AN2335 datasheet(31/40 Pages) STMICROELECTRONICS

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AN2335

Application Information

31/40

Application Information

9.1

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 3 milli-seconds, the device automatically enters power-down mode.

To turn-on the device and gather acceleration data it is necessary to write 47h inside the

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

enabled and the Output Data Rate is set to 100 Hz.

9.2

READING ACCELERATION DATA

9.2.1

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.

9.2.2

Using the Data-Ready Signal

The device may be configured to generate one HW signal (Data Ready) on either pin 8 or 9

to flag that a new set of measurement data is available for reading. This signal corresponds

to the ZYXDA bit present inside the STATUS_REG. The polarity of the signal is defined

through the IHL bit present inside the CTRL_REG3 and it is deasserted when the

acceleration data of all the enabled channels have been read. To enable Data Ready signal

on pin #8 (corresponding to INT1) it is necessary to set I1CFG[2:0] bit present inside the

CTRL_REG3 to 100. Conversely, to enable Data Ready signal on pin #9 (corresponding to

INT2) it is necessary to set I2CFG[2:0] bit present inside the CTRL_REG3 to 100.

read STATUS_REG

if STATUS_REG(3)=0 then goto 1

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

read OUTX

read OUTY

read OUTZ

data processing

goto 1

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