BMA020 datasheet(21/50 Pages) BOSCH

21 / 50 page

Data sheet

BMA020

Digital, triaxial acceleration sensor

Bosch Sensortec

Rev. 1.2

Page 21

30 May 2008

as copying and passing on to third parties. BOSCH and the symbol are registered trademarks of Robert Bosch GmbH, Germany.

Note: Specifications within this document are subject to change without notice.

3.5 Data registers

3.5.1 Acc_x, acc_y, acc_z

Acceleration values are stored in the following registers to be read out through serial interface.

acc_x (02h, 7-6; 03h, 7-0)

acc_y (04h, 7-6; 05h, 7-0)

acc_z (06h, 7-6; 07h, 7-0)

The description of the digital signals acc_x, acc_y and acc_z is “2’s complement”.

From negative to positive accelerations, the following sequence for the

±2g measurement range

can be observed (

±4g and ±8g correspondingly):

-2.000g

10 0000 0000

-1.996g

10 0000 0001

...

-0.004g

11 1111 1111

0.000g

:00 0000 0000

+0.004g

00 0000 0001

...

+1.992g

01 1111 1110

+1.996g

01 1111 1111

Data is periodically updated (rate 3kHz) with values from the digital filter output. LSB

acceleration bytes must be read first. After an acceleration LSB byte read access, the

corresponding MSB byte update can optionally be blocked until it is also accessed for read.

Thus, MSB / LSB mix from different samples can be avoided (section 3.1.6).

It is not possible to read-out only MSB bytes if shadow_dis=0, an LSB byte must first be read

out. To be able to read out only MSB byte, shadow_dis must be written to 1.

new_data_* flags on bits 0 of acc_x (LSB), acc_y (LSB) and acc_z (LSB) can be used to detect

if acceleration values have already been read out (section 3.5.3).

If systematic acceleration values read out is planned (for signal processing by the

microcontroller), the interrupt pad can be programmed to flag the new data (section 3.2.10).

Every time all three axes values have been updated, the interrupt goes high and microcontroller

can read out data. With this method, microcontroller accesses are synchronized with internal

sensor IC updates.

Synchronization of read-out sequence has several advantages:

− it enables a constant phase shift between acceleration conversion and its corresponding

digital value read by microprocessor

− it reduces interface communication by avoiding over-sampling.

− potential noise due to serial interface activity perturbation would always be generated

during a less critical phase of the conversion cycle. The maximum delay advised to start

read out acceleration data is 20µs after INT high (window 0-80µs).

BMA020 Datasheet(PDF) 21 Page - Bosch Sensortec GmbH

BMA020 Datasheet(HTML) 21 Page - Bosch Sensortec GmbH

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

Datasheet Download

Link URL