FXOS8700CQ datasheet(50/86 Pages) FREESCALE

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Sensors

Freescale Semiconductor, Inc.

Figure 53. 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 53 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).

9.9.4

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.

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 53). When the device is operated in hybrid mode, the effective ODR is half of what is selected in

CTRL_REG1. This has the effect of doubling the time-step values shown in Table 53.

a_ffmt_ths_z[5:0]

—

0b000000

Figure 52. A_FFMT_THS_Z_LSB (0x78) register

a_ffmt_count[7:0]

0b00000000

Figure 54. A_FFMT_COUNT register

Table 53. A_FFMT_COUNT bit description

Field

Description

a_ffmt_count[7:0]

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.

+Full Scale

High-g Positive Threshold

Low-g Threshold

High-g Negative Threshold

-Full Scale

X, Y, Z High-g Region

X, Y, Z Low-g Region

Negative

Positive

Acceleration

(Motion OR of enabled axes)

(Freefall - AND of enabled axes)

(Motion - OR of enabled axes)

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