FXLS8471Q datasheet(60/75 Pages) FREESCALE

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FXLS8471Q

Sensors

Freescale Semiconductor, Inc.

10.10.3 TRANSIENT_THS (0x1F) register

The TRANSIENT_THS register determines the debounce counter behavior and also sets the transient event detection

threshold.It is possible to use A_FFMT_THS_X/Y/Z MSB and LSB registers to set transient acceleration thresholds for individual

axes using the a_ffmt_trans_ths_en bit in A_FFMT_THS_Y_MSB register.

The tr_ths[6:0] value is a 7-bit unsigned number, with a fixed resolution of 63 mg/LSB corresponding to a ±8 g measurement

range. The resolution does not change with the full-scale range setting made in XYZ_DATA_CFG[fs]. If CTRL_REG1[lnoise] = 1,

the measurement range is fixed at ±4 g, regardless of the settings made in XYZ_DATA_CFG.

10.10.4 TRANSIENT_COUNT (0x20) register

The TRANSIENT_COUNT register sets the minimum number of debounce counts needed to trigger the transient event interrupt

flag when the measured acceleration value exceeds the threshold set in TRANSIENT_THS for any of the enabled axes.

The time step for the transient detection debounce counter is set by the value of the system ODR and power mode as shown in

Table 117.

An ODR of 100 Hz and a TRANSIENT_COUNT value of 15, when accelerometer OSR is set to normal using CTRL_REG2,

would result in minimum debounce response time of 150 ms.

Table 113. TRANSIENT_THS register

tr_dbcntm

tr_ths[6:0]

7’b0000000

Table 114. TRANSIENT_THS bit descriptions

Field

Description

tr_dbcntm

Debounce counter mode selection.

0: Decrements debounce counter when the transient event condition is not true during the current ODR period.

1: Clears debounce counter when the transient event condition is not true during the current ODR period.

tr_ths[6:0]

Transient event threshold. This register has a resolution of 63 mg/LSB regardless of the full-scale range setting made in

XYZ_DATA_CFG[fs]. If CTRL_REG1[lnoise] = 1, the maximum acceleration measurement range is ±4 g.

Table 115. TRANSIENT_COUNT register

tr_count[7:0]

8’b00000000

Table 116. TRANSIENT_COUNT bit description

Field

Description

tr_count[7:0)

Transient function debounce count value.

Table 117. TRANSIENT_COUNT relationship with the ODR

ODR (Hz)

Max time range (s)

Time step (ms)

Normal

LPLN

High

resolution

Low power

Normal

LPLN

High

resolution

Low power

800

0.319

1.25

400

0.638

2.5

200

1.28

0.638

1.28

2.5

100

2.55

0.638

2.55

2.5

5.1

0.638

5.1

2.5

12.5

5.1

20.4

0.638

20.4

2.5

6.25

5.1

20.4

0.638

40.8

2.5

160

1.56

5.1

20.4

0.638

40.8

2.5

160

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