SMD500 Datasheet, PDF (5/10 Pages) List of Unclassifed Manufacturers – Altimeter / Barometer Module ultra low power, low voltage

3.1. Calibration coefficients
The 64 bit PROM is partitioned in four words F1 to F4 of 16 bit each. These 64 bits contain six calibration coefficients AC1 to AC6
as shown in table 2. Each sensor module has individual coefficients. Before the first calculation of temperature and pressure, the
master reads out the PROM data words F1 to F4 and converts them into the six calibration coefficients AC1 to AC6 using the C
code function SMD500_convertPROMdata.
Then the function SMD500_init_calB1B2 calculates the two derived coefficients B1 and B2 as shown in figure 3.
Table 2: PROM mapping of the six coefficients AC1 to AC6
bit 15 bit 14 bit 13 bit 12 bit 11 bit 10 bit 9 bit 8 bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
F1 AC2_1 AC2_0 AC1_13 AC1_12 AC1_11 AC1_10 AC1_9 AC1_8 AC1_7 AC1_6 AC1_5 AC1_4 AC1_3 AC1_2 AC1_1 AC1_0
F2 AC2_8 AC2_7 AC2_6 AC2_5 AC2_4 AC2_3 AC2_2 AC3_8 AC3_7 AC3_6 AC3_5 AC3_4 AC3_3 AC3_2 AC3_1 AC3_0
F3 AC5_2 AC5_1 AC5_0 AC4_12 AC4_11 AC4_10 AC4_9 AC4_8 AC4_7 AC4_6 AC4_5 AC4_4 AC4_3 AC4_2 AC4_1 AC4_0
F4 AC5_6 AC5_5 AC5_4 AC5_3 AC6_11 AC6_10 AC6_9 AC6_8 AC6_7 AC6_6 AC6_5 AC6_4 AC6_3 AC6_2 AC6_1 AC6_0
St art
Read calibrat ion dat a
from t he PROM of t he SMD500
F1, F2, F3, F4
(4 x 16 bit)
Convert calibrat ion dat a int o calibrat ion
coefficient s (see t able 2)
AC1
(14 bit)
AC2
(9 bit)
AC3
(9 bit)
AC4
(13 bit)
AC5
(7 bit)
AC6
(12 bit)
exam p l e:
F1 =
F2 =
F3 =
F4 =
40851
29891
21009
38946
AC1 =
AC2 =
AC3 =
AC4 =
AC5 =
AC6 =
8083
234
195
4625
74
2082
C code function:
SMD500_convert PROMdat a
calculat e coefficient B1 and B2
B1 = ((AC3 - 1984) * (-17268)) / 2¹¹ - 8970
B2 = ((AC2 - 457) * B1 / 2⁴) / (AC3 - 1984)
Figure 3: Initial calculations for the SMD500
B1 =
B2 =
6114
47
SMD500_init _calB1B2
3.2. Calculating pressure and temperature
The calculation of temperature in °C and pressure in Pa is shown in figure 4. This corresponds to the C code functions
SMD500_caltemperature, SMD500_calB3, SMD500_calB4 and SMD500_calpressure.
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