Can't start MMA6900 accelerometer

[voronin_mikhail]

Hi,

I'm using MMA6900KQ accelerometer and can't read acceleration data. I'm using SPI to read it. 

First I'm trying to init accelerometer. Here commands which I send via SPI and answers on it:

1) MOSI: 0x1410;      MISO: 0xEA00;   (Command: Set pointer to Device Status Register; answer:  Critical/Reset Exception Response)

2) MOSI: 0x2000;      MISO: 0xF281;   (Command: DEVSTAT register data read; answer: 2 errors (IDE and DEVRES)

3) MOSI: 0x140E;      MISO: 0xEA00;   (Command: Set pointer to DEVCTL register; answer: Critical/Reset Exception Response)

4) MOSI: 0x3020;      MISO: 0xFA0E;   (Command: Register data write, data: Clear Error; answer: Critical/Reset Exception Response)

5) MOSI: 0x1410;      MISO: 0xEA00;   (Command: Set pointer to Device Status Register; answer:  Critical/Reset Exception Response)

6) MOSI: 0x2000;      MISO: 0xF680;   (Command: DEVSTAT register data read; answer: 1 error (IDE)

And after it I'm trying to read acceleration data. As answer I've got 0x2047 acceleration always. 

Help me, please, how to deal with this problem?

[voronin_mikhail]

Thank you very much, Tomas! It helped me!

[TomasVaverka · Accepted solution]

Hi Mikhail,

The sequence for clearing errors looks correct, but we recommend using the soft reset sequence immediately after a power on to prevent issues due with the OTP readout after a power on.

Could you try the sequence below? 

MOSI     Expected MISO

0x1410  0xEA00

0x2000  0xF601

0x140E  0xEA00 // Set CE bit

0x3020  0xFA0E

0x1410  0x0800  // Read DEVSTAT

0x2000  0x1000

0x140E  0x0800  // Soft Reset

0x3080  0x180E

0x34C0  0x180E

0x3040  0x180E

// Delay 5ms Minimum

0x1410  0xEA00 

0x2000  0xF601

0x140E  0xEA00 // Set CE bit

0x3020  0xFA0E

0x1410  0x0800  // Read DEVSTAT

0x2000  0x1000

0x4000  0x3806  // Read X-Axis

0x8000  0x4802  // Read Y-Axis

0x4000  0x380C

0x8000  0x47FE

0x4000  0x280E

0x8000  0x57FC

0x4000  0x280E

0x8000  0x47FE

0x4000  0x280E

0x8000  0x57FC

I hope it helps!

Best regards,

Tomas