CONFIGURABLE SAMPLES PER SECONDS AND INTERRUPT SETTINGS
The device can be configured into 8 different samples per seconds including: 1 sample/second, 2 samples/second,
4 samples/second, 8 samples/second, 16 samples/second, 32 samples/second, 64 samples/second, and 120 samples/second,
The user can specify the samples per second for their particular application, deciding on the trade off between power
consumption and number of samples, this can be configured in the SR (0x08) register. Once the user configurable samples per
second is chosen, the device will update the data for all 3 axes in the register at a resolution of 6-bits/axis.
The user can choose to enable/disable any of the following interrupts in the INTSU (0x06) register: Front/Back Interrupt,
Up/Down/Left/Right Interrupt, Tap Detection Interrupt, GINT (real-time motion tracking), Shake on X-axis, Shake on Y-axis, and
Shake on Z-axis. If the GINT is enabled, real-time motion tracking can be configured to trigger an interrupt after every sensor
data update: 1s (1 sample/second), 500 ms (2 samples/second), 250 ms (4 samples/second), 125 ms (8 samples/second),
62.5 ms (16 samples/second), 31.25 ms (32 samples/second), 15.625 ms (64 samples/second), or 8.36 ms (120 samples/
second). If any of the shake axis interrupts are enabled; excessive agitation, greater than 1.3 g, will trigger an interrupt. If either
the Up/Down/Left/Right Interrupt or the Front/Back Interrupt is enabled, any change in orientation will generate an interrupt. When
the Auto-Wake feature is enabled, and the Auto-Sleep counter elapses an interrupt will occur. When the device is in Auto-Sleep
state, if a shake interrupt, tap interrupt, Delta G, or orientation detection interrupt occur, the device will go out of sleep state and
into wake state.
POWER SAVING FEATURES
The MMA7660FC includes a range of user configurable power saving features. The device’s samples per second can be set
over a wide range from 1 to 120 samples a second; the operating current is directly proportional to samples per second. The
analog supply AVDD can be powered down to put the MMA7660FC into Off Mode, which typically draws 0.4 µA. The Auto-Wake/
Sleep feature can toggle the sampling rate from a higher user selected samples per second to a lower user selected samples
per second, changing based on if motion is detected or not. The user can choose to use any of the above options to configure
the part and make it have the optimal power consumption level for the desired application.
TESTING THE LOGIC CHAIN
MMA7660FC can be put into Test Mode, which disables accelerometer measurements and instead allows the user to write
6-bit values directly to the three axis data registers, thus simulating real time accelerometer measurements. The state machine
will respond to these values according to the enabled features and functions, allowing them to be validated.
NOTE: MMA7660FC does not include an accelerometer self test function, which is typically an electrostatic force applied
to each axis to cause it to deflect.
FEATURES
The Sensor employs both analog and digital filtering to ensure low noise and accurate output when using the part for Shake,
Tap, or Orientation Detection. During Active Mode, the data is filtered and stored for each of the 3 axes at the specified following
measurement intervals: 1s (1 sample/second), 500 ms (2 samples/second), 250 ms (4 samples/second),
125 ms (8 samples/second), 62.5 ms (16 samples/second), 31.25 ms (32 samples/second), 15.625 ms (64 samples/second), or
8.36 ms (120 samples/second) or indicated in AMSR [2:0].
The 6-bit measurement data is stored in the XOUT (0x00), YOUT (0x01), and ZOUT (0x02) registers and is used to update
the Shake, Alert, Tap, PoLa[2:0] (updates Up, Down, Left, and Right position), and BaFro[1:0] (updates Back and Front position)
in the TILT (0x03) register used for orientation detection. The customer can configure the part by enabling a number of user-
desired interrupts in the INTSU (0x06) register. Once the interrupts are enabled a change in filtered readings will cause an
interrupt to occur depending on the output.
The filters that are being used by this sensor is the analog filtering, digital noise filtering of measurements used for orientation
detection and updated in the XOUT (0x00), YOUT (0x01), and ZOUT (0x02) registers. The filtering method used is to oversample
each axis by taking 32 readings, and then calculate the average for the output measurement data as a finite impulse response
filter.
Table 6. Feature Summary Table
Feature
Orientation Change
Shake
Will Generate Interrupt
When FBINT, PLINT = 1
When SHINTX, SHINTY, SHINTZ = 1
When PDINT = 1
Tap or Tilt
Auto-Wake/Sleep
X, Y, Z Data Update
When ASINT = 1
When GINT = 1
NOTE: Sensor Measurements are NOT taken in Standby Mode or in Test Mode.
MMA7660FC
Sensors
Freescale Semiconductor
11
FREESCALE [ Freescale ]
