ADXL362 Просмотр технического описания (PDF) - Analog Devices

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ADXL362

Micropower, 3-Axis, ±2 g/±4 g/±8 g Digital Output MEMS Accelerometer

Analog Devices 

ADXL362

Data Sheet

When using referenced inactivity detection, inactivity is detected

when acceleration samples are within a user specified amount

of an internally defined reference (as described by Equation 2)

for a user defined amount of time.

ABS(Acceleration − Reference) < Threshold

(2)

Referenced inactivity, like referenced activity, is particularly

useful for eliminating the effects of the static acceleration due to

gravity. With absolute inactivity, if the inactivity threshold is set

lower than 1 g, a device resting motionless may never detect

inactivity. With referenced inactivity, the same device under the

same configuration detects inactivity.

The inactivity timer can be set to anywhere from 2.5 ms (a single

sample at 400 Hz ODR) to almost 90 minutes (65,535 samples

at 12.5 Hz ODR) of inactivity. A requirement for inactivity detec-

tion is that for whatever period of time the inactivity timer has

been configured, the accelerometer detects inactivity only when

it has been stationary for that amount of time.

For example, if the accelerometer has been configured for

90 minutes, the accelerometer detects inactivity when it has

been stationary for 90 minutes. The wide range of timer settings

means that in applications where power conservation is critical,

the system can be put to sleep after very short periods of inactivity.

In applications where continuous operation is critical, the system

stays on for as long as any motion is present.

Linking Activity and Inactivity Detection

The activity and inactivity detection functions can be used

concurrently and processed manually by a host processor, or

they can be configured to interact in several other ways, as

follows.

Default Mode

The user must enable the activity and inactivity functions because

these functions are not automatically enabled by default. After

the user enables the activity and inactivity functions, the ADXL362

exhibits the following behavior when it enters default mode: Both

activity and inactivity detection remain enabled and all interrupts

must be serviced by a host processor; that is, a processor must

read each interrupt before it is cleared and can be used again.

Loop mode operation is illustrated in the flowchart in Figure 32.

Linked Mode

In linked mode, activity and inactivity detection are linked to

each other such that only one of the functions is enabled at any

given time. As soon as activity is detected, the device is assumed

to be moving (or awake) and stops looking for activity; rather,

inactivity is expected as the next event. Therefore, only inactivity

detection operates.

Similarly, when inactivity is detected, the device is assumed to

be stationary (or asleep). Thus, activity is expected as the next

event; therefore, only activity detection operates.

WAIT FOR

ACTIVITY

EVENT

WAIT FOR

PROCESSOR TO

CLEAR INTERRUPT

AWAKE = 1

ACTIVITY

INTERRUPT

TRIGGERS

WAIT FOR

PROCESSOR TO

CLEAR INTERRUPT

INACTIVITY

INTERRUPT

TRIGGERS

AWAKE = 1

WAIT FOR

INACTIVITY

EVENT

NOTES

1. THE AWAKE BIT DEFAULTS TO 1 WHEN ACTIVITY AND INACTIVITY

ARE NOT LINKED.

Figure 31. Flowchart Illustrating Activity and Inactivity Operation in Default Mode

In linked mode, each interrupt must be serviced by a host

processor before the next interrupt is enabled.

Linked mode operation is illustrated in the flowchart in Figure 32.

WAIT FOR

ACTIVITY

EVENT

WAIT FOR

PROCESSOR TO

CLEAR INTERRUP

AWAKE = 0 INACTIVITY

INTERRUPT

ACTIVITY

INTERRUPT

AWAKE = 1

WAIT FOR

PROCESSOR TO

CLEAR INTERRUPT

WAIT FOR

INACTIVITY

EVENT

Figure 32. Flowchart Illustrating Activity and Inactivity Operation in Linked Mode

Loop Mode

In loop mode, motion detection operates as described in the

Linked Mode section, but interrupts do not need to be serviced

by a host processor. This configuration simplifies the implemen-

tation of commonly used motion detection and enhances power

savings by reducing the amount of power used in bus communi-

cation.

Loop mode operation is illustrated in the flowchart in Figure 33.

AWAKE = 1

WAIT FOR

ACTIVITY

EVENT

WAIT FOR

INACTIVITY

EVENT

AWAKE = 0

Figure 33. Flowchart Illustrating Activity and Inactivity Operation in Loop Mode

Autosleep

When in linked or loop mode, enabling autosleep causes the

device to enter wake-up mode autonomously (see the Wake-Up

Mode section) when inactivity is detected, and to reenter

measurement mode when activity is detected.

The autosleep configuration is active only if linked or loop modes

are enabled. In the default mode, the autosleep setting is ignored.

Rev. E | Page 16 of 43

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