AN2960 datasheet(37/41 Pages) STMICROELECTRONICS

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AN2960

Application information

Doc ID 15557 Rev 1

37/41

9.6

Free-fall detection

9.6.1

Roll function not used

This paragraph provides the basics for the use of the free-fall detection feature. The SW

routine that configures the device to detect free-fall events and to signal them is as follows:

The code sample exploits a threshold set at 350 mg for free-fall recognition and the event is

notified by the hardware signal INT2 pin. At step 5, the FF_WU_DURATION_1 register is

configured to ignore events that are shorter than 9/ODR=9/100~90 ms (ODR=output data

rate) in order to avoid false detections.

Once the free-fall event has occurred, a dummy read at FF_WU_SRC_1 reg clears the

request and the device is ready to recognize other events.

9.6.2

Roll function applied

The roll function can be added to free-fall condition recognition using both interrupt sources.

Interrupt signals can be sent to two different pins (INT1, INT2) or can be sent to the same

pin so that the first condition verified controls the pin (logic “OR” of interrupt signals).

9.7

Output data rate selection and reading timing

The output data rate is user-selectable through the DR bit stored in the CTRL_REG1 (20h)

100 Hz.

The selectable output data rates are given in Table 6 below:

write 47h into CTRL_REG1

// Turn-on the sensor and set ODR=100 Hz

write 00h into CTRL_REG2

// Default value: high-pass filter bypassed

write 08h into CTRL_REG3

// FF_WU1 interrupt sent to INT2 pin

write 14h into FF_WU_THS_1 reg

// Set the free-fall threshold

write 09h into FF_WU_DURATION_1 reg

// Set minimum event duration to 90 ms

write D5h into FF_WU_CFG_1

// Configure free-fall recognition and latch

// interrupt request

poll INT2 pad; if INT2=0 then goto 7

// Poll INT2 pin waiting for the free-fall event

(Free-fall event has occurred; insert your code

here)

// Event handling

read FF_WU_SRC_1 register

// Clear interrupt request

goto 7

Table 6.

Output data rate

100 Hz

400 Hz

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