elif (I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE)
            // Fastwire library (STILL UNDER DEVELOPMENT, NON-FUNCTIONAL!)
    
            // no loop required for fastwire
            uint16_t intermediate[(uint8_t)length];
            uint8_t status = Fastwire::readBuf(devAddr, regAddr, (uint8_t *)intermediate, (uint8_t)(length * 2));
            if (status == 0) {
                count = length; // success
                for (uint8_t i = 0; i < length; i++) {
                    data[i] = (intermediate[2*i] << 8) | intermediate[2*i + 1];
                }
            } else {
                count = -1; // error
            }
    
        #endif
    
        if (timeout > 0 && millis() - t1 >= timeout && count < length) count = -1; // timeout
    
        #ifdef I2CDEV_SERIAL_DEBUG
            Serial.print(". Done (");
            Serial.print(count, DEC);
            Serial.println(" read).");
        #endif
        
        return count;
    }
    
    /** write a single bit in an 8-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register regAddr to write to
     * @param bitNum Bit position to write (0-7)
     * @param value New bit value to write
     * @return Status of operation (true = success)
     */
    bool I2Cdev::writeBit(uint8_t devAddr, uint8_t regAddr, uint8_t bitNum, uint8_t data) {
        uint8_t b;
        readByte(devAddr, regAddr, &b);
        b = (data != 0) ? (b | (1 << bitNum)) : (b & ~(1 << bitNum));
        return writeByte(devAddr, regAddr, b);
    }
    
    /** write a single bit in a 16-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register regAddr to write to
     * @param bitNum Bit position to write (0-15)
     * @param value New bit value to write
     * @return Status of operation (true = success)
     */
    bool I2Cdev::writeBitW(uint8_t devAddr, uint8_t regAddr, uint8_t bitNum, uint16_t data) {
        uint16_t w;
        readWord(devAddr, regAddr, &w);
        w = (data != 0) ? (w | (1 << bitNum)) : (w & ~(1 << bitNum));
        return writeWord(devAddr, regAddr, w);
    }
    
    /** Write multiple bits in an 8-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register regAddr to write to
     * @param bitStart First bit position to write (0-7)
     * @param length Number of bits to write (not more than 8)
     * @param data Right-aligned value to write
     * @return Status of operation (true = success)
     */
    bool I2Cdev::writeBits(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint8_t data) {
        //      010 value to write
        // 76543210 bit numbers
        //    xxx   args: bitStart=4, length=3
        // 00011100 mask byte
        // 10101111 original value (sample)
        // 10100011 original & ~mask
        // 10101011 masked | value
        uint8_t b;
        if (readByte(devAddr, regAddr, &b) != 0) {
            uint8_t mask = ((1 << length) - 1) << (bitStart - length + 1);
            data <<= (bitStart - length + 1); // shift data into correct position
            data &= mask; // zero all non-important bits in data
            b &= ~(mask); // zero all important bits in existing byte
            b |= data; // combine data with existing byte
            return writeByte(devAddr, regAddr, b);
        } else {
            return false;
        }
    }
    
    /** Write multiple bits in a 16-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register regAddr to write to
     * @param bitStart First bit position to write (0-15)
     * @param length Number of bits to write (not more than 16)
     * @param data Right-aligned value to write
     * @return Status of operation (true = success)
     */
    bool I2Cdev::writeBitsW(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint16_t data) {
        //              010 value to write
        // fedcba9876543210 bit numbers
        //    xxx           args: bitStart=12, length=3
        // 0001110000000000 mask byte
        // 1010111110010110 original value (sample)
        // 1010001110010110 original & ~mask
        // 1010101110010110 masked | value
        uint16_t w;
        if (readWord(devAddr, regAddr, &w) != 0) {
            uint8_t mask = ((1 << length) - 1) << (bitStart - length + 1);
            data <<= (bitStart - length + 1); // shift data into correct position
            data &= mask; // zero all non-important bits in data
            w &= ~(mask); // zero all important bits in existing word
            w |= data; // combine data with existing word
            return writeWord(devAddr, regAddr, w);
        } else {
            return false;
        }
    }
    
    /** Write single byte to an 8-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register address to write to
     * @param data New byte value to write
     * @return Status of operation (true = success)
     */
    bool I2Cdev::writeByte(uint8_t devAddr, uint8_t regAddr, uint8_t data) {
        return writeBytes(devAddr, regAddr, 1, &data);
    }
    
    /** Write single word to a 16-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr Register address to write to
     * @param data New word value to write
     * @return Status of operation (true = success)
     */
    bool I2Cdev::writeWord(uint8_t devAddr, uint8_t regAddr, uint16_t data) {
        return writeWords(devAddr, regAddr, 1, &data);
    }
    
    /** Write multiple bytes to an 8-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr First register address to write to
     * @param length Number of bytes to write
     * @param data Buffer to copy new data from
     * @return Status of operation (true = success)
     */
    bool I2Cdev::writeBytes(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint8_t* data) {
        #ifdef I2CDEV_SERIAL_DEBUG
            Serial.print("I2C (0x");
            Serial.print(devAddr, HEX);
            Serial.print(") writing ");
            Serial.print(length, DEC);
            Serial.print(" bytes to 0x");
            Serial.print(regAddr, HEX);
            Serial.print("...");
        #endif
        uint8_t status = 0;
        #if ((I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO < 100) || I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE)
            Wire.beginTransmission(devAddr);
            Wire.send((uint8_t) regAddr); // send address
        #elif (I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO >= 100)
            Wire.beginTransmission(devAddr);
            Wire.write((uint8_t) regAddr); // send address
        #endif
        for (uint8_t i = 0; i < length; i++) {
            #if ((I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO < 100) || I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE)
                Wire.send((uint8_t) data[i]);
            #elif (I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO >= 100)
                Wire.write((uint8_t) data[i]);
            #elif (I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE)
                status = Fastwire::write(devAddr, regAddr, data[i]);
                Serial.println(status);
            #endif
            #ifdef I2CDEV_SERIAL_DEBUG
                Serial.print(data[i], HEX);
                if (i + 1 < length) Serial.print(" ");
            #endif
        }
        #if ((I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO < 100) || I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE)
            Wire.endTransmission();
        #elif (I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO >= 100)
            status = Wire.endTransmission();
        #endif
        #ifdef I2CDEV_SERIAL_DEBUG
            Serial.println(". Done.");
        #endif
        return status == 0;
    }
    
    /** Write multiple words to a 16-bit device register.
     * @param devAddr I2C slave device address
     * @param regAddr First register address to write to
     * @param length Number of words to write
     * @param data Buffer to copy new data from
     * @return Status of operation (true = success)
     */
    bool I2Cdev::writeWords(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint16_t* data) {
        #ifdef I2CDEV_SERIAL_DEBUG
            Serial.print("I2C (0x");
            Serial.print(devAddr, HEX);
            Serial.print(") writing ");
            Serial.print(length, DEC);
            Serial.print(" words to 0x");
            Serial.print(regAddr, HEX);
            Serial.print("...");
        #endif
        uint8_t status = 0;
        #if ((I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO < 100) || I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE)
            Wire.beginTransmission(devAddr);
            Wire.send(regAddr); // send address
        #elif (I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO >= 100)
            Wire.beginTransmission(devAddr);
            Wire.write(regAddr); // send address
        #endif
        for (uint8_t i = 0; i < length * 2; i++) {
            #if ((I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO < 100) || I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE)
                Wire.send((uint8_t)(data[i++] >> 8)); // send MSB
                Wire.send((uint8_t)data[i]);          // send LSB
            #elif (I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO >= 100)
                Wire.write((uint8_t)(data[i++] >> 8)); // send MSB
                Wire.write((uint8_t)data[i]);          // send LSB
            #elif (I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE)
                status = Fastwire::write(devAddr, regAddr, (uint8_t)(data[i++] >> 8));
                status = Fastwire::write(devAddr, regAddr + 1, (uint8_t)data[i]);
            #endif
            #ifdef I2CDEV_SERIAL_DEBUG
                Serial.print(data[i], HEX);
                if (i + 1 < length) Serial.print(" ");
            #endif
        }
        #if ((I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO < 100) || I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE)
            Wire.endTransmission();
        #elif (I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE && ARDUINO >= 100)
            status = Wire.endTransmission();
        #endif
        #ifdef I2CDEV_SERIAL_DEBUG
            Serial.println(". Done.");
        #endif
        return status == 0;
    }
    
    /** Default timeout value for read operations.
     * Set this to 0 to disable timeout detection.
     */
    uint16_t I2Cdev::readTimeout = I2CDEV_DEFAULT_READ_TIMEOUT;
    
    #if I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE
        /*
        FastWire 0.2
        This is a library to help faster programs to read I2C devices.
        Copyright(C) 2011 Francesco Ferrara
        occhiobello at gmail dot com
        */
    
        boolean Fastwire::waitInt() {
            int l = 250;
            while (!(TWCR & (1 << TWINT)) && l-- > 0);
            return l > 0;
        }
    
        void Fastwire::setup(int khz, boolean pullup) {
            TWCR = 0;
            #if defined(__AVR_ATmega168__) || defined(__AVR_ATmega8__) || defined(__AVR_ATmega328P__)
                // activate internal pull-ups for twi (PORTC bits 4 & 5)
                // as per note from atmega8 manual pg167
                if (pullup) PORTC |= ((1 << 4) | (1 << 5));
                else        PORTC &= ~((1 << 4) | (1 << 5));
            #elif defined(__AVR_ATmega644P__) || defined(__AVR_ATmega644__)
                // activate internal pull-ups for twi (PORTC bits 0 & 1)
                if (pullup) PORTC |= ((1 << 0) | (1 << 1));
                else        PORTC &= ~((1 << 0) | (1 << 1));
            #else
                // activate internal pull-ups for twi (PORTD bits 0 & 1)
                // as per note from atmega128 manual pg204
                if (pullup) PORTD |= ((1 << 0) | (1 << 1));
                else        PORTD &= ~((1 << 0) | (1 << 1));
            #endif
    
            TWSR = 0; // no prescaler => prescaler = 1
            TWBR = ((16000L / khz) - 16) / 2; // change the I2C clock rate
            TWCR = 1 << TWEN; // enable twi module, no interrupt
        }
    
        byte Fastwire::write(byte device, byte address, byte value) {
            byte twst, retry;
    
            retry = 2;
            do {
                TWCR = (1 << TWINT) | (1 << TWEN) | (1 << TWSTO) | (1 << TWSTA);
                if (!waitInt()) return 1;
                twst = TWSR & 0xF8;
                if (twst != TW_START && twst != TW_REP_START) return 2;
    
                TWDR = device & 0xFE; // send device address without read bit (1)
                TWCR = (1 << TWINT) | (1 << TWEN);
                if (!waitInt()) return 3;
                twst = TWSR & 0xF8;
            } while (twst == TW_MT_SLA_NACK && retry-- > 0);
            if (twst != TW_MT_SLA_ACK) return 4;
    
            TWDR = address; // send data to the previously addressed device
            TWCR = (1 << TWINT) | (1 << TWEN);
            if (!waitInt()) return 5;
            twst = TWSR & 0xF8;
            if (twst != TW_MT_DATA_ACK) return 6;
    
            TWDR = value; // send data to the previously addressed device
            TWCR = (1 << TWINT) | (1 << TWEN);
            if (!waitInt()) return 7;
            twst = TWSR & 0xF8;
            if (twst != TW_MT_DATA_ACK) return 8;
    
            return 0;
        }
    
        byte Fastwire::readBuf(byte device, byte address, byte *data, byte num) {
            byte twst, retry;
    
            retry = 2;
            do {
                TWCR = (1 << TWINT) | (1 << TWEN) | (1 << TWSTO) | (1 << TWSTA);
                if (!waitInt()) return 16;
                twst = TWSR & 0xF8;
                if (twst != TW_START && twst != TW_REP_START) return 17;
    
                TWDR = device & 0xfe; // send device address to write
                TWCR = (1 << TWINT) | (1 << TWEN);
                if (!waitInt()) return 18;
                twst = TWSR & 0xF8;
            } while (twst == TW_MT_SLA_NACK && retry-- > 0);
            if (twst != TW_MT_SLA_ACK) return 19;
    
            TWDR = address; // send data to the previously addressed device
            TWCR = (1 << TWINT) | (1 << TWEN);
            if (!waitInt()) return 20;
            twst = TWSR & 0xF8;
            if (twst != TW_MT_DATA_ACK) return 21;
    
            /***/
    
            retry = 2;
            do {
                TWCR = (1 << TWINT) | (1 << TWEN) | (1 << TWSTO) | (1 << TWSTA);
                if (!waitInt()) return 22;
                twst = TWSR & 0xF8;
                if (twst != TW_START && twst != TW_REP_START) return 23;
    
                TWDR = device | 0x01; // send device address with the read bit (1)
                TWCR = (1 << TWINT) | (1 << TWEN);
                if (!waitInt()) return 24;
                twst = TWSR & 0xF8;
            } while (twst == TW_MR_SLA_NACK && retry-- > 0);
            if (twst != TW_MR_SLA_ACK) return 25;
    
            for(uint8_t i = 0; i < num; i++) {
                if (i == num - 1)
                   TWCR = (1 << TWINT) | (1 << TWEN);
                else
                    TWCR = (1 << TWINT) | (1 << TWEN) | (1 << TWEA);
                if (!waitInt()) return 26;
                twst = TWSR & 0xF8;
                if (twst != TW_MR_DATA_ACK && twst != TW_MR_DATA_NACK) return twst;
                data[i] = TWDR;
            }
    
            return 0;
       }
    #endif
    
    #if I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE
        // NBWire implementation based heavily on code by Gene Knight <Gene@Telobot.com>
        // Originally posted on the Arduino forum at http://arduino.cc/forum/index.php/topic,70705.0.html
        // Originally offered to the i2cdevlib project at http://arduino.cc/forum/index.php/topic,68210.30.html
    
        /*
        call this version 1.0
        
        Offhand, the only funky part that I can think of is in nbrequestFrom, where the buffer
        length and index are set *before* the data is actually read. The problem is that these
        are variables local to the TwoWire object, and by the time we actually have read the
        data, and know what the length actually is, we have no simple access to the object's 
        variables. The actual bytes read *is* given to the callback function, though.
        
        The ISR code for a slave receiver is commented out. I don't have that setup, and can't
        verify it at this time. Save it for 2.0!
        
        The handling of the read and write processes here is much like in the demo sketch code: 
        the process is broken down into sequential functions, where each registers the next as a
        callback, essentially.
        
        For example, for the Read process, twi_read00 just returns if TWI is not yet in a 
        ready state. When there's another interrupt, and the interface *is* ready, then it
        sets up the read, starts it, and registers twi_read01 as the function to call after
        the *next* interrupt. twi_read01, then, just returns if the interface is still in a
        "reading" state. When the reading is done, it copies the information to the buffer,
        cleans up, and calls the user-requested callback function with the actual number of 
        bytes read.
        
        The writing is similar.
        
        Questions, comments and problems can go to Gene@Telobot.com.
        
        Thumbs Up!
        Gene Knight
        
        */
        
        uint8_t TwoWire::rxBuffer[NBWIRE_BUFFER_LENGTH];
        uint8_t TwoWire::rxBufferIndex = 0;
        uint8_t TwoWire::rxBufferLength = 0;
        
        uint8_t TwoWire::txAddress = 0;
        uint8_t TwoWire::txBuffer[NBWIRE_BUFFER_LENGTH];
        uint8_t TwoWire::txBufferIndex = 0;
        uint8_t TwoWire::txBufferLength = 0;
        
        //uint8_t TwoWire::transmitting = 0;
        void (*TwoWire::user_onRequest)(void);
        void (*TwoWire::user_onReceive)(int);
        
        static volatile uint8_t twi_transmitting;
        static volatile uint8_t twi_state;
        static uint8_t twi_slarw;
        static volatile uint8_t twi_error;
        static uint8_t twi_masterBuffer[TWI_BUFFER_LENGTH];
        static volatile uint8_t twi_masterBufferIndex;
        static uint8_t twi_masterBufferLength;
        static uint8_t twi_rxBuffer[TWI_BUFFER_LENGTH];
        static volatile uint8_t twi_rxBufferIndex;
        //static volatile uint8_t twi_Interrupt_Continue_Command;
        static volatile uint8_t twi_Return_Value;
        static volatile uint8_t twi_Done;
        void (*twi_cbendTransmissionDone)(int);
        void (*twi_cbreadFromDone)(int);
        
        void twi_init() {
            // initialize state
            twi_state = TWI_READY;
    
            // activate internal pull-ups for twi
            // as per note from atmega8 manual pg167
            sbi(PORTC, 4);
            sbi(PORTC, 5);
    
            // initialize twi prescaler and bit rate
            cbi(TWSR, TWPS0); // TWI Status Register - Prescaler bits
            cbi(TWSR, TWPS1);
    
            /* twi bit rate formula from atmega128 manual pg 204
            SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
            note: TWBR should be 10 or higher for master mode
            It is 72 for a 16mhz Wiring board with 100kHz TWI */
    
            TWBR = ((CPU_FREQ / TWI_FREQ) - 16) / 2; // bitrate register
            // enable twi module, acks, and twi interrupt
    
            TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA);
    
            /* TWEN - TWI Enable Bit
            TWIE - TWI Interrupt Enable
            TWEA - TWI Enable Acknowledge Bit
            TWINT - TWI Interrupt Flag
            TWSTA - TWI Start Condition
            */
        }
        
        typedef struct {
            uint8_t address;
            uint8_t* data;
            uint8_t length;
            uint8_t wait;
            uint8_t i;
        } twi_Write_Vars;
    
        twi_Write_Vars *ptwv = 0;
        static void (*fNextInterruptFunction)(void) = 0;
        
        void twi_Finish(byte bRetVal) {
            if (ptwv) {
                free(ptwv);
                ptwv = 0;
            }
            twi_Done = 0xFF;
            twi_Return_Value = bRetVal;
            fNextInterruptFunction = 0;
        }
        
        uint8_t twii_WaitForDone(uint16_t timeout) {
            uint32_t endMillis = millis() + timeout;
            while (!twi_Done && (timeout == 0 || millis() < endMillis)) continue;
            return twi_Return_Value;
        }
        
        void twii_SetState(uint8_t ucState) {
            twi_state = ucState;
        }
    
        void twii_SetError(uint8_t ucError) {
            twi_error = ucError ;
        }
    
        void twii_InitBuffer(uint8_t ucPos, uint8_t ucLength) {
            twi_masterBufferIndex = 0;
            twi_masterBufferLength = ucLength;
        }
    
        void twii_CopyToBuf(uint8_t* pData, uint8_t ucLength) {
            uint8_t i;
            for (i = 0; i < ucLength; ++i) {
                twi_masterBuffer[i] = pData[i];
            }
        }
    
        void twii_CopyFromBuf(uint8_t *pData, uint8_t ucLength) {
            uint8_t i;
            for (i = 0; i < ucLength; ++i) {
                pData[i] = twi_masterBuffer[i];
            }
        }
    
        void twii_SetSlaRW(uint8_t ucSlaRW) {
            twi_slarw = ucSlaRW;
        }
    
        void twii_SetStart() {
            TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);
        }
    
        void twi_write01() {
            if (TWI_MTX == twi_state) return; // blocking test
            twi_transmitting = 0 ;
            if (twi_error == 0xFF)
                twi_Finish (0);    // success
            else if (twi_error == TW_MT_SLA_NACK)
                twi_Finish (2);    // error: address send, nack received
            else if (twi_error == TW_MT_DATA_NACK)
                twi_Finish (3);    // error: data send, nack received
            else
                twi_Finish (4);    // other twi error
            if (twi_cbendTransmissionDone) return twi_cbendTransmissionDone(twi_Return_Value);
            return;
        }
        
        
        void twi_write00() {
            if (TWI_READY != twi_state) return; // blocking test
            if (TWI_BUFFER_LENGTH < ptwv -> length) {
                twi_Finish(1); // end write with error 1
                return;
            }
            twi_Done = 0x00; // show as working
            twii_SetState(TWI_MTX); // to transmitting
            twii_SetError(0xFF); // to No Error
            twii_InitBuffer(0, ptwv -> length); // pointer and length
            twii_CopyToBuf(ptwv -> data, ptwv -> length); // get the data
            twii_SetSlaRW((ptwv -> address << 1) | TW_WRITE); // write command
            twii_SetStart(); // start the cycle
            fNextInterruptFunction = twi_write01; // next routine
            return twi_write01();
        }
        
        void twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait) {
            uint8_t i;
            ptwv = (twi_Write_Vars *)malloc(sizeof(twi_Write_Vars));
            ptwv -> address = address;
            ptwv -> data = data;
            ptwv -> length = length;
            ptwv -> wait = wait;
            fNextInterruptFunction = twi_write00;
            return twi_write00();
        }
    
        void twi_read01() {
            if (TWI_MRX == twi_state) return; // blocking test
            if (twi_masterBufferIndex < ptwv -> length) ptwv -> length = twi_masterBufferIndex;
            twii_CopyFromBuf(ptwv -> data, ptwv -> length);
            twi_Finish(ptwv -> length);
            if (twi_cbreadFromDone) return twi_cbreadFromDone(twi_Return_Value);
            return;
        }
        
        void twi_read00() {
            if (TWI_READY != twi_state) return; // blocking test
            if (TWI_BUFFER_LENGTH < ptwv -> length) twi_Finish(0); // error return
            twi_Done = 0x00; // show as working
            twii_SetState(TWI_MRX); // reading
            twii_SetError(0xFF); // reset error
            twii_InitBuffer(0, ptwv -> length - 1); // init to one less than length
            twii_SetSlaRW((ptwv -> address << 1) | TW_READ); // read command
            twii_SetStart(); // start cycle
            fNextInterruptFunction = twi_read01;
            return twi_read01();
        }
    
        void twi_readFrom(uint8_t address, uint8_t* data, uint8_t length) {
            uint8_t i;
    
            ptwv = (twi_Write_Vars *)malloc(sizeof(twi_Write_Vars));
            ptwv -> address = address;
            ptwv -> data = data;
            ptwv -> length = length;
            fNextInterruptFunction = twi_read00;
            return twi_read00();
        }
    
        void twi_reply(uint8_t ack) {
            // transmit master read ready signal, with or without ack
            if (ack){
                TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT) | _BV(TWEA);
            } else {
                TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT);
            }
        }
        
        void twi_stop(void) {
            // send stop condition
            TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTO);
        
            // wait for stop condition to be exectued on bus
            // TWINT is not set after a stop condition!
            while (TWCR & _BV(TWSTO)) {
                continue;
            }
        
            // update twi state
            twi_state = TWI_READY;
        }
    
        void twi_releaseBus(void) {
            // release bus
            TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT);
        
            // update twi state
            twi_state = TWI_READY;
        }
        
        SIGNAL(TWI_vect) {
            switch (TW_STATUS) {
                // All Master
                case TW_START:     // sent start condition
                case TW_REP_START: // sent repeated start condition
                    // copy device address and r/w bit to output register and ack
                    TWDR = twi_slarw;
                    twi_reply(1);
                    break;
        
                // Master Transmitter
                case TW_MT_SLA_ACK:  // slave receiver acked address
                case TW_MT_DATA_ACK: // slave receiver acked data
                    // if there is data to send, send it, otherwise stop
                    if (twi_masterBufferIndex < twi_masterBufferLength) {
                        // copy data to output register and ack
                        TWDR = twi_masterBuffer[twi_masterBufferIndex++];
                        twi_reply(1);
                    } else {
                        twi_stop();
                    }
                    break;
    
                case TW_MT_SLA_NACK:  // address sent, nack received
                    twi_error = TW_MT_SLA_NACK;
                    twi_stop();
                    break;
    
                case TW_MT_DATA_NACK: // data sent, nack received
                    twi_error = TW_MT_DATA_NACK;
                    twi_stop();
                    break;
    
                case TW_MT_ARB_LOST: // lost bus arbitration
                    twi_error = TW_MT_ARB_LOST;
                    twi_releaseBus();
                    break;
        
                // Master Receiver
                case TW_MR_DATA_ACK: // data received, ack sent
                    // put byte into buffer
                    twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
    
                case TW_MR_SLA_ACK:  // address sent, ack received
                    // ack if more bytes are expected, otherwise nack
                    if (twi_masterBufferIndex < twi_masterBufferLength) {
                        twi_reply(1);
                    } else {
                        twi_reply(0);
                    }
                    break;
    
                case TW_MR_DATA_NACK: // data received, nack sent
                    // put final byte into buffer
                    twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
    
                case TW_MR_SLA_NACK: // address sent, nack received
                    twi_stop();
                    break;
    
            // TW_MR_ARB_LOST handled by TW_MT_ARB_LOST case
    
            // Slave Receiver (NOT IMPLEMENTED YET)
            /*
                case TW_SR_SLA_ACK:   // addressed, returned ack
                case TW_SR_GCALL_ACK: // addressed generally, returned ack
                case TW_SR_ARB_LOST_SLA_ACK:   // lost arbitration, returned ack
                case TW_SR_ARB_LOST_GCALL_ACK: // lost arbitration, returned ack
                    // enter slave receiver mode
                    twi_state = TWI_SRX;
    
                    // indicate that rx buffer can be overwritten and ack
                    twi_rxBufferIndex = 0;
                    twi_reply(1);
                    break;
    
                case TW_SR_DATA_ACK:       // data received, returned ack
                case TW_SR_GCALL_DATA_ACK: // data received generally, returned ack
                    // if there is still room in the rx buffer
                    if (twi_rxBufferIndex < TWI_BUFFER_LENGTH) {
                        // put byte in buffer and ack
                        twi_rxBuffer[twi_rxBufferIndex++] = TWDR;
                        twi_reply(1);
                    } else {
                        // otherwise nack
                        twi_reply(0);
                    }
                    break;
    
                case TW_SR_STOP: // stop or repeated start condition received
                    // put a null char after data if there's room
                    if (twi_rxBufferIndex < TWI_BUFFER_LENGTH) {
                        twi_rxBuffer[twi_rxBufferIndex] = 0;
                    }
    
                    // sends ack and stops interface for clock stretching
                    twi_stop();
    
                    // callback to user defined callback
                    twi_onSlaveReceive(twi_rxBuffer, twi_rxBufferIndex);
    
                    // since we submit rx buffer to "wire" library, we can reset it
                    twi_rxBufferIndex = 0;
    
                    // ack future responses and leave slave receiver state
                    twi_releaseBus();
                    break;
    
                case TW_SR_DATA_NACK:       // data received, returned nack
                case TW_SR_GCALL_DATA_NACK: // data received generally, returned nack
                    // nack back at master
                    twi_reply(0);
                    break;
    
                // Slave Transmitter
                case TW_ST_SLA_ACK:          // addressed, returned ack
                case TW_ST_ARB_LOST_SLA_ACK: // arbitration lost, returned ack
                    // enter slave transmitter mode
                    twi_state = TWI_STX;
    
                    // ready the tx buffer index for iteration
                    twi_txBufferIndex = 0;
    
                    // set tx buffer length to be zero, to verify if user changes it
                    twi_txBufferLength = 0;
    
                    // request for txBuffer to be filled and length to be set
                    // note: user must call twi_transmit(bytes, length) to do this
                    twi_onSlaveTransmit();
    
                    // if they didn't change buffer & length, initialize it
                    if (0 == twi_txBufferLength) {
                        twi_txBufferLength = 1;
                        twi_txBuffer[0] = 0x00;
                    }
                    
                    // transmit first byte from buffer, fall through
    
                case TW_ST_DATA_ACK: // byte sent, ack returned
                    // copy data to output register
                    TWDR = twi_txBuffer[twi_txBufferIndex++];
    
                    // if there is more to send, ack, otherwise nack
                    if (twi_txBufferIndex < twi_txBufferLength) {
                        twi_reply(1);
                    } else {
                        twi_reply(0);
                    }
                    break;
    
                case TW_ST_DATA_NACK: // received nack, we are done
                case TW_ST_LAST_DATA: // received ack, but we are done already!
                    // ack future responses
                    twi_reply(1);
                    // leave slave receiver state
                    twi_state = TWI_READY;
                    break;
                */
    
                // all
                case TW_NO_INFO:   // no state information
                    break;
    
                case TW_BUS_ERROR: // bus error, illegal stop/start
                    twi_error = TW_BUS_ERROR;
                    twi_stop();
                    break;
            }
    
            if (fNextInterruptFunction) return fNextInterruptFunction();
        }
    
        TwoWire::TwoWire() { }
        
        void TwoWire::begin(void) {
            rxBufferIndex = 0;
            rxBufferLength = 0;
        
            txBufferIndex = 0;
            txBufferLength = 0;
    
            twi_init();
        }
        
        void TwoWire::beginTransmission(uint8_t address) {
            //beginTransmission((uint8_t)address);
    
            // indicate that we are transmitting
            twi_transmitting = 1;
            
            // set address of targeted slave
            txAddress = address;
            
            // reset tx buffer iterator vars
            txBufferIndex = 0;
            txBufferLength = 0;
        }
        
        uint8_t TwoWire::endTransmission(uint16_t timeout) {
            // transmit buffer (blocking)
            //int8_t ret =
            twi_cbendTransmissionDone = NULL;
            twi_writeTo(txAddress, txBuffer, txBufferLength, 1);
            int8_t ret = twii_WaitForDone(timeout);
    
            // reset tx buffer iterator vars
            txBufferIndex = 0;
            txBufferLength = 0;
    
            // indicate that we are done transmitting
            // twi_transmitting = 0;
            return ret;
        }
    
        void TwoWire::nbendTransmission(void (*function)(int)) {
            twi_cbendTransmissionDone = function;
            twi_writeTo(txAddress, txBuffer, txBufferLength, 1);
            return;
        }
        
        void TwoWire::send(uint8_t data) {
            if (twi_transmitting) {
                // in master transmitter mode
                // don't bother if buffer is full
                if (txBufferLength >= NBWIRE_BUFFER_LENGTH) {
                    return;
                }
    
                // put byte in tx buffer
                txBuffer[txBufferIndex] = data;
                ++txBufferIndex;
    
                // update amount in buffer
                txBufferLength = txBufferIndex;
            } else {
                // in slave send mode
                // reply to master
                //twi_transmit(&data, 1);
            }
        }
        
        uint8_t TwoWire::receive(void) {
            // default to returning null char
            // for people using with char strings
            uint8_t value = 0;
          
            // get each successive byte on each call
            if (rxBufferIndex < rxBufferLength) {
                value = rxBuffer[rxBufferIndex];
                ++rxBufferIndex;
            }
        
            return value;
        }
        
        uint8_t TwoWire::requestFrom(uint8_t address, int quantity, uint16_t timeout) {
            // clamp to buffer length
            if (quantity > NBWIRE_BUFFER_LENGTH) {
                quantity = NBWIRE_BUFFER_LENGTH;
            }
    
            // perform blocking read into buffer
            twi_cbreadFromDone = NULL;
            twi_readFrom(address, rxBuffer, quantity);
            uint8_t read = twii_WaitForDone(timeout);
    
            // set rx buffer iterator vars
            rxBufferIndex = 0;
            rxBufferLength = read;
        
            return read;
        }
        
        void TwoWire::nbrequestFrom(uint8_t address, int quantity, void (*function)(int)) {
            // clamp to buffer length
            if (quantity > NBWIRE_BUFFER_LENGTH) {
                quantity = NBWIRE_BUFFER_LENGTH;
            }
    
            // perform blocking read into buffer
            twi_cbreadFromDone = function;
            twi_readFrom(address, rxBuffer, quantity);
            //uint8_t read = twii_WaitForDone();
    
            // set rx buffer iterator vars
            //rxBufferIndex = 0;
            //rxBufferLength = read;
    
            rxBufferIndex = 0;
            rxBufferLength = quantity; // this is a hack
    
            return; //read;
        }
    
        uint8_t TwoWire::available(void) {
            return rxBufferLength - rxBufferIndex;
        }
    
    #endif
    

    i2c.h

    // I2Cdev library collection - Main I2C device class header file
    // Abstracts bit and byte I2C R/W functions into a convenient class
    // 6/9/2012 by Jeff Rowberg <jeff@rowberg.net>
    //
    // Changelog:
    //     2012-06-09 - fix major issue with reading > 32 bytes at a time with Arduino Wire
    //                - add compiler warnings when using outdated or IDE or limited I2Cdev implementation
    //     2011-11-01 - fix write*Bits mask calculation (thanks sasquatch @ Arduino forums)
    //     2011-10-03 - added automatic Arduino version detection for ease of use
    //     2011-10-02 - added Gene Knight's NBWire TwoWire class implementation with small modifications
    //     2011-08-31 - added support for Arduino 1.0 Wire library (methods are different from 0.x)
    //     2011-08-03 - added optional timeout parameter to read* methods to easily change from default
    //     2011-08-02 - added support for 16-bit registers
    //                - fixed incorrect Doxygen comments on some methods
    //                - added timeout value for read operations (thanks mem @ Arduino forums)
    //     2011-07-30 - changed read/write function structures to return success or byte counts
    //                - made all methods static for multi-device memory savings
    //     2011-07-28 - initial release
    
    /* ============================================
    I2Cdev device library code is placed under the MIT license
    Copyright (c) 2012 Jeff Rowberg
    
    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:
    
    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.
    
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
    ===============================================
    */
    
    #ifndef _I2CDEV_H_
    #define _I2CDEV_H_
    
    // -----------------------------------------------------------------------------
    // I2C interface implementation setting
    // -----------------------------------------------------------------------------
    #define I2CDEV_IMPLEMENTATION       I2CDEV_ARDUINO_WIRE
    
    // comment this out if you are using a non-optimal IDE/implementation setting
    // but want the compiler to shut up about it
    #define I2CDEV_IMPLEMENTATION_WARNINGS
    
    // -----------------------------------------------------------------------------
    // I2C interface implementation options
    // -----------------------------------------------------------------------------
    #define I2CDEV_ARDUINO_WIRE         1 // Wire object from Arduino
    #define I2CDEV_BUILTIN_NBWIRE       2 // Tweaked Wire object from Gene Knight's NBWire project
                                          // ^^^ NBWire implementation is still buggy w/some interrupts!
    #define I2CDEV_BUILTIN_FASTWIRE     3 // FastWire object from Francesco Ferrara's project
                                          // ^^^ FastWire implementation in I2Cdev is INCOMPLETE!
    
    // -----------------------------------------------------------------------------
    // Arduino-style "Serial.print" debug constant (uncomment to enable)
    // -----------------------------------------------------------------------------
    //#define I2CDEV_SERIAL_DEBUG
    
    #ifdef ARDUINO
        #if ARDUINO < 100
            #include "WProgram.h"
        #else
            #include "Arduino.h"
        #endif
        #if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
            #include <Wire.h>
        #endif
    #else
        #include "ArduinoWrapper.h"
    #endif
    
    // 1000ms default read timeout (modify with "I2Cdev::readTimeout = [ms];")
    #define I2CDEV_DEFAULT_READ_TIMEOUT     1000
    
    class I2Cdev {
        public:
            I2Cdev();
            
            static int8_t readBit(uint8_t devAddr, uint8_t regAddr, uint8_t bitNum, uint8_t *data, uint16_t timeout=I2Cdev::readTimeout);
            static int8_t readBitW(uint8_t devAddr, uint8_t regAddr, uint8_t bitNum, uint16_t *data, uint16_t timeout=I2Cdev::readTimeout);
            static int8_t readBits(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint8_t *data, uint16_t timeout=I2Cdev::readTimeout);
            static int8_t readBitsW(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint16_t *data, uint16_t timeout=I2Cdev::readTimeout);
            static int8_t readByte(uint8_t devAddr, uint8_t regAddr, uint8_t *data, uint16_t timeout=I2Cdev::readTimeout);
            static int8_t readWord(uint8_t devAddr, uint8_t regAddr, uint16_t *data, uint16_t timeout=I2Cdev::readTimeout);
            static int8_t readBytes(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint8_t *data, uint16_t timeout=I2Cdev::readTimeout);
            static int8_t readWords(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint16_t *data, uint16_t timeout=I2Cdev::readTimeout);
    
            static bool writeBit(uint8_t devAddr, uint8_t regAddr, uint8_t bitNum, uint8_t data);
            static bool writeBitW(uint8_t devAddr, uint8_t regAddr, uint8_t bitNum, uint16_t data);
            static bool writeBits(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint8_t data);
            static bool writeBitsW(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint16_t data);
            static bool writeByte(uint8_t devAddr, uint8_t regAddr, uint8_t data);
            static bool writeWord(uint8_t devAddr, uint8_t regAddr, uint16_t data);
            static bool writeBytes(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint8_t *data);
            static bool writeWords(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint16_t *data);
    
            static uint16_t readTimeout;
    };
    
    #if I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE
        //////////////////////
        // FastWire 0.2
        // This is a library to help faster programs to read I2C devices.
        // Copyright(C) 2011
        // Francesco Ferrara
        //////////////////////
        
        /* Master */
        #define TW_START                0x08
        #define TW_REP_START            0x10
    
        /* Master Transmitter */
        #define TW_MT_SLA_ACK           0x18
        #define TW_MT_SLA_NACK          0x20
        #define TW_MT_DATA_ACK          0x28
        #define TW_MT_DATA_NACK         0x30
        #define TW_MT_ARB_LOST          0x38
    
        /* Master Receiver */
        #define TW_MR_ARB_LOST          0x38
        #define TW_MR_SLA_ACK           0x40
        #define TW_MR_SLA_NACK          0x48
        #define TW_MR_DATA_ACK          0x50
        #define TW_MR_DATA_NACK         0x58
    
        #define TW_OK                   0
        #define TW_ERROR                1
    
        class Fastwire {
            private:
                static boolean waitInt();
    
            public:
                static void setup(int khz, boolean pullup);
                static byte write(byte device, byte address, byte value);
                static byte readBuf(byte device, byte address, byte *data, byte num);
        };
    #endif
    
    #if I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE
        // NBWire implementation based heavily on code by Gene Knight <Gene@Telobot.com>
        // Originally posted on the Arduino forum at http://arduino.cc/forum/index.php/topic,70705.0.html
        // Originally offered to the i2cdevlib project at http://arduino.cc/forum/index.php/topic,68210.30.html
    
        #define NBWIRE_BUFFER_LENGTH 32
        
        class TwoWire {
            private:
                static uint8_t rxBuffer[];
                static uint8_t rxBufferIndex;
                static uint8_t rxBufferLength;
            
                static uint8_t txAddress;
                static uint8_t txBuffer[];
                static uint8_t txBufferIndex;
                static uint8_t txBufferLength;
            
                // static uint8_t transmitting;
                static void (*user_onRequest)(void);
                static void (*user_onReceive)(int);
                static void onRequestService(void);
                static void onReceiveService(uint8_t*, int);
        
            public:
                TwoWire();
                void begin();
                void begin(uint8_t);
                void begin(int);
                void beginTransmission(uint8_t);
                //void beginTransmission(int);
                uint8_t endTransmission(uint16_t timeout=0);
                void nbendTransmission(void (*function)(int)) ;
                uint8_t requestFrom(uint8_t, int, uint16_t timeout=0);
                //uint8_t requestFrom(int, int);
                void nbrequestFrom(uint8_t, int, void (*function)(int));
                void send(uint8_t);
                void send(uint8_t*, uint8_t);
                //void send(int);
                void send(char*);
                uint8_t available(void);
                uint8_t receive(void);
                void onReceive(void (*)(int));
                void onRequest(void (*)(void));
        };
        
        #define TWI_READY   0
        #define TWI_MRX     1
        #define TWI_MTX     2
        #define TWI_SRX     3
        #define TWI_STX     4
        
        #define TW_WRITE    0
        #define TW_READ     1
        
        #define TW_MT_SLA_NACK      0x20
        #define TW_MT_DATA_NACK     0x30
        
        #define CPU_FREQ            16000000L
        #define TWI_FREQ            100000L
        #define TWI_BUFFER_LENGTH   32
        
        /* TWI Status is in TWSR, in the top 5 bits: TWS7 - TWS3 */
        
        #define TW_STATUS_MASK              (_BV(TWS7)|_BV(TWS6)|_BV(TWS5)|_BV(TWS4)|_BV(TWS3))
        #define TW_STATUS                   (TWSR & TW_STATUS_MASK)
        #define TW_START                    0x08
        #define TW_REP_START                0x10
        #define TW_MT_SLA_ACK               0x18
        #define TW_MT_SLA_NACK              0x20
        #define TW_MT_DATA_ACK              0x28
        #define TW_MT_DATA_NACK             0x30
        #define TW_MT_ARB_LOST              0x38
        #define TW_MR_ARB_LOST              0x38
        #define TW_MR_SLA_ACK               0x40
        #define TW_MR_SLA_NACK              0x48
        #define TW_MR_DATA_ACK              0x50
        #define TW_MR_DATA_NACK             0x58
        #define TW_ST_SLA_ACK               0xA8
        #define TW_ST_ARB_LOST_SLA_ACK      0xB0
        #define TW_ST_DATA_ACK              0xB8
        #define TW_ST_DATA_NACK             0xC0
        #define TW_ST_LAST_DATA             0xC8
        #define TW_SR_SLA_ACK               0x60
        #define TW_SR_ARB_LOST_SLA_ACK      0x68
        #define TW_SR_GCALL_ACK             0x70
        #define TW_SR_ARB_LOST_GCALL_ACK    0x78
        #define TW_SR_DATA_ACK              0x80
        #define TW_SR_DATA_NACK             0x88
        #define TW_SR_GCALL_DATA_ACK        0x90
        #define TW_SR_GCALL_DATA_NACK       0x98
        #define TW_SR_STOP                  0xA0
        #define TW_NO_INFO                  0xF8
        #define TW_BUS_ERROR                0x00
        
        //#define _MMIO_BYTE(mem_addr) (*(volatile uint8_t *)(mem_addr))
        //#define _SFR_BYTE(sfr) _MMIO_BYTE(_SFR_ADDR(sfr))
        
        #ifndef sbi // set bit
            #define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
        #endif // sbi
        
        #ifndef cbi // clear bit
            #define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
        #endif // cbi
        
        extern TwoWire Wire;
    
    #endif // I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_NBWIRE
    
    #endif /* _I2CDEV_H_ */

    I would appreciate it if I heard from you.

  • This is a question that I need to think about again.

    I also want to ask what is the formula for converting the data read from the capacitance data registers into the capacitor value.

    Most of the programs in this part are consistent, but the later conversion of the read data into the actual capacitance value, the formula is different, can you give me some guidance.
    for example:


    I haven't found a pattern that I would like you to guide me
    Thanks.

  • From the datasheet description of the 24-bit cap data register:

    The 0x000000 code represents negative full scale (–4.096 pF), the 0x800000 code represents zero scale (0 pF), and the 0xFFFFFF code represents positive full scale (+4.096 pF).

    This is offset binary. You can subtract 0x800000 first, which will result in a signed, 2s complement number. Be careful that the sign extension is done properly if you are using a 32-bit word.

    then multiply the result by the value of one lsb, which would be 4.096 pF / 8388608

    It is a good idea to double-check your math by passing known values to it, and make sure it returns the expected result. (for example, sending digital code zero, 0x800000, 0xFFFFFF should return -4.096, 0, and 4.096, respectively.

    -Mark

  • hi,Mark
    I tried your suggestion today and still don't get the results I want.

    this is my head file.

    // I2Cdev library collection - AD7746 I2C device class header file
    // Based on Analog Devices AD7746 Datasheet, Revision 0, 2005
    // 2012-04-01 by Peteris Skorovs <pskorovs@gmail.com>
    //
    // This I2C device library is using (and submitted as a part of) Jeff Rowberg's I2Cdevlib library,
    // which should (hopefully) always be available at https://github.com/jrowberg/i2cdevlib
    //
    // Changelog:
    //     2012-04-01 - initial release
    
    /* ============================================
    I2Cdev device library code is placed under the MIT license
    Copyright (c) 2012 Peteris Skorovs
    
    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:
    
    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.
    
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
    ===============================================
    */
    
    #ifndef _AD7746_H_
    #define _AD7746_H_
    
    #include "I2Cdev.h"
    
    
    #define AD7746_ADDRESS           0x48
    #define AD7746_DEFAULT_ADDRESS   AD7746_ADDRESS           
    
    
    #define AD7746_RA_STATUS                 0x00 // Status
    #define AD7746_RA_CAP_DATA_H             0x01 // Cap data
    #define AD7746_RA_CAP_DATA_M             0x02 // Cap data
    #define AD7746_RA_CAP_DATA_L             0x03 // Cap data
    #define AD7746_RA_VT_DATA_H              0x04 // VT data
    #define AD7746_RA_VT_DATA_M              0x05 // VT data
    #define AD7746_RA_VT_DATA_L              0x06 // VT data
    #define AD7746_RA_CAP_SETUP              0x07 // Cap Setup
    #define AD7746_RA_VT_SETUP               0x08 // VT Setup
    #define AD7746_RA_EXC_SETUP              0x09 // Exc Setup
    #define AD7746_RA_CONFIGURATION          0x0A // Configuration
    #define AD7746_RA_CAP_DAC_A              0x0B // Cap DAC A
    #define AD7746_RA_CAP_DAC_B              0x0C // Cap DAC B
    #define AD7746_RA_CAP_OFF_H              0x0D 
    #define AD7746_RA_CAP_OFF_L              0x0E 
    #define AD7746_RA_CAP_GAIN_H             0x0F
    #define AD7746_RA_CAP_GAIN_L             0x10
    #define AD7746_RA_VOLT_GAIN_H            0x11
    #define AD7746_RA_VOLT_GAIN_L            0x12
    
    #define AD7746_RESET                     0xBF
    
    // Status
    #define AD7746_EXCERR_BIT                3
    #define AD7746_RDY_BIT		             2
    #define AD7746_RDYVT_BIT                 1
    #define AD7746_RDYCAP_BIT                0
    
    // Cap Setup
    #define AD7746_CAPEN_BIT                 7
    #define AD7746_CIN2_BIT                  6
    #define AD7746_CAPDIFF_BIT               5
    #define AD7746_CACHOP_BIT                0
    
    #define AD7746_CAPEN                     (1 << AD7746_CAPEN_BIT)
    #define AD7746_CIN2                      (1 << AD7746_CIN2_BIT)
    
    // VT Setup
    #define AD7746_VTEN_BIT                  7
    #define AD7746_VTMD_BIT_1                6
    #define AD7746_VTMD_BIT_0                5
    #define AD7746_EXTREF_BIT                4
    #define AD7746_VTSHORT_BIT               1
    #define AD7746_VTCHOP_BIT	             0
    
    #define AD7746_VTEN                      (1 << AD7746_VTEN_BIT)
    
    #define AD7746_VTMD_INT_TEMP             0
    #define AD7746_VTMD_EXT_TEMP             (1 << AD7746_VTMD_BIT_0)
    #define AD7746_VTMD_VDD_MON              (1 << AD7746_VTMD_BIT_1)
    #define AD7746_VTMD_VIN                  (1 << AD7746_VTMD_BIT_1) | (1 << AD7746_VTMD_BIT_0)
    
    // Exc Setup
    #define AD7746_CLKCTRL_BIT		         7 
    #define AD7746_EXCON_BIT		         6                                            
    #define AD7746_EXCB_BIT		             5
    #define AD7746_INV_EXCB_BIT		         4
    #define AD7746_EXCA_BIT		             3
    #define AD7746_INV_EXCA_BIT		         2
    #define AD7746_EXCLVL_BIT_1              1
    #define AD7746_EXCLVL_BIT_0              0
    
    #define AD7746_EXCA                      (1 << AD7746_EXCA_BIT)
    #define AD7746_EXCB                      (1 << AD7746_EXCB_BIT)
    #define AD7746_EXCON                     (1 << AD7746_EXCON_BIT)
    
    #define AD7746_EXCLVL_VDD_X_1_8          0
    #define AD7746_EXCLVL_VDD_X_1_4          (1 << AD7746_EXCLVL_BIT_0)
    #define AD7746_EXCLVL_VDD_X_3_8          (1 << AD7746_EXCLVL_BIT_1)
    #define AD7746_EXCLVL_VDD_X_1_2          (1 << AD7746_EXCLVL_BIT_1) | (1 << AD7746_EXCLVL_BIT_0)
    
    // Configuration
    #define AD7746_VTF_BIT_1                 7
    #define AD7746_VTF_BIT_0                 6
    #define AD7746_CAPF_BIT_2                5
    #define AD7746_CAPF_BIT_1                4
    #define AD7746_CAPF_BIT_0                3
    #define AD7746_MD_BIT_2                  2
    #define AD7746_MD_BIT_1                  1
    #define AD7746_MD_BIT_0                  0
    
    #define AD7746_VTF_20P1                  0
    #define AD7746_VTF_32P1                  (1 << AD7746_VTF_BIT_0)
    #define AD7746_VTF_62P1                  (1 << AD7746_VTF_BIT_1)
    #define AD7746_VTF_122P1                 (1 << AD7746_VTF_BIT_1) | (1 << AD7746_VTF_BIT_0)
    
    #define AD7746_CAPF_11P0                 0
    #define AD7746_CAPF_11P9                 (1 << AD7746_CAPF_BIT_0)
    #define AD7746_CAPF_20P0                 (1 << AD7746_CAPF_BIT_1)
    #define AD7746_CAPF_38P0                 (1 << AD7746_CAPF_BIT_1) | (1 << AD7746_CAPF_BIT_0)
    #define AD7746_CAPF_62P0                 (1 << AD7746_CAPF_BIT_2)
    #define AD7746_CAPF_77P0                 (1 << AD7746_CAPF_BIT_2) | (1 << AD7746_CAPF_BIT_0)
    #define AD7746_CAPF_92P0                 (1 << AD7746_CAPF_BIT_2) | (1 << AD7746_CAPF_BIT_1)
    #define AD7746_CAPF_109P6                (1 << AD7746_CAPF_BIT_2) | (1 << AD7746_CAPF_BIT_1) | (1 << AD7746_CAPF_BIT_0)
    
    #define AD7746_MD_IDLE                   0
    #define AD7746_MD_CONTINUOUS_CONVERSION  (1 << AD7746_MD_BIT_0)
    #define AD7746_MD_SINGLE_CONVERSION      (1 << AD7746_MD_BIT_1)
    #define AD7746_MD_POWER_DOWN             (1 << AD7746_MD_BIT_1) | (1 << AD7746_MDF_BIT_0)
    #define AD7746_MD_OFFSET_CALIBRATION     (1 << AD7746_MD_BIT_2) | (1 << AD7746_MD_BIT_0)
    #define AD7746_MD_GAIN_CALIBRATION       (1 << AD7746_MD_BIT_2) | (1 << AD7746_MD_BIT_1)
    
    // Cap DAC A
    #define AD7746_DACAEN_BIT                7
    
    #define AD7746_DACAEN                    (1 << AD7746_DACAEN_BIT)
    
    // Cap DAC B
    #define AD7746_DACBEN_BIT                7
    
    #define AD7746_DACBEN                    (1 << AD7746_DACBEN_BIT)
    
    
    #define AD7746_DAC_COEFFICIENT           0.13385826771654F // 17pF/127
    
    
    
    class AD7746 {
        public:
            AD7746();
            AD7746(uint8_t address);
    
            void initialize();
            bool testConnection();
            void reset(); 
    
           float getCapacitance();
            //double CAPvalue();
        
            void writeCapSetupRegister(uint8_t data);
            void writeVtSetupRegister(uint8_t data);
            void writeExcSetupRegister(uint8_t data);
            void writeConfigurationRegister(uint8_t data);
            void writeCapDacARegister(uint8_t data);
            void writeCapDacBRegister(uint8_t data);
            
    
        private:
            uint8_t devAddr;
            uint8_t buffer[19];
    };
    
    #endif /* _AD7746_H_ */
    

    float AD7746::getCapacitance() {
      uint32_t capacitance;
      float capacitance1;
      I2Cdev::readBytes(devAddr,0x01,3,buffer);
      capacitance = ((uint32_t)buffer[1] << 16) | ((uint32_t)buffer[2] << 8) | (uint32_t)buffer[3];
      // C=ieee_float(capacitance);
      capacitance1= (-0x80+(float)capacitance)*(4.096/8388608);
      return capacitance1;
    }

    This is the part of the capacitor value conversion in the source file using arduino and AD7746.
    1.I can't get decimal values, even if I change to float format.

    Without adding the formula you provided to me, 1pF output result.

    2.When I use the 1pF capacitor value, the output is shown above; When I take 5pF the output is 6pF if this is due to overrange.
    3.I don't quite understand whether the CAP DAC registers function in line with the CAPDAC function.

    Thank you for reading and look forward to your reply as soon as possible.

  • You might want to break things up into a couple of steps. Here's a similar function for an ADC that has an offset binary format:

    https://github.com/analogdevicesinc/Linduino/blob/master/LTSketchbook/libraries/LTC24XX_general/LTC24XX_general.cpp#L389

    I think you need to subtract the 0x800000 offset first, before casting as a float; you're doing this in a single step and I'm not sure what the result will be.

    (Also it looks like you're subtracting 0x80, not 0x800000).

    Try making a small test program that only exercises that formula, step through a range of input values, and make sure the output is as expected. That way you can debug this completely independently of the actual part.

    -Mark

  • HI,Mark!
    When I don't put a capacitor between EXCA and CIN(+), I have more than 1pF of capacitance between the breadboard holes. Is this because of the stray capacitance between the breadboards, can I calibrate to get the results I want?

    The top half is the result of adding a 1pF capacitor in the middle.
    The lower half is where no capacitor is applied.
    By the way, when I subtract 0x80000, my capacitance value becomes large.


  • The procedure for calibrating an offset is described on page 23 of the AD7746 datasheet, and it's noted that board level stray capacitances often dominate.

    Not sure how to explain the subtraction error - although you're mentioning 0x80000, with four zeros, should it be 0x800000 (an 8 with five zeros)?

    -Mark

  • hi,mark.
    thanks for your help.
    I read in the file.I should first do the calibration of on-chip CAPDACs.  .Is this the value of setting DACA? 


    1 When I want to use a single-ended capacitor input, should I set the value of DACA to 4.096pf when the output range of the capacitor is 0-8.192pf.  or  Use the following formula to set the DACA value.This formula appears in the circuit description of the CN0552.

    2.Are subtractions from the above questions necessary in all cases 0x800000.

  • Hi Ikxaaa,

    It sounds like you're over most of your difficulty with the driver and reading /writing / interpreting data. Can you either move this thread to the  Precision ADCs forum, or start a new question specific to your calibration question? There are several answered questions on related topics, for example:

     AD7746 Calibration 

     AD7746 measurement problem 

     AD7745/AD7746 Cables and parasitic capacitance to ground 

    -Mark 

  • FormerMember
    0 FormerMember
in reply to MarkThoren

Per Mark's comment I agree that this question has been fundamentally answered.  And will be closed out.  There are several threads that Mark linked you to talking about the calibration routine which you should read over as a starting point, but if that doesn't answer your question, please submit a new question in the  Precision ADCs forum for a more accurate answer. 

  • I'm going to go to these places and ask questions. Thank you for your help.

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