Interrupt generation

AN2989

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Doc ID 15761 Rev 1

5.4

Inertial wakeup

The wakeup 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 wakeup interrupt

5.4.1

HP filter bypassed

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

wakeup 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 use of the INT1 pin.

1

write 2Fh into CTRL_REG1

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

// ODR = 100 Hz

2

write 00h into CTRL_REG2

// High-pass filter disabled

3

write 00h into CTRL_REG3

// Latched interrupt active high on INT1 pad

4

write 00h into CTRL_REG4

// FS = 2g

5

write 00h into CTRL_REG5

// Sleep to wake disabled

6

write10h into INT1_THS

// Threshold = 250 mg

7

write 00h into INT1_DURATION

// Duration = 0

8

write 0Ah into INT1_CFG

// Enable XH and YH interrupt generation

9

poll INT1 pad; if INT1=0 then goto 8

// Poll RDY/INT pin waiting for the

// wakeup event

10

read INT1_SRC

// Return the event that has triggered the

// interrupt

11

(Wakeup event has occurred; insert your

code here)

// Event handling

12

goto 8