AN2381 datasheet(37/47 Pages) STMICROELECTRONICS

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AN2381

Application information

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Application information

6.1

Start-up sequence

Once the device is powered-up it automatically downloads the calibration coefficients from

the embedded flash to the internal registers. When the boot procedure is completed, i.e.

approximately after 5 milli-seconds, the device automatically enters power-down mode.

To turn-on the device and gather acceleration data it is necessary to write C7h inside

CTRL_REG1. With this command the three acceleration channels (i.e. X, Y and Z axis) are

enabled.

6.2

Reading acceleration data

6.2.1

Using the Status Register

The device is provided with a STATUS_REG which should be polled to check when a new

set of data is available. The reading procedure should be the following:

The check performed at step 3 allows to understand whether the reading rate is adequate

compared to the data production rate. In case one or more acceleration samples have been

overwritten by new data because of a reading rate too slow, the bit STATUS_REG(7) will be

set to 1.

The overrun bit are automatically cleared when all the data present inside the device have

been read and new data have not been produced in the meanwhile.

6.2.2

Using the Data-Ready Signal

The device may be configured to have one HW signal (RDY, pin #6) to determinate when a

new set of measurement data is available for reading. This signal is represented by

STATUS_REG(3) content. The signal is active high (data available) and it returns to logic

zero when the higher part of the data of all the enabled channels have been read. To use the

RDY signal, it is necessary to set the CTRL_REG2 to xxxx 01xx.

read STATUS_REG

if STATUS_REG(3)=0 then goto 1

if STATUS_REG(7)=1 then some data have been overwritten

read OUTX_L

read OUTX_H

read OUTY_L

read OUTY_H

read OUTZ_L

read OUTZ_H

data processing

goto 1

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