AN3308 datasheet(23/52 Pages) STMICROELECTRONICS

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AN3308

Inertial interrupt

Doc ID 18198 Rev 1

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6.3.1

Inertial wake-up

Wake-up interrupt refers to a specific configuration of the INT1_CTRL register that allows

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

threshold (Figure 9).

Figure 9.

Inertial wake-up interrupt

6.3.2

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 the 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 signalled through the use of the INT1 pin.

Write A7h 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 40h into CTRL_REG3

// Interrupt driven to INT1 pad

Write 00h into CTRL_REG4

// FS = 2 g

Write 08h into CTRL_REG5

// Interrupt latched

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 go to 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

Go to 8

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