AN4504 datasheet(24/41 Pages) STMICROELECTRONICS

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Interrupt generation

AN4504

24/41

DocID026419 Rev 1

5.5.2

HP filter bypassed

This paragraph provides a basic algorithm which shows the practical use of the wake-up

feature. In particular, with the code below, the device is configured to recognize when the

absolute angular rate along either the X-, Y-, or Z-axis exceeds a preset threshold (100 dps

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.

5.5.3

Using the HP filter

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

up feature performed on high-pass filtered data. In particular the device is configured to

recognize when the high-frequency component of the angular rate applied along either the

X-, Y-, or Z-axis exceeds a preset threshold (100 dps 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.

Write 0Fh 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 80h into CTRL_REG3

// Interrupt driven to INT1 pad

Write 00h into CTRL_REG4

// FS = 250 dps

Write 2Ch into INT1_THS_XH

// Threshold = 100 dps

Write A4h into INT1_THS_XL

// Threshold = 100 dps

Write 00h into INT1_DURATION

// Duration = 0

Write 02h into INT1_CFG

// Enable XH interrupt generation

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

// Poll INT1 pin waiting for the

// wake-up event

10 Read INT1_SRC

// Return the event that has triggered the

// interrupt

(Wake-up event has occurred; insert

your code here)

// Event handling

12 Go to 8

Write 0Fh into CTRL_REG1

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

// ODR = 100 Hz

Write 00h into CTRL_REG2

// High-pass filter in normal mode

Write 80h into CTRL_REG3

// Interrupt driven to INT1 pad

Write 00h into CTRL_REG4

// FS = 250 dps

Write 05h into CTRL_REG5

// Data in DataReg and FIFO are high-pass filtered

// High-pass-filtered data are used for interrupt

// generation

Write 2Ch into INT1_THS_XH

// Threshold = 100 dps

Write A4h into INT1_THS_XL

// Threshold = 100 dps

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