ADXL346ACCZ-R2 datasheet(23/40 Pages) AD

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Data Sheet

ADXL346

The DEVID register holds a fixed device ID code of 0xE6

(346 octal).

The THRESH_TAP register is eight bits and holds the threshold

value for tap interrupts. The data format is unsigned, so the

magnitude of the tap event is compared with the value in

THRESH_TAP for normal tap detection. For information on

improved tap detection, refer to the Improved Tap Detection

section. The scale factor is 62.5 mg/LSB (that is, 0xFF = +16 g).

A value of 0 may result in undesirable behavior if single-tap/

double-tap interrupts are enabled.

OFSY, OFSZ (Read/Write)

The OFSX, OFSY, and OFSZ registers are each eight bits and

offer user-set offset adjustments in twos complement format

with a scale factor of 15.6 mg/LSB (that is, 0x7F = 2 g). The

values stored in the offset registers are automatically added to

the acceleration data, and the resulting value is stored in the

output data registers. For additional information regarding

offset calibration and the use of the offset registers, refer to the

Offset Calibration section.

The DUR register is eight bits and contains an unsigned time

value representing the maximum time that an event must be

above the THRESH_TAP threshold to qualify as a tap event. For

information on improved tap detection, refer to the Improved Tap

Detection section. The scale factor is 625 µs/LSB. A value of 0

disables the single-tap/double-tap functions.

The latent register is eight bits and contains an unsigned time

value representing the wait time from the detection of a tap

event to the start of the time window (defined by the window

For information on improved tap detection, refer to the Improved

Tap Detection section. The scale factor is 1.25 ms/LSB. A value of 0

disables the double-tap function.

The window register is eight bits and contains an unsigned time

value representing the amount of time after the expiration of the

latency time (determined by the latent register) during which a

second valid tap can begin. For information on improved tap

detection, refer to the Improved Tap Detection section. The scale

factor is 1.25 ms/LSB. A value of 0 disables the double-tap

function.

The THRESH_ACT register is eight bits and holds the threshold

value for detecting activity. The data format is unsigned, so the

magnitude of the activity event is compared with the value in the

THRESH_ACT register. The scale factor is 62.5 mg/LSB. A value

of 0 may result in undesirable behavior if the activity interrupt

is enabled.

The THRESH_INACT register is eight bits and holds the threshold

value for detecting inactivity. The data format is unsigned, so the

magnitude of the inactivity event is compared with the value in

the THRESH_INACT register. The scale factor is 62.5 mg/LSB. A

value of 0 may result in undesirable behavior if the inactivity

interrupt is enabled.

The TIME_INACT register is eight bits and contains an unsigned

time value representing the amount of time that acceleration

must be less than the value in the THRESH_INACT register for

inactivity to be declared. The scale factor is 1 sec/LSB. Unlike

the other interrupt functions, which use unfiltered data (see the

Threshold section), the inactivity function uses filtered output

data. At least one output sample must be generated for the

inactivity interrupt to be triggered. This results in the function

appearing unresponsive if the TIME_INACT register is set to a

value less than the time constant of the output data rate. A value

of 0 results in an interrupt when the output data is less than the

value in the THRESH_INACT register.

ACT ac/dc

ACT_X enable

ACT_Y enable

ACT_Z enable

INACT ac/dc

INACT_X enable

INACT_Y enable

INACT_Z enable

ACT AC/DC and INACT AC/DC Bits

A setting of 0 selects dc-coupled operation, and a setting of 1

enables ac-coupled operation. In dc-coupled operation, the

current acceleration magnitude is compared directly with

THRESH_ACT and THRESH_INACT to determine whether

activity or inactivity is detected.

In ac-coupled operation for activity detection, the acceleration

value at the start of activity detection is taken as a reference

value. New samples of acceleration are then compared to this

reference value, and if the magnitude of the difference exceeds

the THRESH_ACT value, the device triggers an activity interrupt.

Similarly, in ac-coupled operation for inactivity detection, a

reference value is used for comparison and is updated whenever

the device exceeds the inactivity threshold. After the reference

value is selected, the device compares the magnitude of the

difference between the reference value and the current acceleration

with THRESH_INACT. If the difference is less than the value in

THRESH_INACT for the time in TIME_INACT, the device is

considered inactive and the inactivity interrupt is triggered.

Rev. C | Page 23 of 40

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