AN2381 datasheet(22/47 Pages) STMICROELECTRONICS

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Registers Description

AN2381

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5.2.2

CTRL_REG2 (21h)

Control register #2

FS bit is used to select Full Scale value. After the device power-up the default full scale

value is +/-2g. In order to obtain a +/-6g full scale it is necessary to set FS bit to ‘1’.

BDU bit is used to inhibit output registers update until both upper and lower register parts

are read. In default mode (BDU= ‘0’) the output register values are updated continuously. If

for any reason it is not sure to read faster than output data rate it is recommended to set

BDU bit to ‘1’. In this way the content of output registers is not updated until both MSB and

LSB are read avoiding to read values related to different sample time.

BLE bit is used to select Big Endian or Little Endian representation for output registers. In

Big Endian’s one, MSB acceleration value is located at addresses 28h (X-axis), 2Ah (Y-axis)

and 2Ch (Z-axis) while LSB acceleration value is located at addresses 29h (X-axis), 2Bh (Y-

axis) and 2Dh (Z-axis). In Little Endian representation (default choice) the order is inverted

(refer to data register description for more details).

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 and they are different for every accelerometer. They permit a good

behavior of the device and normally they have not to be changed. At the end of the boot

process the BOOT bit is set again to ‘0’.

BDU

BLE

BOOT

IEN

DRDY

SIM

DAS

Full Scale selection. Default value: 0

(0: +/- 2g; 1: +/- 6g)

BDU

Block Data Update. Default value: 0

(0: continuous update; 1: output registers not updated until MSB and LSB reading)

BLE

Big/Little Endian selection. Default value: 0

(0: little endian; 1: big endian)

BOOT

Reboot memory content. Default value: 0

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

IEN

Interrupt Enable. Default value: 0

(0: data-ready on RDY pad; 1: interrupt signal on RDY pad)

DRDY

Enable Data-Ready generation. Default value: 0

(0: data-ready gen. disabled; 1: enable data-ready generation)

SIM

SPI Serial Interface Mode selection. Default value: 0

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

DAS

Data Alignment Selection. Default value: 0

(0: 12 bit right justified; 1: 16 bit left justified)

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