MMA8450QT datasheet(33/57 Pages) FREESCALE

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Sensors

Freescale Semiconductor

MMA8450Q

Figure 12. DBCNTM Bit Function

0x26: FF_MT_COUNT_1 Freefall Motion Count 1 Register

This register sets the number of debounce sample counts for the event trigger.

D7 - D0 define the number of debounce sample counts for the event trigger. When the debounce counter exceeds the

FF_MT_COUNT_1 value, a Freefall/Motion event flag is set. The time step used for the debounce sample count depends on the

ODR chosen (Table 37).

An ODR of 100 Hz and a FF_MT_COUNT_1 value of 15 would result in a debounce response time of 150 ms.

0x26 FF_MT_COUNT_1 Register (Read/Write)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Table 36. FF_MT_COUNT_1 Description

D[7-0]

Count value. Default value: 0000_0000

Table 37. FF_MT_COUNT_1 and FF_MT_COUNT_2 Relationship with the ODR

Output Data Rate (Hz)

Step

Duration Range

400

2.5 ms

2.5 ms – 0.63s

200

5 ms

5 ms – 1.275s

100

10 ms

10 ms – 2.55s

20 ms

20 ms – 5.1s

12.5

80 ms

80 ms – 20.4s

1.56

640 ms

640 ms – 163s

Low g Event on

Count Threshold

FF_MT

EA FF

all 3-axis

(Freefall)

Counter

Value

Low g Event on

Count Threshold

FF_MT

(a)

all 3-axis

(Freefall)

Counter

Value

Low g Event on

Count Threshold

FF_MT

EA FF

all 3-axis

(Freefall)

Counter

Value

DBCNTM = 1

(b)

EA FF

DBCNTM = 0

(c)

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