LSM6DSL datasheet(37/113 Pages) STMICROELECTRONICS

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LSM6DSL

Digital interfaces

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6.3

I2C serial interface

The LSM6DSL I2C is a bus slave. The I2C is employed to write the data to the registers,

whose content can also be read back.

The relevant I2C terminology is provided in the table below.

There are two signals associated with the I2C bus: the serial clock line (SCL) and the Serial

DAta line (SDA). The latter is a bidirectional line used for sending and receiving the data

to/from the interface. Both the lines must be connected to Vdd_IO through external pull-up

resistors. When the bus is free, both the lines are high.

The I2C interface is implemeted with fast mode (400 kHz) I2C standards as well as with the

standard mode.

In order to disable the I2C block, (I2C_disable) = 1 must be written in CTRL4_C (13h).

6.3.1

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 LSM6DSL is 110101xb. The SDO/SA0 pin can

be used to modify the less significant bit of the device address. If the SDO/SA0 pin is

connected to the supply voltage, LSb is ‘1’ (address 1101011b); else if the SDO/SA0 pin is

connected to ground, the LSb value is ‘0’ (address 1101010b). This solution permits to

connect and address two different inertial modules to the same I2C bus.

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 LSM6DSL 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, an 8-bit sub-address (SUB) is transmitted.

The increment of the address is configured by the CTRL3_C (12h) (IF_INC).

Table 11. I2C terminology

Term

Description

Transmitter

The device which sends data to the bus

Receiver

The device which receives data from the bus

Master

The device which initiates a transfer, generates clock signals and terminates a

transfer

Slave

The device addressed by the master

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