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Original question:

SPI communication with Accelerometer

CCS/RM46L852: Interfacing ADXL345 accelerometer with RM46L852 controller.

Rahul Achar
Prodigy 70 points
Part Number: RM46L852
Other Parts Discussed in Thread: HALCOGEN

Tool/software: Code Composer Studio

Hello everyone,

I have been trying to interface accelerometer  ADXL345 ( https://www.analog.com/media/en/technical-documentation/data-sheets/ADXL345.pdf ) with RM46L852 controller ( http://www.ti.com/lit/ds/spns185c/spns185c.pdf ) using SPI communication (SPI4) for acquiring the accelerometer data from ADXL345. I am using HALCoGen to generate the SPI driver. Code Composer Studio (CCS) is used.

The results that are obtained are inconsistent and it picks up negative values when I place the accelerometer in positive Z axis. 

Please help me in this regard. Thank you.

The code in CCS is as follows:

/* USER CODE BEGIN (0) */
/* USER CODE END */
/* Include Files */
#include "sys_common.h"
/* USER CODE BEGIN (1) */
#include"spi.h"
#include"pinmux.h"
#include"stdio.h"
/* USER CODE END */
/* USER CODE BEGIN (2) */
uint16 X0,X1,Y0,Y1,Z0,Z1;
        uint16 i,j,k;
uint16 TX_Data_Master, RX_Data_Master;
        short int x,y,z;
        float Xg,Yg,Zg;
        float X[3200]={0x00};
        float Y[3200]={0x00};
        float Z[3200]={0x00};
/* USER CODE END */
int main(void)
{
/* USER CODE BEGIN (3) */
    uint16 TX_Data_Master[8] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
    uint16 RX_Data_Master[8] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
    spiDAT1_t dataconfig1_t;
            dataconfig1_t.CS_HOLD = FALSE; //DEFAULT CONFIGURATION FOR SPI
            dataconfig1_t.WDEL    = TRUE; //WAIT DELAY
            dataconfig1_t.DFSEL   = SPI_FMT_0;
            dataconfig1_t.CSNR    = 0xFE; // CHIP SELECT NUMBER
    /* {
                SPI_CS_NONE = 0xFFU,
                SPI_CS_0    = 0xFEU,
                SPI_CS_1    = 0xFDU,
                SPI_CS_2    = 0xFBU,
                SPI_CS_3    = 0xF7U,
                SPI_CS_4    = 0xEFU,
                SPI_CS_5    = 0xDFU,
                SPI_CS_6    = 0xBFU,
                SPI_CS_7    = 0x7FU
            };*/
    spiInit();// FOR INITIALIZATION of spi driver and module
    for(i=0;i<6;i++)
            {
             //0X2C IS FOR OUTPUT DATA RATE-BW_RATE REGISTER
                TX_Data_Master[i] = 0x2CFF;//1F ALSO DOES THE SAME WORK -FF OR 1F MEANS IT WORKS IN REDUCED  POWER MODEAND0F MEANS IT IS FOR NORMAL OPERATION
               spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
               //0X2D IS FOR POWER CONTRL REGISTER
               TX_Data_Master[i] = 0x2D00;// INITIALLY WE MAKE IT AS ZERO
               spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
               //0X31 IS FOR THE DATA FORMAT REGISTER
               TX_Data_Master[i] = 0x3101;
               spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
               TX_Data_Master[i] = 0x2D16;//HERE WE ARE CONFIGURING AUTOSLEEP,SLEEP AND WAKEUP
               spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
              TX_Data_Master[i] = 0x2D08;//HERE WE ARE SELECTING THE MEASURE BIT IN THE POWER CONTROL REGISTER
              spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
            }
    for(j=0;j<3200;j++)
    //while(1)
    {
    TX_Data_Master[0] = 0xF200;
    spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
    X0=RX_Data_Master[0];
    TX_Data_Master[0] = 0xF300;
    spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
     X1=RX_Data_Master[0];
    TX_Data_Master[0] = 0xF400;
    spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
    Y0=RX_Data_Master[0];
    TX_Data_Master[0] = 0xF500;
    spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
    Y1=RX_Data_Master[0];
    TX_Data_Master[0] = 0xF600;
    spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
     Z0=RX_Data_Master[0];
    TX_Data_Master[0] = 0xF700;
    spiTransmitAndReceiveData(spiREG4, &dataconfig1_t, 1, TX_Data_Master, RX_Data_Master);
    Z1=RX_Data_Master[0];
    x= (X1<<8) | X0;
    y= (Y1<<8) | Y0;
    z= (Z1<<8) | Z0;
    Xg=x*0.0078;
    Yg=y*0.0078;
    Zg=z*0.0078;
       Z[j]=Zg;
       X[j]=Xg;
       Y[j]=Yg;
  printf ("%1.2f %1.2f %1.2f \n",Zg,Yg,Xg);
            }
/* USER CODE END */
    return 0;
}
/* USER CODE BEGIN (4) */
/* USER CODE END */

 The HALCoGen settings for the SPI4 driver is as follows:

  • 0
    TI__Guru**** 197336 points

    Hello,

    Do you follow the SPI communication requirements from ADXL345 datasheet? What happens if you decrease the SPI clock? What is the return value if your read the register 0 (DEVID)?

    "The maximum SPI clock speed is 5 MHz with 100 pF maximum loading, and the timing scheme follows clock polarity (CPOL) = 1 and clock phase (CPHA) = 1"

  • 0 in reply to QJ Wang
    Prodigy 70 points

    Hello,

    Do you follow the SPI communication requirements from ADXL345 datasheet? What happens if you decrease the SPI clock? What is the return value if your read the register 0 (DEVID)?

    "The maximum SPI clock speed is 5 MHz with 100 pF maximum loading, and the timing scheme follows clock polarity (CPOL) = 1 and clock phase (CPHA) = 1"

    Hello Wang,

    Yes, I have followed the SPI Communication requirements according to the datasheet.

    I'm able to read the DEVICE ID = E5 only when I set the clock polarity (CPOL) = 1 and clock phase (CPHA) = 0 and not when clock polarity (CPOL) = 1 and clock phase (CPHA) = 1.

    I am able to get the results even in the decreased SPI clock frequencies.

    And when I acquire the data from the accelerometer ADXL345 placing in the positive Z axis, it is picking negative values along with positive values. I have added the snapshot below. 

    Let me know if I am going wrong anywhere. The code used is put up in the first query.

     Thanks and Regards

    Rahul Achar

  • 0 in reply to Rahul Achar
    TI__Guru**** 197336 points

    Hello Rahul,

    ADXL345 is to measure both dynamic acceleration resulting from motion or shock and static acceleration, such as gravity. Placing  ADXL345 in the positive Z axis doesn't mean that the acceleration is positive.

  • 0 in reply to QJ Wang
    Prodigy 70 points

    QJ Wang said:

    Hello Rahul,

    ADXL345 is to measure both dynamic acceleration resulting from motion or shock and static acceleration, such as gravity. Placing  ADXL345 in the positive Z axis doesn't mean that the acceleration is positive.

    Hello Wang, 

    The result which I have posted previously is the static acceleration obtained when ADXL345 was place on a table in the positive Z-axis. It wasn't subjected to any excitation or motion. 

    When I measured the static acceleration in the negative axis directions of X,Y,Z I'm getting negative values without any positive value. 

    Thanks and Regards

    Rahul Achar 

  • 0 in reply to Rahul Achar
    TI__Guru**** 197336 points

    Hello,

    The SPI_MISO reads what the sensor outputs. The device ID is read correctly. I don't think the error (if it is a error) is caused by the SPI driver.