AN2847 datasheet(24/31 Pages) STMICROELECTRONICS

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Interrupt generation

AN2847

24/31

Doc ID 15136 Rev 2

5.4

Inertial wake-up

The wake-up interrupt refers to a specific configuration of the INTx_CTRL registers that

allow the interrupt generation when the acceleration on the configured axis exceeds a

defined threshold (

Figure 10).

Figure 10.

Inertial wake-up interrupt

5.4.1

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 (250 mg

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

its occurrence is signaled through the usage of the INT1 pin.

0 g

WAKE UP

THRESHOLD

WKP Interrupt

0 g

WAKE UP

THRESHOLD

WKP Interrupt

WU Interrupt

write 2Fh into CTRL_REG1

// Turn on the sensor and enable X, Y and Z

// ODR = 100 Hz

write 00h into CTRL_REG2

// High pass filter disabled

write 00h into CTRL_REG3

// Latched interrupt active high on INT1 pad

write 00h into CTRL_REG4

// FS = 2 g

write 00h into CTRL_REG5

// Sleep to Wake disabled

write10h into INT1_THS

// Threshold = 250 mg

write 00h into INT1_DURATION

// Duration = 0

write 0Ah into INT1_CFG

// Enable XH and YH interrupt generation

poll INT1 pad; if INT1=0 then goto 8

// Poll RDY/INT pin waiting for the

// wake-up event

read INT1_SRC

// Return the event that has triggered the

// interrupt

(Wake-up event has occurred; insert

your code here)

// Event handling

goto 8

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