FXLS8471Q Datasheet, PDF (53/75 Pages) Freescale Semiconductor, Inc – Linear Accelerometer

Table 85. A_FFMT_THS_Z_MSB (0x77) register
—
0
Table 86. A_FFMT_THS_Z_LSB (0x78) register
a_ffmt_ths_z[5:0]
6’b000000
a_ffmt_ths_z[12:6]
7’b0000000
—
—
0
0
X, Y, Z High-g Region
X, Y, Z Low-g Region
X, Y, Z High-g Region
+Full Scale
High-g Positive Threshold
(Motion OR of enabled axes)
Low-g Threshold
(Freefall - AND of enabled axes)
High-g Negative Threshold
(Motion - OR of enabled axes)
-Full Scale
Positive
Acceleration
Negative
Acceleration
Figure 16. A_FFMT_THS high and low-g level
A_FFMT_THS contains the unsigned 7-bit threshold value used by the freefall/motion detection functional block and is used to
detect either low-g (freefall) or high-g (motion) events depending on the setting of G_FFMT_CFG[f_ffmt_oae]. If g_ffmt_oae = 0,
the event is detected when the absolute value of all the enabled axes are below the threshold value. When g_ffmt_oae = 1, the
event is detected when the absolute value of any of the enabled axes is above the threshold value (see Figure 16 for an
illustration of the freefall/motion event detection thresholds). If A_FFMT_THS_X_MSB[a_ffmt_ths_xyz_en] = 1, the behavior is
identical, except that each axis may be programmed with an individual 13-bit threshold (stored in the A_FFMT_X/Y/Z MSB and
LSB registers).
10.8.4 A_FFMT_COUNT (0x18) register
Debounce count register for freefall/motion detection events
This register sets the number of debounce counts for acceleration sample data matching the user-programmed conditions for
either a freefall or motion detection event required before the interrupt is triggered.
Table 87. A_FFMT_COUNT register
a_ffmt_count[7:0]
8’b00000000
Table 88. A_FFMT_COUNT bit description
Field
a_ffmt_count[7:0]
Description
a_ffmt_count defines the minimum number of debounce sample counts required for the detection of a freefall or motion
event. A_FFMT_THS[ffmt_dbcntm] determines the behavior of the counter when the condition of interest is momentarily
not true.
When the internal debounce counter reaches the A_FFMT_COUNT value a freefall/motion event flag is set. The debounce
counter will never increase beyond the A_FFMT_COUNT value. The time step used for the debounce sample count depends on
the ODR chosen (see Table 89).
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FXLS8471Q
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