CMA3000-D0X Datasheet, PDF (10/35 Pages) VTI technologies – 3-axis accelerometer

CMA3000-D0X Series
2.4.3 Example
Below is a simple example of motion detection usage:
1. Write "00001000" (08h) into the MODE register (enable motion detection mode, MODE[2:0]
bits = '100').
2. Band pass filtered acceleration data at 10 Hz sample rate is available at the output
registers.
3. The INT-pin is activated when motion is detected; see section 2.6 for detailed INT-pin
information.
2.5 Free-Fall Detection
2.5.1 Description
During free-fall in the gravitation field, all 3 orthogonal acceleration components are ideally equal to
zero. Due to practical non-idealities, detection must be done using Threshold Level (TL) greater
than 0.
When enabled, the Free-Fall Detection (FFD) will monitor the measured acceleration in the X, Y
and Z directions. If all measured XYZ acceleration values stay within the TL longer than time TFF
(Figure 5 below), the FFD will generate an interrupt to the INT-pin. TL can be controlled by FFTHR
[6:0] and TFF by FFTMR [3:0] bits.
Acceleration
X, Y and Z
+TL
T1
T2
T3
T4
T5
T6
T7
T8 Time
-TL
INT output
TFF
"1"
"0"
T1
T2
T3
T4
T5
T6
T7
T8 Time
Figure 5. Free Fall condition
2.5.2 Usage
Free-fall detection can be enabled by setting MODE[2:0] bits in the CTRL register to "101" (sample
rate 100 Hz) or to "110" (sample rate 400 Hz). See section 3.3 for MODE register details.
Acceleration data is available in registers DOUTX, DOUTY and DOUTZ as in measurement mode.
See section 3.3 for output register and section 2.6 for interrupt functionality details.
2.5.3 Example
Below is a simple example of free-fall detection usage:
1. Write "00001100" (0Ch) into the MODE register (enable 400 Hz free fall detection mode,
MODE[2:0] bits = '110').
2. Acceleration data can be read normally
3. INT-pin is activated when free fall is detected. See section 2.6 for detailed INT-pin
information.
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