What is the SPI mode of the gyroscope sensor I3G4250D?

[duoc_ngo261]

I use the KIT STM32F411 Discovery

When I choose:

SPI CPOL: Low

SPI CPHA: 1 Edge

It works

But when I choose:

SPI CPOL: High

SPI CPHA: 2 Edge

It does not work

Could you explain why? Thank you!

[TDK]

> SPI CPOL: High

> SPI CPHA: 2 Edge

These are the correct settings. If it doesn't work, there's probably a bug in your code.

Ensure SPI peripheral is active before you assert CS. Send a dummy transfer without CS active in order to ensure this.

[duoc_ngo261]

This is my main.c file. It's short

Could you help me review a little bit? Thank you very much

[TDK]

What about your program isn't working?

What does L3GD20_Read_WHOAMI return?

> hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;
> hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;

These are incorrect, as explained above.

[duoc_ngo261]

I recorded my screen and send you my project in the attachment.

It works when:

 > hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;
> hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;

It does not work when:

 > hspi1.Init.CLKPolarity = SPI_POLARITY_HIGH;
> hspi1.Init.CLKPhase = SPI_PHASE_2EDGE;

I still don't know why : ((

Thank you very much !!!

[TDK]

If you can't clearly explain what isn't working here, I'm afraid I won't be able to help. I'm not watching a 4.5 minute video to try and find out. You didn't answer my question about L3GD20_Read_WHOAMI.

[duoc_ngo261]

Hi

What does L3GD20_Read_WHOAMI return?

--> It returns 211

When I use 

 > hspi1.Init.CLKPolarity = SPI_POLARITY_HIGH;
> hspi1.Init.CLKPhase = SPI_PHASE_2EDGE;

The sensor returns only 1 time (then the sensor data does not change anymore)

Do you know the reason why?

Thank you

[TDK · Accepted solution]

Try doing a dummy SPI transfer (with CS high) prior to your first SPI transaction, but after SPI is initialized.

If that doesn't work, please include the code you're using with the fixes from above.

[duoc_ngo261]

"Try doing a dummy SPI transfer (with CS high) prior to your first SPI transaction, but after SPI is initialized."

-->Wowww. It works. Thank you very much. Could you explain why?

[TDK]

The CLK pin is not driven until the peripheral is enabled. On the first transaction, it's low when you set CS low, which messes up the first transfer. Doing a dummy transfer enables the peripheral. See my first reply.