LAUNCHXL-CC2650: MPU9250 not initializing

Tony Blake

Part Number: LAUNCHXL-CC2650
Other Parts Discussed in Thread: CC2650STK, CC2650,

Hi,

I'm trying to interface an MPU9250 IMU with a CC2650 LaunchPad using the SensorTag project (cc2650stk). The IMU is connected to the LaunchPad via the I2C bus but will not initialize when the program is run. I've stepped through the code and can see that the WHO_AM_I register on the MPU9250 is not being set to 0x71 as it should be (it is not being set at all). I've double checked that the I2C wiring is correct and have connected the AD0 pin on the MPU9250 to GND as described in the datasheet (although I don't understand this).

Can anyone help me with this? What should I do next?

Cheers,

Tony

over 8 years ago

0 Klas Lofstedt over 8 years ago

TI__Intellectual 1945 points

Hi Tony,

Just to double check if you're aware that the SensorTag project and LaunchPad has different board files, so the I2C pinout might not be the same. Apart from that i would suggest you hook up a logic analyzer to read the I2C pins to see if they are transmitting or if it's the MPU that is faulty.

Regards,

Klas

0 YiKai Chen over 8 years ago

Guru 735685 points

Do you use scope to check if there is signal on I2C SCK and SDA pins?

0 Christin Lee over 8 years ago

TI__Guru 56215 points

Can you provide the logic analyzer trace of the I2C signal?

0 Tony Blake over 8 years ago in reply to Christin Lee

Intellectual 600 points

Hi guys,

I've switched the board.h file in my project to that used in the cc2650lp project but still can't initialize the IMU. I've tried measuring the SCL signal coming off the LaunchPad pin using a scope but am just getting noise:

Is there a reason why I would not be getting a SCL signal?

Tony

0 YiKai Chen over 8 years ago in reply to Tony Blake

Guru 735685 points

Which I2C SCL/SDA pins do you use on LAUNCHXL-CC2650 to connect to MPU-9250?

0 Tony Blake over 8 years ago in reply to YiKai Chen

Intellectual 600 points

DIO4 for SCL and DIO5 for SDA

0 YiKai Chen over 8 years ago in reply to Tony Blake

Guru 735685 points

Do you add pull-high to SCL and SDA?

0 Tony Blake over 8 years ago in reply to YiKai Chen

Intellectual 600 points

There are already pull-up resistors on the board:

0 YiKai Chen over 8 years ago in reply to Tony Blake

Guru 735685 points

But it doesn't show pull high in your scope screenshot.

0 Tony Blake over 8 years ago in reply to YiKai Chen

Intellectual 600 points

I've just checked with a multimeter and both pins are pulled high to 3.3 V

0 YiKai Chen over 8 years ago in reply to Tony Blake

Guru 735685 points

You should check your scope settings so we can make sure it captures correct results.

0 Tony Blake over 8 years ago in reply to Tony Blake

Intellectual 600 points

The noisy signal shown previously is due to a bad scope channel. I've changed the scope channel and am now getting a 3.3 V signal on the I2C lines. As you can see, no pulses are present:

Also, the fact that both SCL and SDA are both high would suggest that the I2C start condition is not occurring:

0 YiKai Chen over 8 years ago in reply to Tony Blake

Guru 735685 points

Can you show me how you initialize I2C and do I2C transfer in your application?

0 Tony Blake over 8 years ago in reply to YiKai Chen

Intellectual 600 points

It's a sample project so I have not changed any code:

if (SensorMpu9250_init())
{
SensorTagMov_reset();
SensorMpu9250_registerCallback(SensorTagMov_processInterrupt);
}

0 Tony Blake over 8 years ago in reply to Tony Blake

Intellectual 600 points

The slave address is set to 0xFF. This this correct? If so, why?

0 Tony Blake over 8 years ago in reply to Tony Blake

Intellectual 600 points

According to the MPU9250 datasheet, the I2C address is 1101000 (0x68) with pin AD0 pulled to GND or 1101001 (0x69) with AD0 pulled high to 3.3 V.

I've set the slave address to 0x68 and connected AD0 to GND but still no joy...

0 YiKai Chen over 8 years ago in reply to Tony Blake

Guru 735685 points

In SensorTag example, it defines "#define SENSOR_SELECT() SensorI2C_select(SENSOR_I2C_1,Board_MPU9250_ADDR)" to use SENSOR_I2C_1. Since you don't use I2C_1, do you change it to SENSOR_I2C_0?

0 Tony Blake over 8 years ago in reply to YiKai Chen

Intellectual 600 points

Hi Yikai,

That was the problem. I just changed SENSOR_I2C_1 to SENSOR_I2C_0 and the WHO_AM_I register is now returning 0x71 as it should.

Thank you very much for your help.

Tony

0 YiKai Chen over 8 years ago in reply to Tony Blake

Guru 735685 points

You are welcome and it's good to know that works.

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LAUNCHXL-CC2650: MPU9250 not initializing