FXLS8471Q Datasheet, PDF (60/75 Pages) Freescale Semiconductor, Inc – Linear Accelerometer

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.
Table 113. TRANSIENT_THS register
tr_dbcntm
0
tr_ths[6:0]
7’b0000000
Table 114. TRANSIENT_THS bit descriptions
Field
tr_dbcntm
tr_ths[6:0]
Description
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.
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.
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.
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.
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.
Table 117. TRANSIENT_COUNT relationship with the ODR
ODR (Hz)
800
400
200
100
50
12.5
6.25
1.56
Normal
0.319
0.638
1.28
2.55
5.1
5.1
5.1
5.1
Max time range (s)
LPLN
High
resolution
0.319
0.319
0.638
0.638
1.28
0.638
2.55
0.638
5.1
0.638
20.4
0.638
20.4
0.638
20.4
0.638
Low power
0.319
0.638
1.28
2.55
5.1
20.4
40.8
40.8
Normal
1.25
2.5
5
10
20
20
20
20
Time step (ms)
LPLN
High
resolution
1.25
1.25
2.5
2.5
5
2.5
10
2.5
20
2.5
80
2.5
80
2.5
80
2.5
Low power
1.25
2.5
5
10
20
80
160
160
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.
FXLS8471Q
60
Sensors
Freescale Semiconductor, Inc.