Bosch BMP581 - Page 22

Bosch Sensortec"| BST-BMP581-DS004-02 22 | 74
Modifications reserved | Data subject to change
without notice Document number: BST-BMP581-DS004-02
 shdw_sel_iir_t: select source for temperature data register
 fifo_sel_iir_t: select source for temperature FIFO
 shdw_sel_iir_p: select source for pressure data register
 fifo_sel_iir_p: select source for pressure FIFO
 oor_sel_iir_p: select source for pressure out-of-range interrupt
4.5 Data registers
Data from the most recent measurement is present in data registers. The DSP_CONFIG.swdw_sel_iir_t and
DSP_CONFIG.swdw_sel_iir_t select if IIR-filtered data or unfiltered data is presented in the data registers.
Temperature data is contained in the registers TEMP_DATA_MSB, TEMP_DATA_LSB, TEMP_DATA_XLSB. The
registers shall be interpreted in the following way:
T [°C] = (
__,__,__


)
Pressure data is contained in the registers PRESS_DATA_MSB, PRESS_DATA_LSB, PRESS_DATA_XLSB. The
registers shall be interpreted in the following way:
p
[Pa] = (
__,__,__


)
In both equations, the divisions can be implemented by a simple and efficient bit-wise right shift operation. To read out
data after a conversion, it is strongly recommended to use a burst read and not address every register individually.
4.5.1 Data Shadowing
In normal mode, measurement timing is not necessarily synchronized to readout. This means that new measurement
results may become available while the user is reading the results from the previous measurement. In this case,
shadowing is performed in order to guarantee data consistency. Shadowing will only work if all data registers are read
in a single burst read. Therefore, the user must use burst reads if he does not synchronize data readout with the
measurement cycle. Using several independent read commands may result in inconsistent data.
If a new measurement is finished and the data registers are still being read, the new measurement results are
transferred into shadow data registers. The content of shadow registers is transferred into data registers as soon as
the user ends the burst read, even if not all data registers were read. Reading across several data registers can
therefore only be guaranteed to be consistent within one measurement cycle if a single burst read command is used.
After the end of the burst read, all user data registers are updated at once with the shadowed data.
4.6 FIFO
The BMP581 contains a first-in first-out (FIFO) data buffer. Pressure and temperature data is stored in the FIFO in
frames. Each frame contains the data from one measurement. The maximum number of frames depends on which
data is stored in the FIFO:
 16 frames if both pressure and temperature are stored
 32 frames if only pressure or temperature is stored
4.6.1 FIFO Configuration
The FIFO frame type is selected by FIFO_SEL.fifo_frame_sel:
 0b00: FIFO not enabled