MMA8451Q_12 datasheet(36/52 Pages) FREESCALE

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MMA8451Q

Sensors

Freescale Semiconductor, Inc.

0x1F: TRANSIENT_THS Register

The Transient Threshold register sets the threshold limit for the detection of the transient acceleration. The value in the

TRANSIENT_THS register corresponds to a g value which is compared against the values of High-Pass Filtered Data. If the High-

Pass Filtered acceleration value exceeds the threshold limit an event flag is raised and the interrupt is generated if enabled.

The threshold THS[6:0] is a 7-bit unsigned number, 0.063g/LSB. The maximum threshold is 8g. Even if the part is set to full

scale at 2g or 4g this function will still operate up to 8g. If the Low Noise bit is set in Register 0x2A the maximum threshold to be

reached is 4g.

0x20: TRANSIENT_COUNT

The TRANSIENT_COUNT sets the minimum number of debounce counts continuously matching the condition where the

unsigned value of high-pass filtered data is greater than the user specified value of TRANSIENT_THS.

The time step for the transient detection debounce counter is set by the value of the system ODR and the Oversampling mode.

0x1F: TRANSIENT_THS Register (Read/Write)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

DBCNTM

THS6

THS5

THS4

THS3

THS2

THS1

THS0

Table 41. TRANSIENT_THS Description

DBCNTM

Debounce counter mode selection. Default value: 0. 0: increments or decrements debounce; 1: increments or clears counter.

THS[6:0]

Transient Threshold: Default value: 000_0000.

0x20: TRANSIENT_COUNT Register (Read/Write)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Table 42. TRANSIENT_COUNT Description

D[7:0]

Count value. Default value: 0000_0000.

Table 43. TRANSIENT_COUNT Relationship with the ODR

ODR (Hz)

Max Time Range (s)

Time Step (ms)

Normal

LPLN

HighRes

Normal

LPLN

HighRes

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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