AN2960 Datasheet, PDF(35/41 Page) STMicroelectronics – ultra compact linear accelerometer

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AN2960 Datasheet, PDF (35/41 Pages) STMicroelectronics – ultra compact linear accelerometer

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AN2960

Application information

The FF_WU_CFG(LIR) bit permits the determination of whether or not the interrupt request

should be latched. If the LIR bit is â0â (default value), the interrupt signal goes high when the

interrupt condition is satisfied and comes back low immediately if the interrupt condition is

no longer verified. Otherwise, if the LIR bit is â1â, whenever an interrupt condition is applied

the interrupt signal remains high even if the condition returns to a non-interrupt status, until

a reading to the FF_WU_SRC register is performed.

The remaining bits of the FF_WU_CFG register allow the decision as to which axis the

interrupt should be performed on and in which direction the threshold must be exceeded to

generate the interrupt request.

9.5

9.5.1

Inertial wake-up

HP filter bypassed

This paragraph provides a basic algorithm which shows the practical use of the inertial

wake-up feature. In particular, with the code below, the device is configured to recognize

when the absolute acceleration along either X or Y axis exceeds a preset threshold (180 mg

is used in the example). The event which triggers the interrupt is latched inside the device

using FF_WU interrupt source 1 and its occurrence is signalled through the use of the INT2

pin.

1 write C7h into CTRL_REG1

// Turn-on the sensor and set ODR=400Hz

2 write 00h into CTRL_REG2

// Default value: high-pass filter bypassed

3 write 08h into CTRL_REG3

// FF_WU1 interrupt sent to INT2 pin

4 write 0Ah into FF_WU_THS_1 reg

// Set wake-up threshold = 180 mg

5 write 00h into FF_WU_DURATION_1 reg

// No filtering/confirmation on the event

6 write 4Ah into FF_WU_CFG_1

// Configure desired wake-up event

7 poll INT2 pin; if INT2=0 then goto 7

// Poll INT2 pin waiting for the wake-up event

8 read FF_WU_SRC_1 reg

// Return the event that has triggered the

interrupt

// Clear interrupt request

(Wake-up event has occurred; insert your code

here)

// Event handling

10 goto 7

Doc ID 15557 Rev 1

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