main.cpp

00001 /*Program Example 7.4: Reads values from accelerometer through SPI, and outputs 
00002 continuously to terminal screen.
00003 */
00004 
00005 #include "mbed.h"
00006 SPI acc(p11,p12,p13);            // set up SPI interface on pins 11,12,13
00007 DigitalOut cs(p14);              // use pin 14 as chip select      
00008 Serial pc(USBTX, USBRX);         // set up USB interface to host terminal
00009 char buffer[6];                  //raw data array type char
00010 int16_t data[3];                 // 16-bit twos-complement integer data
00011 float x, y, z;                   // floating point data, to be displayed on-screen
00012 
00013 int main() {
00014   cs=1;                        //initially ADXL345 is not activated
00015   acc.format(8,3);             // 8 bit data, Mode 3
00016   acc.frequency(2000000);      // 2MHz clock rate
00017   cs=0;                        //select the device
00018   acc.write(0x31);             // data format register
00019   acc.write(0x0B);             // format +/-16g, 0.004g/LSB
00020   cs=1;                        //end of transmission
00021   cs=0;                        //start a new transmission
00022   acc.write(0x2D);             // power ctrl register
00023   acc.write(0x08);             // measure mode
00024   cs=1;                        //end of transmission
00025   while (1) {                  // infinite loop
00026     wait(0.2);
00027     cs=0;                      //start a transmission
00028     acc.write(0x80|0x40|0x32);   // RW bit high, MB bit high, plus address
00029     for (int i = 0;i<=5;i++) {
00030       buffer[i]=acc.write(0x00);       // read back 6 data bytes
00031     }
00032     cs=1;                      //end of transmission
00033     data[0] = buffer[1]<<8 | buffer[0];  // combine MSB and LSB
00034     data[1] = buffer[3]<<8 | buffer[2];
00035     data[2] = buffer[5]<<8 | buffer[4];       
00036     x=0.004*data[0]; y=0.004*data[1]; z=0.004*data[2]; // convert to float, 
00037                                                        //actual g value
00038     pc.printf("x = %+1.2fg\t y = %+1.2fg\t z = %+1.2fg\n\r", x, y,z); //print 
00039   }
00040 }
00041