Start-up sequence

AN2847

8/31

Doc ID 15136 Rev 2

2.1

Reading acceleration data

2.1.1

Using the status register

The device features a STATUS_REG register which should be polled to check when a new

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

The check performed at step 3 determines whether the reading rate is adequate compared

to the data production rate. In cases where one or more acceleration samples have been

overwritten by new data due to an excessively slow reading rate, the ZYXOR bit of the

STATUS_REG register 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.

2.1.2

Using the data-ready signal

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

measurement data is available for reading. This signal is represented by the XYZDA bit of

the STATUS_REG register. The signal can be driven to the INT1 or INT2 pins and its polarity

set to active-low or active-high through the CTRL_REG3 register. The interrupt is reset

when the higher part of the data of all the enabled channels has been read.

2.1.3

Using the block data update feature

If the reading of the acceleration data is particularly slow and cannot be (or does not need to

be) synchronized with either the XYZDA bit within the STATUS_REG or with the RDY signal,

it is strongly recommended to set the BDU (block data update) bit in CTRL_REG4 to 1.

This feature prevents the need to read the values (most significant and least significant parts

of the acceleration data) related to different samples. In particular, when the BDU is

activated, the data registers related to each channel always contain the most recent

acceleration data produced by the device. But if the reading of a given pair (i.e. OUTX_H

and OUTX_L, OUTY_H and OUTY_L, OUTZ_H and OUTZ_L) is initiated, the refresh for

that pair is blocked until both the MSB and LSB parts of the data are read.

1

read STATUS_REG

2

if STATUS_REG(3) = 0 then goto 1

3

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

4

read OUTX_L

5

read OUTX_H

6

read OUTY_L

7

read OUTY_H

8

read OUTZ_L

9

read OUTZ_H

10

data processing

11

goto 1