LSM9DS1 Datasheet, PDF (29/72 Pages) –

LSM9DS1
Digital interfaces
5.1.1
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.
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 inside the LSM9DS1 behaves like a slave device and the following
protocol must be adhered to. In the I²C of the accelerometer and gyroscope sensor, after
the start condition (ST) a slave address is sent, once a slave acknowledge (SAK) has been
returned, an 8-bit sub-address (SUB) is transmitted. The 7 LSb represent the actual register
address while the CTRL_REG8 (22h) (IF_ADD_INC) bit defines the address increment. In
the I²C of the magnetometer sensor, after the START condition (ST) a slave address is sent,
once a slave acknowledge (SAK) has been returned, an 8-bit sub-address (SUB) is
transmitted. The 7 LSb represent the actual register address while the MSB enables the
address auto increment. The SUB (register address) is automatically increased to allow
multiple data read/write.
Master
Slave
Table 15. Transfer when master is writing one byte to slave
ST
SAD + W
SUB
DATA
SAK
SAK
SP
SAK
Table 16. Transfer when master is writing multiple bytes to slave
Master ST SAD + W
SUB
DATA
DATA
SP
Slave
SAK
SAK
SAK
SAK
Table 17. Transfer when master is receiving (reading) one byte of data from slave
Master ST SAD + W
SUB
SR SAD + R
NMAK SP
Slave
SAK
SAK
SAK DATA
Table 18. Transfer when master is receiving (reading) multiple bytes of data from slave
Master ST SAD+W
SUB
SR SAD+R
MAK
MAK
NMAK SP
Slave
SAK
SAK
SAK DATA
DATA
DATA
Data are transmitted in byte format (DATA). Each data transfer contains 8 bits. The number
of bytes transferred per transfer is unlimited. Data is transferred with the Most Significant bit
(MSb) first. If a receiver can’t receive another complete byte of data until it has performed
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