MMA8453 accelerometer I2C problem

Question

I ran into an issue with my project. I use Renesas RL78 microcontroller and on one I2C bus I have two sensors: digital compass and accelerometer. Accelerometer type is MMA8453 by Freescale.

Datasheet: http://cache.freescale.com/files/sensors/doc/data_sheet/MMA8453Q.pdf

I have no problem with reading data from compass. Accelerometer, however, is a different story. I can't read anything from it - at least I guess I'm not getting anything. Unfortunately I don't have scope or logic analyzer to check out. I get an ACK, but no data.

Here is the function I use for reading register of I2C device:

uint8_t Read_I2C_Sensor_Reg(uint8_t DevAddr, uint8_t RegAddr, uint8_t *Data, uint8_t Numbytes, uint8_t wait)
{
    uint16_t status = 0;
    uint16_t timeout = 1000; //approx 32uSec
    DevAddr <<= 1;      //Shifting left by one bit to make room for Read/Write bit

    IICA0_Err = 0;
    IICA0_Tx_Done |= 1;
    status = IICA0_Master_Send(DevAddr, &RegAddr, 1,  wait);
    while(IICA0_Tx_Done)
    {
        while(timeout--);
        iica0_master_check_status();    //<SCH> checking the transation status, in case if this fails, report andre initiate transaction.
        if(IICA0_Err)
        {
            status = IICA0_Err ; break;
        }
    }
    if (IICA0_Tx_Done == 0)
    {
        IICA0_StopCondition();
        while (SPD0 == 0);

        IICA0_Rx_Done |= 1;
        status = IICA0_Master_Receive(DevAddr, Data, Numbytes,  wait);
        while(IICA0_Rx_Done)
        {
            while(timeout--);
            iica0_master_check_status();
            if(IICA0_Err)
            {
                status = IICA0_Err ; break;
            }
        }

        if (IICA0_Tx_Done == 0)
        {
            IICA0_StopCondition();
            while (SPD0 == 0);
        }
    }

    if (status == MD_OK)
      return 0;
    else
      return 1;
}

Did anyone come across this kind of issue? I can post more details later, if needed.

Answer 1

Based on the fact that you able to communicate with one i2c sensor but not another, I would start investing the following:

Focus on reading the WHO_AM_I register because it is a simple test for reads and the answer 0x3A is fixed.

• Check that the slave's I2C address matches the hardware, i.e. is the pin SA0 pulled high or low? Are you using the slave address 0x1C or 0x1D?
• Check that you are terminating your reads with NACK. A master's read sequence must end in a NACK according to I2C, but not all vendors care too much. IIRC Freescale does.
• Check the I2C bus length and pullups, i.e. if you have more than a few cm of cable, your pullups should be for example 1k rather than 10k. This will depend on the timing etc characteristics of the device.

I've written a blog post about I2C a while ago where I've also outlined common I2C problems and given more details: http://chipscoop.blogspot.fi/2012/08/understanding-ic-and-some-typical-uses.html