Sensors

Freescale Semiconductor

7

MMA7455L

Measurement Mode

During measurement mode, continuous measurements on

all three axes enabled. The g-range for 2g, 4g, or 8g are

selectable with 8-bit data and the g-range of 8g is selectable

with 10-bit data. The sample rate during measurement mode

is 125 Hz with 62.5 BW filter selected. The sample rate is

250 Hz with the 125 Hz filter selected. Therefore, when a

conversion is complete (signaled by the DRDY flag), the next

measurement will be ready.

When measurements on all three axes are completed, 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 one, two or all three axes can be enabled. This is typically 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 MMA7455L for motion detection, after all three axes are enabled for detection, set the LDPL 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 LDPL = 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”

Threshold limit value is common for all three axes. Positive/negative and absolute value option is available

Setting for Freefall Detection

LDPL bit in Control Register 2 (Address: $19) should be “1” for freefall detection. When the output values of all enabled axes

are below the threshold limit value, logic high level is output to INT1 or INT2 pin and indicates the event was detected.

–

If LDPL = 1 and all three axes are enabled for detection

–

When the condition below was detected, Logic high level output to INT1 or INT2

–“XOUT

≤Threshold" and “YOUT ≤Threshold" and ”ZOUT≤Threshold"

–

Threshold limit value is common for all three axes. Positive/negative and absolute value option is available.

–

INT1/INT2 pin assignment for level detection is controlled by Control Register 1 (Address: $18). Detection status is also

able to be monitored by Detection source Register (Address: $0A). Once the event was detected, INT pin or register bit

will not be cleared until clear bit in Interrupt Latch Reset Register (Address: $17) is set.

For a more detailed description of the Threshold Detect please refer to application note AN3571, “Threshold and Pulse Detect

Using the MMA745xL”.

$19

CTL2

—————

DRVO

PDPL

LDPL