LPS331AP Datasheet, PDF (11/36 Pages) STMicroelectronics – MEMS pressure sensor: 260-1260 mbar absolute digital output barometer

LPS331AP
Digital interfaces
5.2.1
I²C operation
The transaction on the bus is started through a START (ST) signal. A start condition is
defined as a HIGH to LOW transition on the data line while the SCL line is held HIGH. After
this has been transmitted by the master, the bus is considered busy. The next byte of data
transmitted after the start condition contains the address of the slave in the first 7 bits and
the eighth bit tells whether the master is receiving data from the slave or transmitting data to
the slave. When an address is sent, each device in the system compares the first seven bits
after a start condition with its address. If they match, the device considers itself addressed
by the master.
The slave address (SAD) associated to the LPS331AP is 101110xb. The SDO/SA0 pad can
be used to modify the less significant bit of the device address. If the SA0 pad is connected
to voltage supply, LSb is ‘1’ (address 1011101b), otherwise if the SA0 pad is connected to
ground, the LSb value is ‘0’ (address 1011100b). This solution permits to connect and
address two different LPS331APs to the same I²C lines.
Data transfer with acknowledge is mandatory. The transmitter must release the SDA line
during the acknowledge pulse. The receiver must then pull the data line LOW so that it
remains stable low during the HIGH period of the acknowledge clock pulse. A receiver which
has been addressed is obliged to generate an acknowledge after each byte of data
received.
The I²C embedded in the LPS331AP behaves like a slave device and the following protocol
must be adhered to. After the start condition (ST) a slave address is sent, once a slave
acknowledge (SAK) has been returned, a 8-bit sub-address (SUB) will be transmitted: the 7
LSB represents the actual register address while the MSB enables address auto increment.
If the MSb of the SUB field is ‘1’, the SUB (register address) will be automatically increased
to allow multiple data read/write.
The slave address is completed with a Read/Write bit. If the bit was ‘1’ (Read), a repeated
START (SR) condition must be issued after the two sub-address bytes; if the bit is ‘0’ (Write)
the master will transmit to the slave with direction unchanged. Table 9 explains how the
SAD+read/write bit pattern is composed, listing all the possible configurations.
Table 9. SAD+Read/Write patterns
Command
SAD[6:1]
SAD[0] = SA0
Read
101110
0
Write
101110
0
Read
101110
1
Write
101110
1
R/W
SAD+R/W
1
10111001 (B9h)
0
10111000 (B8h)
1
10111011 (BBh)
0
10111010 (BAh)
Table 10.
Master
Slave
Transfer when master is writing one byte to slave
ST
SAD + W
SUB
DATA
SAK
SAK
SP
SAK
Table 11. Transfer when master is writing multiple bytes to slave
Master
ST
SAD + W
SUB
DATA
DATA
Slave
SAK
SAK
SAK
SP
SAK
Doc ID 022112 Rev 7
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