AN4504 datasheet(25/41 Pages) STMICROELECTRONICS

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AN4504

Interrupt generation

At step 13, a dummy read of the REFERENCE register is performed to set the

current/reference angular rate/tilt state against which the device performed the threshold

comparison.

This read may be performed any time it is required to set the current rate as a reference

state without waiting for the filter to settle.

5.6

Selective axis movement detection

Selective axis movement detection refers to a specific configuration of the INT1_CFG and

INT1_THS registers that allows recognizing when the device is rotating only around the

selected axis.

Referring to Figure 12, a “no rotation zone” is defined around the zero-dps level where the

angular rates are small enough to be considered as zero. It is possible to create a

configuration of the INT1_CFG register so that an interrupt is generated only if, i.e., the

angular rates for the rotation around the X and Y axes are around zero while it is different

from zero for the Z-axis. This means the device is doing a pure yaw rotation.

Write 2Ch into INT1_THS_YH

// Threshold = 100 dps

Write A4h into INT1_THS_YL

// Threshold = 100 dps

10 Write 2Ch into INT1_THS_ZH

// Threshold = 100 dps

Write A4h into INT1_THS_ZL

// Threshold = 100 dps

12 Write 00h into INT1_DURATION

// Duration = 0

13 Read REFERENCE

// Dummy read to force the HP filter to

// current angular rate value

// (i.e. set reference angular rate)

14 Write 6Ah into INT1_CFG

// Enable XH, YH and ZH interrupt generation

// Interrupt latched

15 Poll INT1 pad; if INT1=0 then go to 8

// Poll INT1 pin waiting for the

// wake-up event

16 Read INT1_SRC

// Return the event that has triggered the

// interrupt

(Wake-up event has occurred; insert

your code here)

// Event handling

18 Go to 15

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