AN2335 datasheet(19/40 Pages) STMICROELECTRONICS

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AN2335

About control registers

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6.2

CTRL_REG2 (21h)

Control register #2.

SIM bit selects the SPI Serial Interface Mode. When SIM is ‘0’ (default value) the 4-wire

interface mode is selected. The data coming from the device are sent to SDO pad. In 3-wire

interface mode output data are sent to SDA/SDI pad.

BOOT bit is used to refresh the content of internal registers stored in the flash memory

block. At the device power up the content of the flash memory block is transferred to the

internal registers related to trimming functions to permit a good behavior of the device itself.

If for any reason the content of trimming registers was changed it is sufficient to use this bit

to restore correct values. When BOOT bit is set to ‘1’ the content of internal flash is copied

inside corresponding internal registers and it is used to calibrate the device. These values

are factory trimmed, they are different for every accelerometer and normally they have not to

be changed. At the end of the boot process the BOOT bit is set again to ‘0’.

FDS bit enables (FDS=1) or bypass (FDS=0) the high pass filter in the signal chain of the

sensor.

HP FF_WU[2:1]. These bits enable (HP FF_WU=1) or bypass (HP FF_WU=0) the high pass

filter in interrupt generation blocks.

HP coeff[2:1]. These bits are used to configure high-pass filter cut-off frequency ft

accordingly to the table given below:

SIM

BOOT

FDS

FF_WU2

FF_WU1

HP coeff2

HP coeff1

SIM

SPI Serial Interface Mode selection. Default value: 0

(0: 4-wire interface; 1: 3-wire interface)

BOOT

Reboot memory content. Default value: 0

(0: normal mode; 1: reboot memory content)

FDS

Filtered Data Selection. Default value: 0

(0: internal filter bypassed; 1: data from internal filter sent to output register)

HP FF_WU2

High Pass filter enabled for FreeFall/WakeUp # 2. Default value: 0

(0: filter bypassed; 1: filter enabled)

HP FF_WU1

High Pass filter enabled for Free-Fall/Wake-Up #1. Default value: 0

(0: filter bypassed; 1: filter enabled)

HP coeff2

HP coeff1

High pass filter cut-off frequency configuration. Default value: 00

HPcoeff2,1

ft (Hz)

(DR=100 Hz)

ft (Hz)

(DR=400 Hz)

0.5

0.25

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