DA5534_022.doc
July 17th, 2002
12
ECN493
Serial interface
The MS5534 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 MS5534 on the rising edge of SCLK and each Bit being sent by
the MS5534 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 MS5534 with the falling edge of SCLK. The SCLK-signal is generated by the
microprocessor’s system. The digital data provided by the MS5534 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
“D1”
(Figure 6a)
• Conversion start for temperature measurement and ADC-data-out
“D2”
(Figure 6b)
• Calibration data read-out sequence for word 1
(Figure 6c)
• Calibration data read-out sequence for word 2
(Figure 6d)
• Calibration data read-out sequence for word 3
(Figure 6c)
• Calibration data read-out sequence for word 4
(Figure 6d)
• RESET sequence
(Figure 6e)
Every communication starts with an instruction sequence at pin DIN. Fig. 6 shows the timing diagrams for the
MS5534. 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 during the last bit of the Stop Sequence.
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 read-out 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 its unique pattern is recognized by the module in any state. By consequence
it can be used to restart if synchronization between the microcontroller and the MS5534 has been lost. This
sequence is 21-Bit long. The DOUT signal might change during that sequence (see Fig. 6e).
It is thus recommended to send the RESET-Sequence before each Conversion Sequence to avoid
hanging up the protocol permanently in case of electrical interference.
sequence: START+P-measurement
Bit7
Conversion start for pressure measurement and ADC-data-out "D1":
end of conversion
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0
conversion
(33ms)
DB7
ADC-data out MSB
ADC-data out LSB
Bit8 Bit9
Start-bit
Stop-bit
DB6 DB5 DB4 DB3 DB2 DB1
DB0
DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
start of conversion
Setup-bits
Fig. 6a: D1 acquisition sequence
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