arduino中用IIC读取MMA8452三轴加速度模块数据

http://www.geek-workshop.com/thread-898-1-1.html

/*

MMA8452Q Basic Example Code

Nathan Seidle

SparkFun Electronics

November 5, 2012

License: This code is public domain but you buy me a beer if you use this and we meet someday (Beerware license).

This example code shows how to read the X/Y/Z accelerations and basic functions of the MMA5842. It leaves out

all the neat features this IC is capable of (tap, orientation, and inerrupts) and just displays X/Y/Z. See

the advanced example code to see more features.

Hardware setup:

MMA8452 Breakout ------------ Arduino

3.3V --------------------- 3.3V

SDA -------^^(330)^^------- A4

SCL -------^^(330)^^------- A5

GND ---------------------- GND

The MMA8452 is 3.3V so we recommend using 330 or 1k resistors between a 5V Arduino and the MMA8452 breakout.

The MMA8452 has built in pull-up resistors for I2C so you do not need additional pull-ups.

*/

#include <Wire.h> // Used for I2C

// The SparkFun breakout board defaults to 1, set to 0 if SA0 jumper on the bottom of the board is set

#define MMA8452_ADDRESS 0x1D // 0x1D if SA0 is high, 0x1C if low

//Define a few of the registers that we will be accessing on the MMA8452

#define OUT_X_MSB 0x01

#define XYZ_DATA_CFG 0x0E

#define WHO_AM_I 0x0D

#define CTRL_REG1 0x2A

#define GSCALE 2 // Sets full-scale range to +/-2, 4, or 8g. Used to calc real g values.

void setup()

{

Serial.begin(9600);

Serial.println("MMA8452 Basic Example");

Wire.begin(); //Join the bus as a master

initMMA8452(); //Test and intialize the MMA8452

}

void loop()

{

int accelCount[3]; // Stores the 12-bit signed value

readAccelData(accelCount); // Read the x/y/z adc values

// Now we'll calculate the accleration value into actual g's

float accelG[3]; // Stores the real accel value in g's

for (int i = 0 ; i < 3 ; i++)

{

accelG[i] = (float) accelCount[i] / ((1<<12)/(2*GSCALE)); // get actual g value, this depends on scale being set

}

// Print out values

for (int i = 0 ; i < 3 ; i++)

{

Serial.print(accelG[i], 4); // Print g values

Serial.print("\t"); // tabs in between axes

}

Serial.println();

delay(10); // Delay here for visibility

}

void readAccelData(int *destination)

{

byte rawData[6]; // x/y/z accel register data stored here

readRegisters(OUT_X_MSB, 6, rawData); // Read the six raw data registers into data array

// Loop to calculate 12-bit ADC and g value for each axis

for(int i = 0; i < 3 ; i++)

{

int gCount = (rawData[i*2] << 8) | rawData[(i*2)+1]; //Combine the two 8 bit registers into one 12-bit number

gCount >>= 4; //The registers are left align, here we right align the 12-bit integer

// If the number is negative, we have to make it so manually (no 12-bit data type)

if (rawData[i*2] > 0x7F)

{

gCount = ~gCount + 1;

gCount *= -1; // Transform into negative 2's complement #

}

destination[i] = gCount; //Record this gCount into the 3 int array

}

}

// Initialize the MMA8452 registers

// See the many application notes for more info on setting all of these registers:

// http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MMA8452Q
void initMMA8452()

{

byte c = readRegister(WHO_AM_I); // Read WHO_AM_I register

if (c == 0x2A) // WHO_AM_I should always be 0x2A

{

Serial.println("MMA8452Q is online...");

}

else

{

Serial.print("Could not connect to MMA8452Q: 0x");

Serial.println(c, HEX);

while(1) ; // Loop forever if communication doesn't happen

}

MMA8452Standby(); // Must be in standby to change registers

// Set up the full scale range to 2, 4, or 8g.

byte fsr = GSCALE;

if(fsr > 8) fsr = 8; //Easy error check

fsr >>= 2; // Neat trick, see page 22. 00 = 2G, 01 = 4A, 10 = 8G

writeRegister(XYZ_DATA_CFG, fsr);

//The default data rate is 800Hz and we don't modify it in this example code

MMA8452Active(); // Set to active to start reading

}

// Sets the MMA8452 to standby mode. It must be in standby to change most register settings

void MMA8452Standby()

{

byte c = readRegister(CTRL_REG1);

writeRegister(CTRL_REG1, c & ~(0x01)); //Clear the active bit to go into standby

}

// Sets the MMA8452 to active mode. Needs to be in this mode to output data

void MMA8452Active()

{

byte c = readRegister(CTRL_REG1);

writeRegister(CTRL_REG1, c | 0x01); //Set the active bit to begin detection

}

// Read bytesToRead sequentially, starting at addressToRead into the dest byte array

void readRegisters(byte addressToRead, int bytesToRead, byte * dest)

{

Wire.beginTransmission(MMA8452_ADDRESS);

Wire.write(addressToRead);

Wire.endTransmission(false); //endTransmission but keep the connection active

Wire.requestFrom(MMA8452_ADDRESS, bytesToRead); //Ask for bytes, once done, bus is released by default

while(Wire.available() < bytesToRead); //Hang out until we get the # of bytes we expect

for(int x = 0 ; x < bytesToRead ; x++)

dest[x] = Wire.read();

}

// Read a single byte from addressToRead and return it as a byte

byte readRegister(byte addressToRead)

{

Wire.beginTransmission(MMA8452_ADDRESS);

Wire.write(addressToRead);

Wire.endTransmission(false); //endTransmission but keep the connection active

Wire.requestFrom(MMA8452_ADDRESS, 1); //Ask for 1 byte, once done, bus is released by default

while(!Wire.available()) ; //Wait for the data to come back

return Wire.read(); //Return this one byte

}

// Writes a single byte (dataToWrite) into addressToWrite

void writeRegister(byte addressToWrite, byte dataToWrite)

{

Wire.beginTransmission(MMA8452_ADDRESS);

Wire.write(addressToWrite);

Wire.write(dataToWrite);

Wire.endTransmission(); //Stop transmitting

}