AN3393 datasheet(13/103 Pages) STMICROELECTRONICS

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AN3393

Startup sequence

103

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 5 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

operating modes and enable at least one of the axes through the CTRL_REG4 register.

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

2.1

Reading acceleration data

2.1.1

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 reads should be performed as follows:

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

adequate compared to the data generation rate. In the case one or more acceleration

samples have been overwritten by new data, because of an insufficient reading rate, the

ZYXOR bit of STATUS is set to 1.

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

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

2.1.2

Using the data-ready (DRY) signal

The device may be configured to have one HW signal to determine when a new set of

measurement data is available for reading. The signal can be driven to the INT1 pin by

1. Write CTRL_REG4 = 67h

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

2. Write CTRL_REG3 = C8h

// DRY active high on INT1 pin

Read STATUS

If STATUS(3) = 0, then go to 1

If STATUS(7) = 1, then some data have been overwritten

Read OUT_X_L

Read OUT_X_H

Read OUT_Y_L

Read OUT_Y_H

Read OUT_Z_L

Read OUT_Z_H

10.

Data processing

11.

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