AN4662 datasheet(13/43 Pages) STMICROELECTRONICS

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AN4662

Startup 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.

after approximately 20 milliseconds, the device automatically enters power-down mode. To

turn on the device and gather acceleration data, it is necessary to select one of the Active

modes (Table 2: "Data rate configuration") and to enable at least one of the axes through

the CTRL1 register.

The following general-purpose sequence can be used to configure the device:

Write CTRL1 = 3Fh

// X, Y, Z, enabled, ODR = 100 Hz, BDU enabled

Write CTRL3 = 01h

// Data Ready Interrupt on INT1

3.1

Reading acceleration data

3.1.1

Using the status register

The device is provided with a STATUS register which should be polled to check when a

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

Read STATUS

If STATUS(ZYXDA) == 0 then go to 1

If STATUS(ZYXOR) == 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

10.

Data processing

11.

Go to 1

The check performed at step #3 allows understanding whether the read rate is adequate

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

overwritten by new data, due to a slow read rate, the ZYXOR bit of STATUS register is set

to 1.

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

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

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