User Manual

Data sheet
BMP085
Page 12
BST-BMP085-DS000-06 | Revision 1.3 | August 2011 Bosch Sensortec
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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.
Table 3: Overview of BMP085 modes, selected by driver software via the variable
oversampling_setting
Mode
Parameter
oversampling_
setting
Internal
number
of
samples
Conversion
time
pressure
max. [ms]
Avg.
current @
1 sample/s
typ. [μA]
RMS
noise
typ. [hPa]
RMS
noise
typ. [m]
ultra low power 0 1 4.5 3 0.06 0.5
standard 1 2 7.5 5 0.05 0.4
high resolution 2 4 13.5 7 0.04 0.3
ultra high
resolution
3 8 25.5 12 0.03 0.25
The noise data is calculated as standard deviation of 10 data points. For further information on
noise characteristics see the relevant application note “Noise in pressure sensor applications”.
All modes can be performed at higher speeds, e.g. up to 128 times per second for standard
mode, with the current consumption increasing proportionally to the sample rate. This way the
noise can be decreased further by software averaging.
3.4 Calibration coefficients
The 176 bit E
2
PROM is partitioned in 11 words of 16 bit each. These contain 11 calibration
coefficients. Every sensor module has individual coefficients. Before the first calculation of
temperature and pressure, the master reads out the E
2
PROM data.
The data communication can be checked by checking that none of the words has the value 0 or
0xFFFF.
Table 4: Calibration coefficients
BMP085 reg adr
Parameter MSB LSB
AC1 0xAA 0xAB
AC2 0xAC 0xAD
AC3 0xAE 0xAF
AC4 0xB0 0xB1
AC5 0xB2 0xB3
AC6 0xB4 0xB5
B1 0xB6 0xB7
B2 0xB8 0xB9
MB 0xBA 0xBB
MC 0xBC 0xBD
MD 0xBE 0xBF