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MMA7450L

±2g/±4g/±8g Three Axis Low-g Digital Output Accelerometer

Freescale Semiconductor 

When measurements on all three axes are complete, a

logic high level is output to the DRDY pin, indicating

“Measurement data is ready.” The DRDY status can be

monitored by the DRDY bit in Status Register (Address: $09).

The DRDY pin is kept high until one of the three Output Value

Registers are read. If the next measurement data is written

before the previous data is read, the DOVR bit in the Status

Register will be set. Also note that In measurement mode,

level detection mode and pulse detection mode are not

available.

LEVEL DETECTION MODE

Level Detection Mode

In level detection mode, the measurements for x, y and z

are all enabled with 2g/4g and 8g range available.The

detection of thresholds for an acceleration signal level for the

combinations of x and y or x, y, and z is enabled. This is used

for motion detection where the threshold can be user set

depending on the application or user specific requirements.

When a motion event is detected, one of the interrupt pins

(INT1 or INT2) will output a logic high output signaling the

event is detected.

Setting for Motion Detection

To configure the MMA7450L for motion detection, after all

three axes are enabled for detection, set the LDPOL bit in

Control Register 2 (Address: $19) to 0. When the output

value of one of the enabled axes exceeds the threshold limit

value, either INT1 or INT2 pin will output a logic High

indicating the event was detected.

– If LDPOL = 0 and all three axes are enabled for

detection

– When the specified motion condition is detected, INT1

or INT2 will output a Logic high

– “XOUT ≥Threshold” or “YOUT ≥Threshold” or

“ZOUT ≥Threshold”

NOTE:

Measurement period and bandwidth for level

detection is different from data output rate and the

bandwidth of “measurement.” Please refer to

Functional Parameter for Detection for more

information.

PULSE DETECTION MODE

Pulse Detection Mode

In pulse detection mode, both 2g/4g and 8g range are

available. Measurements for x, y and z in 2g/4g or 8g mode

are enabled. The level detection is also enabled in this mode.

The pulse detected by the acceleration signal is enabled with

single pulse and double pulse detection allowing the choice

of either positive, negative or absolute value pulse detection.

Setting for Motion Detection

For the PDPOL bit in Control Register 2 (Address: $19) the

register should be set to “0” for motion detection. When the

output value of one of the enabled axes exceeds the

threshold limit value, logic high level is output to INT1 or INT2

pin and indicates the event was detected.

– If PDPOL = 0 and all three axes are enabled for

detection

– When the condition below was detected, logic high

level outputs to INT1 or INT2

– “XOUT ≥Threshold” or “YOUT ≥Threshold” or

“ZOUT ≥Threshold”

Setting for Free Fall Detection

To configure the MMA7450L for freefall detection, set the

PDPOL bit in Control Register 2 (Address: $19) to 1.

Threshold limit value is common for all three axes.

Positive/negative and absolute value option is available.

Assigning and Clearing the Interrupt Pins

INT1/INT2 pin assignment for level detection is controlled

by Control Register 1 (Address:$18).

INTPIN:

0:INT1 will be used for event

1:INT2 will be used for event

Detection status is able to be monitored by Detection

Source Register (Address:$0A). Once the configured event is

detected, INT pin or register bit will not be cleared until the

respective clear bit (CLRINT1 or CLRINT2) in Interrupt Latch

Reset Register (Address: $17) is set. CLRINT1 and CLRINT2

should be cleared before starting next detection. Otherwise,

INT pin or register will not set.

Next, set the register for Time Window for 2nd pulse value

(Address $1E) to 0.

When the output values of all enabled axes are below the

threshold limit continuously during the period specified in

Latency Timer Value Register, logic high level is output to

INT1 or INT2 pin indicating freefall was detected.

Filtering

The 3 axis accelerometer contains digital filtering.

MMA7450L

6

Sensors

Freescale Semiconductor

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