ADXL366 datasheet(24/71 Pages) AD

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Data Sheet

ADXL366

POWER SAVINGS FEATURES

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Rev. 0 | 24 of 71

Linking Activity and Inactivity Detection

The activity and inactivity detection functions can be used concur-

rently and processed manually by a host processor, or they can

be configured to interact in several other ways, shown in the

Default Mode section, Linked Mode section, Loop Mode section,

and Autosleep section.

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, 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.

Default mode operation is shown in the flowchart in Figure 49.

Figure 49. Flowchart Illustrating Activity and Inactivity Operation in Default

Mode

Linked Mode

In linked mode, activity and inactivity detection are linked to each

other in a way so 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. 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). Therefore, activity is expected as the next

event and only activity detection operates.

In linked mode, activity interrupt is enabled first after power-up.

Each interrupt must be serviced by a host processor before the next

interrupt is enabled.

Note that the AWAKE bit is defined as follows:

►

On power-up, AWAKE = 1.

►

If inactivity is detected and inactivity interrupt is cleared, AWAKE

= 0.

►

If activity is detected and activity interrupt is cleared, AWAKE =

It is important to note that in linked mode, the host processor

must read the status register to update the activity and inactivity

thresholds in referenced mode. Otherwise, the thresholds do not

update as the acceleration changes.

Linked mode operation is shown in the flowchart in Figure 50.

Figure 50. 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 implementation of

commonly used motion detection and enhances power savings by

reducing the amount of power used in bus communication.

Similar to linked mode, activity interrupt is enabled first after power-

up in loop mode. Loop mode operation is shown in the flowchart in

Figure 51.

Figure 51. Flowchart Illustrating Activity and Inactivity Operation in Loop

Mode

Looped Mode Start-Up Routine

When using loop mode, it is important to note that the AWAKE bit is

always asserted when the device first enters measurement mode.

The device is currently waiting for an activity event. Therefore,

this AWAKE bit remains asserted until activity is detected and an

inactivity event is detected. To avoid this, the device must enter

measurement mode with an activity threshold less than the noise

level of the ADXL366 and an inactivity threshold greater than 1g,

which allows the device to de-assert the AWAKE bit immediately af-

ter entering measurement mode. The activity threshold can then be

raised to the desired level (while still in measurement mode). The

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