AN2847

Start-up sequence

Doc ID 15136 Rev 2

11/31

Figure 3.

Data-ready signal

2.4

Understanding acceleration data

The measured acceleration data are sent to the OUTX_H, OUTX_L, OUTY_H, OUTY_L,

OUTZ_H and OUTZ_L registers. These registers contain, respectively, the most significant

part and the least significant part of the acceleration signals acting on the X, Y and Z axes.

The complete acceleration data for the X (Y, Z) channel is given by the concatenation

OUTX_H & OUTX_L (OUTY_H & OUTY_L, OUTZ_H & OUTZ_L) and is expressed as a 2’s

complement number.

2.4.1

Data alignment

Acceleration data are represented as 16-bit numbers and are left justified.

2.4.2

Big-little endian selection

The LIS331DLH allows the swapping of the content of the lower and the upper part of the

acceleration registers (i.e. OUTX_H with OUTX_L), to be compliant with both little-endian

and big-endian data representations.

“Little endian” means that the low-order byte of the number is stored in memory at the

lowest address, and the high-order byte at the highest address (the little end comes first).

This mode corresponds to bit BLE in the CTRL_REG4 reset to 0 -default configuration-.

Conversely, “big endian” means that the high-order byte of the number is stored in memory

at the lowest address, and the low-order byte at the highest address.

2.4.3

Example of acceleration data

The following table provides a few basic examples of the data that will be read in the data

registers when the device is subject to a given acceleration. The values listed in the table

are based on the assumption that the device is perfectly calibrated (i.e., no offset, no gain

error, etc.) and show the effect of the BLE bit.