AN2335 datasheet(34/40 Pages) STMICROELECTRONICS

34 / 40 page

Application Information

AN2335

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FF_WU_CFG(LIR) bit permits to decide if the interrupt request has to be latched or not. If

LIR bit is ‘0’ (default value) interrupt signal goes high when the interrupt condition is satisfied

and comes back low immediately if the interrupt condition is no more verified. Otherwise if

LIR bit is ‘1’ whenever a interrupt condition is applied the interrupt signal remains high even

if the condition comes back to non-interrupt status until a reading to FF_WU_SRC register is

performed.

The remaining bits of FF_WU_CFG register permits to decide on which axis the interrupt

decision has to be performed and on which direction the threshold has to be passed to

generate the interrupt request.

9.5

INERTIAL WAKE-UP

9.5.1

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 (180mg

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 usage of the

INT2 pin.

write C7h into CTRL_REG1

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

write 00h into CTRL_REG2

// Default value: High Pass filter bypassed

write 08h into CTRL_REG3

// FF_WU1 interrupt sent to INT2 pin

write 0Ah into FF_WU_THS_1 reg

// Set wake-up threshold = 180 mg

write 00h into FF_WU_DURATION_1 reg

// No filtering/confirmation on the event

write 4Ah into FF_WU_CFG_1

// Configure desired wake-up event

poll INT2 pin; if INT2=0 then goto 7

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

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

goto 7

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