AN2960 datasheet(32/41 Pages) STMICROELECTRONICS

32 / 41 page

Application information

AN2960

32/41

Doc ID 15557 Rev 1

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 complete (after

approximately 3 ms) the device automatically enters power-down mode.

To turn-on the device and gather acceleration data, it is necessary to write 47h in 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 permits understanding of 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 too slow reading rate, the bit

STATUS_REG(7) is set to 1.

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

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

9.2.2

Using the DataReady signal

The device may be configured to generate one HW signal (DataReady) on either pin 9 or 11,

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

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

the IHL bit present in CTRL_REG3 and is deasserted when the acceleration data of all the

enabled channels have been read. To enable the DataReady signal on pin 11

(corresponding to INT1), it is necessary to set the I1CFG[2:0] bit present in CTRL_REG3 to

100. Conversely, to enable the DataReady signal on pin 9 (corresponding to INT2) it is

necessary to set the I2CFG[2:0] bit present in 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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