Sensors中的主题 Accelerometer FXOS8700CQ

Accelerometer FXOS8700CQ

joãopaulo — Tue, 03 Feb 2026 22:35:24 GMT

I am not able to use the FXOS8700CQ accelerometer present on the kv31f board.
I would like to use the freefall function and for this I configured the following registers.

Freefall Configuration			Z < 0,3g using MFF Function 4g, 100 Hz ODR, Normal Mode
Register Name	Register Addr	Data (R/W)	Description
CTRL_REG1	0x2A	0x00 W	Standby mode for writable operations
WHO_AM_I	0x0D	Read	Check device communication (0xC7)
XYZ_DATA_CFG	0x0E	0x01 W	Hight-pass filter disabled, +/-0.488mg/LSB
CTRL_REG1	0x2A	0x18 W	Set the device in 100 Hz ODR, Standby
A_FFMT_CFG	0x15	0xA0 W	Latch enable, Freefall, Z axis
A_FFMT_THS	0x17	0x05 W	0,3g threshold
A_FFMT_COUNT	0x18	0x0A W	Debounce 100ms
CTRL_REG4	0x2D	0x04 W	FF interrupt enable
CTRL_REG5	0x2E	0x04 W	interrupt routed to INT1 pin
CTRL_REG1	0x2A	0x19 W	Set the device in 100 Hz ODR, Active Mode

- The communication is working properly because I can read the WHO_AM_I register,

- I've already followed the AN4070 document,

But it's not working, the Freefall interrupt isn't happening,

I've tried to use the 3 axes and then only one but none worked.

Is there any other register that I need to configure?

What else should I do?

Thanks

Re: Accelerometer FXOS8700CQ

david_diaz — Wed, 23 Aug 2017 17:54:34 GMT

Hello Paulo,

Your configuration seems correct.

Please make sure you have the correct pin configuration using the FRDM-KV31F as mentioned below, especially the INT1 pin:

Please try to decrease the value of the debounce counter (A_FFMT_COUNT = 0x01). Can you share your results? Is the interrupt generated at the PTD0 pin?

Regards,

David

Re: Accelerometer FXOS8700CQ

joãopaulo — Wed, 23 Aug 2017 19:00:59 GMT

Hello,

There was a mistake on I2C write messages,

So I could read the Who_Am_I but when I was trying to write to registers it was working..

In the end the configuration that I did was:

Register Name	Register Addr	Data (R/W)
CTRL_REG2	0x2B	0x40 W	Reset all registers to POR values
XYZ_DATA_CFG	0x0E	0x00 W	Hight-pass filter disabled, +/-0.244mg/LSB, Full-Scale range +/-2g
M_CTRL_REG	0x5B	0x00 W	Only accelerometer sensor is active
CTRL_REG2	0x2B	0x02 W	High Resolution mode
CTRL_REG3	0x2C	0x00 W	Push-pull, active low interrupt
A_FFMT_CFG	0x15	0x08 W	Freefall detection for X axis
A_FFMT_THS	0x17	0x04 W	Threshold Setting Value for the Freefall detection of 0.2g (4 * 0.063)
A_FFMT_COUNT	0x18	0x0A W	Set the debounce counter to 1,6s timer (160ms * 10)
CTRL_REG4	0x2D	0x04 W	FF interrupt enable
CTRL_REG5	0x2E	0x04 W	interrupt routed to INT1 pin
CTRL_REG1	0x2A	0x35 W	ODR = 6.25Hz, Reduced noise, Active mode

Thanks,

Best Regards,

João Paulo