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MMA8450Q

0x2D: TRANSIENT_THS Transient Threshold Register

The TRANSIENT_THS register sets the threshold limit for the high pass filtered acceleration. The value in the

TRANSIENT_THS register corresponds to a g value which is compared against the values of OUT_X_DELTA, OUT_Y_DELTA,

and OUT_Z_DELTA. If the acceleration exceeds the threshold limit an event flag is raised and an interrupt is generated if

interrupts are enabled.

The minimum threshold resolution is dependent on the selected acceleration g range and the threshold register has a range

of 0 to 127.

Therefore:

•

If the selected acceleration g range is 8g mode (FS = 11), the minimum threshold resolution is 0.063g/LSB. The maximum

is 8g.

•

If the selected acceleration g range is 4g mode (FS = 10), the minimum threshold resolution is 0.0315g/LSB. The

maximum is 4g.

•

If the selected acceleration g range is 2g mode (FS = 01), the minimum threshold resolution is 0.01575g/LSB. The

maximum is 2g.

•

The DBCNTM bit behaves in the same manner described previously for the Motion/Freefall 1.

0x2E: TRANSIENT_COUNT Transient Debounce Register

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

unsigned value of OUT_X_DELTA or OUT_Y_DELTA or OUT_Z_DELTA register 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.

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

Table 39. TRANSIENT_SRC Description

Event Active Flag. Default value: 0

0: No event flag asserted; 1: one or more event flag has been asserted.

ZTRANSE

Z transient event. Default value: 0

0: No Z event detected, 1: Z event detected

YTRANSE

Y transient event. Default value: 0

0: No Y event detected, 1: Y event detected

XTRANSE

X transient event. Default value: 0

0: No X event detected, 1: X event detected

0x2D 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 40. 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

0x2E TRANSIENT_COUNT Register (Read/Write)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Table 41. TRANSIENT_COUNT Description

D[7-0]

Count value. Default value: 0000_0000

Table 42. TRANSIENT_COUNT relationship with the ODR

Output Data Rate (Hz)

Step

Duration Range

400

2.5 ms

2.5 ms – 0.637s

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

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