Sensors

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Freescale Semiconductor, Inc.

MMA7660FC

Tap Detection

The MMA7660FC also includes a Tap Detection feature that can be used for a number of different customer applications such

as button replacement. For example, a single tap can stop a song from playing and a double tap can play a song. This function

detects a fast transition that exceeds a user-defined threshold (PDET (0x09) register) for a set duration (PD (0x0A) register).

Tap Detection Setup

In order to enable Tap detection in the device the user must enable the Tap Interrupt in the INTSU (0x06) register and AMSR

[2:0] = 000 in the SR (0x08) register. In this mode, TILT (0x03) register, XOUT (0x00), YOUT (0x01), and ZOUT (0x02) registers

will update at the 120 samples/second.

The user can configure Tap Detection to be detected on X and/or Y and/or Z axes. The customer can configure this by

changing the XDA, YDA, and/or ZDA bit in the PDET (0x09) register. Detection for enabled axes is decided on an OR basis: If

the PDINT bit is set in the INTSU (0x06) register, the device reports the first axis for which it detects a tap by the Tap bit in the

TILT (0x03) register. When the Tap bit in the TILT (0x03) register is set, tap detection ceases, but the device will continue to

process orientation detection data. Tap detection will resume when the TILT (0x03) register is read.

NOTE: Delta G is available with any AMSR setting, when XDA = YDA = ZDA = 1 (PDET = 1). When the sampling rate

is less than 120 samples/second, the device can not detect tapping, but can detect small tilt angles (30 º angle

change) which can not be detected by orientation detection.

Shake Detection

The shake feature can be used as a button replacement to perform functions such as scrolling through images or web pages

on a Mobile Phone/PMP/PDA. The customer can enable the shake interrupt on any of the 3 axes, by enabling the SHINTX,

SHINTY, and/or SHINTZ in the INTSU (0x06) register.

MMA7660FC detects shake by examining the current 6-bit measurement for each axis in XOUT, YOUT, and ZOUT. The axes

that are tested for shake detection are the ones enabled by SHINTX, SHINTY, and/or SHINTZ. If a selected axis measures

greater that 1.3 or less than -1.3 g, then a shake is detected for that axis and an interrupt occurs. All three axes are checked

independently, but a common Shake bit in the TILT register is set when shake is detected in any one of the selected axes.

Therefore when all three (SHINTX, SHINTY, and/or SHINTZ) are selected the sensor will not know what axis the shake occurred.

When the TILT register is read the Shake bit is cleared during the acknowledge bit of the read access to that register and shake

detection monitoring starts again.

Auto-Wake/Sleep

The MMA7660FC has the Auto-Wake/Sleep feature that can be enabled for power saving. In the Auto-Wake function, the

device is put into a user specified low samples per second (1 sample/second, 8 samples/second, 16 samples/second, or

32 samples/second) in order to minimize power consumption. When the Auto-Wake is enabled and activity is detected such as

a change in orientation, pulse event, Delta G acceleration or a shake event, then the device wakes up. Auto-Wake will

automatically enable Auto-Sleep when the device is in wake mode and can therefore be configured to cause an interrupt on

wake-up, by configuring the part to either wake-up with a change in orientation, shake, or if using the part at 120 samples/second

tap detection. When the device is in Auto-Wake mode, the MODE (0x07) register, bit AWE is high. When the device has detected

a change in orientation, a tap shake, or Delta G (change in acceleration), the device will enter Auto-Sleep mode. In the Auto-

Sleep function, the device is put into any of the following user specified samples per seconds (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). In the Auto-Sleep mode, if no change in the orientation, shake or tap has occurred and the sleep counter has elapsed,

the device will go into the Auto-Wake mode. When the device is in the Auto-Sleep mode, the MODE (0x07) register, bit ASE is

high. The device can be programmed to continually cycle between Auto-Wake/Sleep.

NOTE: The device can either be powered on in Wake/Sleep state depending on ASE/AWE settings. If the AWE bit is

set, the device is powered on in, in sleep state. If the ASW bit is set, the device is powered on in, in wake state.

Table 8. Auto-Wake/Sleep Truth Table

Trigger Wake-up

Reset Sleep Counter

Trigger Sleep Mode

Orientation Detection Change

Yes

Yes

No

Shake

Yes

Yes

No

Delta G

(set with PD (0x0A) and PDET (0x09))

Yes

(XDA = YDA = ZDA = 0)

Yes

No

Pulse Detect (120 samples/second)

Yes

Yes

No

Sleep Counter Elapsed

No

No

Yes