AN4650 datasheet(48/102 Pages) STMICROELECTRONICS

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Interrupt generation

AN4650

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DocID027415 Rev 1

4.5.5

Double-tap example

The example code which implements the SW routine for single-tap detection is given below.

In this example the TAP_THS field of the TAP_THS_6D register is set to 01100b, therefore

the tap threshold is 750 mg (= 12 * FS_XL / 25).

For interrupt generation, during the first and the second tap the slope data must return

below the threshold before the Shock window has expired. THe SHOCK field of the

INT_DUR2 register is set to 11b, therefore the Shock time is 57.7 ms (= 3 * 8 / ODR_XL).

For interrupt generation, after the first tap recognition there must not be any slope data

overthreshold during the Quiet time window. Furthermore, since the latch mode is disabled,

the interrupt is kept high for the duration of the Quiet window. The QUIET field of the

INT_DUR2 register is set to 11b, therefore the Quiet time is 28.8 ms (= 3 * 4/ ODR_XL).

For the maximum time between two consecutive detected taps, the DUR field of the

INT_DUR2 register is set to 0111b, therefore the Duration time is 538.5 ms (= 7 * 32 /

ODR_XL).

4.6

Activity/Inactivity recognition

The Activity/Inactivity recognition function allows reducing system power consumption and

developing new smart applications.

When the Activity/Inactivity recognition function is activated, the LSM6DS3 device is able to

automatically decrease the accelerometer sampling rate to 13 Hz, increasing the

accelerometer ODR and bandwidth as soon as the wake-up interrupt event has been

detected. This feature is applied to the accelerometer sensor only, regardless of the

selected gyroscope power mode and ODR.

With this feature the system may be efficiently switched from low-power consumption to full

performance and vice-versa depending on user-selectable acceleration events, thus

ensuring power saving and flexibility.

The Activity/Inactivity recognition function is enabled by setting to 1 the INACTIVITY bit of

the WAKE_UP_THS register.

The Activity/Inactivity recognition function uses the slope between two consecutive

acceleration samples to detect the Activity/Inactivity event; the slope data is computed using

the following formula:

slope(tn) = [ acc(tn) - acc(tn-1) ] / 2

Write 60h into CTRL1_XL

// Turn on the accelerometer

// ODR_XL = 416 Hz, FS_XL = 2g

Write 0Eh into TAP_CFG

// Enable tap detection on X, Y, Z axis

Write 0Ch into TAP_THS_6D

// Set tap threshold

Write 7Fh into INT_DUR2

// Set Duration, Quiet and Shock time windows

Write 80h into WAKE_UP_THS

// Single & Double tap enabled (SINGLE_DOUBLE_TAP = 1)

Write 08h into MD1_CFG

// Double tap interrupt driven to INT1 pin

AN4650 Datasheet(PDF) 48 Page - STMicroelectronics

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