MMA8450QT datasheet(37/57 Pages) FREESCALE

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Sensors

Freescale Semiconductor

MMA8450Q

0x31 - 0x33: PULSE_THSX, Y, Z Pulse Threshold for X, Y & Z Registers

The pulse threshold can be set separately for the X, Y and Z axes. The threshold values range from 0 to 31 counts with steps

of 0.258g/LSB at a fixed 8g acceleration range, thus the minimum resolution is always fixed at 0.258g/LSB irrespective of the

selected g range.

The PULSE_THSX, PULSE_THSY and PULSE_THSZ registers define the threshold which is used by the system to start the

pulse detection procedure. The threshold value is expressed over 5-bits as an unsigned number.

0x34: PULSE_TMLT Pulse Time Window 1 Register

The bits Tmlt7 through Tmlt0 define the maximum time interval that can elapse between the start of the acceleration on the

selected axis exceeding the specified threshold and the end when the acceleration on the selected axis must go below the

specified threshold to be considered a valid pulse.

The minimum time step for the pulse time limit is defined in Table 48. Maximum time for a given ODR is the minimum time step

at the given power mode multiplied by 255. The time steps available are dependent on whether the device is in Normal Power

mode or in Low Power mode. Notice in the table below that the time step is twice as long in Low Power mode.

Therefore an ODR setting of 400 Hz with normal power mode would result in a maximum pulse time limit of (0.625 ms * 255)

≥ 159 ms.

0x31 PULSE_THSX Register (Read/Write)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

THSX4

THSX3

THSX2

THSX1

THSX0

Table 45. PULSE_THSX Description

THSX4, THSX0

Pulse Threshold on X-axis. Default value: 0_0000

0x32 PULSE_THSY Register (Read/Write)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

THSY4

THSY3

THSY2

THSY1

THSY0

Table 46. PULSE_THSY Description

THSY4, THSY0

Pulse Threshold on Y-axis. Default value: 0_0000

0x33 PULSE_THSZ Register (Read/Write)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

THSZ4

THSZ3

THSZ2

THSZ1

THSZ0

Table 47. PULSE_THSZ Description

THSZ4, THSZ0

Pulse Threshold on Z-axis. Default value: 0_0000

0x34 PULSE_TMLT Register (Read/Write)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Tmlt7

Tmlt6

Tmlt5

Tmlt4

Tmlt3

Tmlt2

Tmlt1

Tmlt0

Table 48. Time Step for PULSE Time Limit at ODR and Power Mode

Output Data Rate (Hz)

Step at Normal Mode

Step at Low Power Mode

400

0.625 ms

1.25 ms

200

1.25 ms

2.5 ms

100

2.5 ms

5.0 ms

5 ms

10 ms

12.5

5 ms

10 ms

1.56

5 ms

10 ms

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