ADXL375 datasheet(21/32 Pages) AD

21 / 32 page

Data Sheet

ADXL375

Rev. 0 | Page 21 of 32

All registers in the ADXL375 are eight bits in length.

The read-only DEVID register holds the fixed device ID code

of 0xE5 (345 octal).

The THRESH_SHOCK register contains the unsigned threshold

value for shock interrupts. The magnitude of the shock event is

compared with the value in the THRESH_SHOCK register for

shock detection. The scale factor is 780 mg/LSB. A value of 0 may

result in undesirable behavior if single shock/double shock inter-

rupts are enabled.

OFSY, OFSZ (Read/Write)

The OFSX, OFSY, and OFSZ registers contain user-configured

offset adjustments in twos complement format with a scale factor

of 1.56 g/LSB. The value stored in the offset registers is automat-

ically added to the acceleration data, and the resulting value is

stored in the output data registers (Address 0x32 to Address 0x37).

For more information about offset calibration and the use of the

offset registers, see the Offset Calibration section.

The DUR register contains an unsigned time value representing

the maximum time that an event must be above the THRESH_

SHOCK threshold to qualify as a shock event. The scale factor

is 625 μs/LSB. A value of 0 disables the single shock and double

shock functions.

The latent register contains an unsigned time value representing

the wait time from the detection of a shock event to the start of

the time window (specified by the window register) during which

a possible second shock event can be detected. The scale factor

is 1.25 ms/LSB. A value of 0 disables the double shock function.

The window register contains an unsigned time value repre-

senting the amount of time after the expiration of the latency

time (specified by the latent register) during which a second

valid shock can begin. The scale factor is 1.25 ms/LSB. A value

of 0 disables the double shock function.

The THRESH_ACT register contains the unsigned threshold

value for detecting activity. The magnitude of the activity event

is compared with the value in the THRESH_ACT register. The

scale factor is 780 mg/LSB. A value of 0 may result in undesirable

behavior if the activity interrupt is enabled.

The THRESH_INACT register contains the unsigned threshold

value for detecting inactivity. The magnitude of the inactivity

event is compared with the value in the THRESH_INACT

in undesirable behavior if the inactivity interrupt is enabled.

The TIME_INACT register 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 detected. The scale factor is 1 sec/LSB. Unlike the other

interrupt functions, which use unfiltered output data (see the

Threshold Detection and Bandwidth section), the inactivity

function uses filtered output data.

At least one output sample must be generated for the inactivity

interrupt to be triggered. For this reason, the inactivity function

may appear to be 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. The maximum

value for TIME_INACT is 255 sec.

ACT AC/DC

ACT_X enable

ACT_Y enable

ACT_Z enable

INACT AC/DC INACT_X enable INACT_Y enable INACT_Z enable

The ACT_INACT_CTL register selects dc-coupled or ac-coupled

operation and selects the axes that participate in activity and

inactivity detection.

ACT AC/DC and INACT AC/DC Bits

A setting of 0 for the ACT AC/DC and INACT AC/DC bits

selects dc-coupled operation; a setting of 1 selects ac-coupled

operation. In dc-coupled operation, the current acceleration

magnitude is compared directly with the values in the THRESH_

ACT and THRESH_INACT registers 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 data are then compared to this ref-

erence value and, if the magnitude of the difference exceeds the

THRESH_ACT value, an activity interrupt is triggered.

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

ence 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 the

THRESH_INACT value. If the difference is less than the value

in the THRESH_INACT register for the time specified in the

TIME_INACT register, the device is considered inactive, and

the inactivity interrupt is triggered.

ADXL375 数据表(PDF) 21 Page - Analog Devices

ADXL375 数据表(HTML) 21 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

数据表下载