AN2381 datasheet(41/47 Pages) STMICROELECTRONICS

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AN2381

Application information

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6.5

Inertial wake-up

6.5.1

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 (100mg

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

its occurrence is signalled through the usage of the RDY/INT pin.

6.5.2

Using the HP filter

The code provided below gives a basic routine which shows the practical use of the inertial

wake-up feature performed onto high-pass filtered data. In particular the device is

configured to recognize when the high-frequency component of the acceleration applied

along either X, Y or Z axis exceeds a preset threshold (100mg used in the example). The

event which triggers the interrupt is latched inside the device and its occurrence is signalled

through the usage of the RDY/INT pin.

write C7h into CTRL_REG1

// Turn on the sensor and set DF=512

write 08h into CTRL_REG2

// Enables interrupt generation

write 08h into CTRL_REG3

// Set CTRL_REG3 to its default state

write 60h into FF_WU_THS_L register

// Set the lower part of wake-up threshold

write 06h into FF_WU_THS_H register

// Set the higher part of wake-up threshold

write 00h into FF_WU_DURATION

// No filtering/confirmation on the event

write 4Ah into FF_WU_CFG

// Configure desired wake-up event

poll RDY/INT pad; if RDY/INT=0 then

goto 8

// Poll RDY/INT pin waiting for the

// wake-up event

read FF_WU_SRC register

// Return the event that has triggered the

// interrupt

(Wake-up event has occurred; insert

your code here)

// Event handling

read FF_WU_ACK register

// Clear interrupt request

goto 8

write C7h into CTRL_REG1

// Turn on the sensor and set DF=512

write 08h into CTRL_REG2

// Enables interrupt generation

write 28h into CTRL_REG3

// Enable the HP filter and force HPc=512

write 60h into FF_WU_THS_L register

// Set the lower part of wake-up threshold

write 06h into FF_WU_THS_H register

// Set the higher part of wake-up threshold

write 00h into FF_WU_DURATION

// No filtering/confirmation on the event

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