MS5541C Datasheet, PDF (14/21 Pages) Intersema Sensoric SA – MINIATURE 14 bar MODULE

MS5541-30C
Miniature 14 bar Module
SERIAL INTERFACE
The MS5541C communicates with microprocessors and other digital systems via a 3-wire synchronous serial
interface as shown in Fig. 1. The SCLK (Serial clock) signal initiates the communication and synchronizes the data
transfer with each bit being sampled by the MS5541C on the rising edge of SCLK and each bit being sent by the
MS5541C on the rising edge of SCLK. The data should thus be sampled by the microcontroller on the falling edge
of SCLK and sent to the MS5541C with the falling edge of SCLK. The SCLK-signal is generated by the
microprocessor’s system. The digital data provided by the MS5541C on the DOUT pin is either the conversion result
or the software calibration data. In addition, the signal DOUT (Data out) is also used to indicate the conversion
status (conversion-ready signal, see below). The selection of the output data is done by sending the corresponding
instruction on the pin DIN (Data input).
Following is a list of possible output data instructions:
 Conversion start for pressure measurement and ADC-data-out
 Conversion start for temperature measurement and ADC-data-out
 Calibration data read-out sequence for Word1
 Calibration data read-out sequence for Word2
 Calibration data read-out sequence for Word3
 Calibration data read-out sequence for Word4
 RESET sequence
“D1” (Figure 6a)
“D2” (Figure 6b)
(Figure 6c)
(Figure 6d)
(Figure 6c)
(Figure 6d)
(Figure 6e)
Every communication starts with an instruction sequence at pin DIN. Fig. 6 shows the timing diagrams for the
MS5541C. The device does not need a ‘Chip select’ signal. Instead there is a START sequence (3-Bit high) before
each SETUP sequence and STOP sequence (3-Bit low) after each SETUP sequence. The SETUP sequence
consists in 4-Bit that select a reading of pressure, temperature or calibration data. In case of pressure- (D1) or
temperature- (D2) reading the module acknowledges the start of a conversion by a low to high transition at pin
DOUT.
Two additional clocks at SCLK are required after the acknowledge signal. Then SCLK is to be held low by the
microcontroller until a high to low transition on DOUT indicates the end of the conversion.
This signal can be used to create an interrupt in the microcontroller. The microcontroller may now read out the 16
bit word by giving another 17 clocks on the SLCK pin. It is possible to interrupt the data READOUT sequence with
a hold of the SCLK signal. It is important to always read out the last conversion result before starting a new
conversion.
The RESET sequence is special as the module in any state recognizes its unique pattern. By consequence, it can
be used to restart if synchronization between the microcontroller and the MS5541C has been lost. This sequence
is 21-bit long. The DOUT signal might change during that sequence (see Fig. 6e). It is recommended to send the
RESET sequence before each CONVERSION sequence to avoid hanging up the protocol permanently in case of
electrical interference.
Conversion start for pressure measurement and ADC-data-out "D1":
end of conversion
start of conversion
sequence: START+P-measurement
Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7 Bit8 Bit9
S tart-b it
Setu p -b its
Sto p -b it
co n v ers io n
(3 3 ms )
ADC-data outMSB
DB7 DB6 DB5 DB4 DB3 DB2 DB1
ADC-data outLSB
DB0 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
Fig. 6a: D1 ACQUISITION sequence
SENSOR SOLUTIONS ///MS5541C
09/2015
Page 14