Digital interfaces

LIS331DL

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5.1.1

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 LIS331DL is 001110xb. SDO pad can be used

to modify less significant bit of the device address. If SDO pad is connected to voltage

supply LSb is ‘1’ (address 0011101b) else if SDO pad is connected to ground LSb value is

‘0’ (address 0011100b). This solution permits to connect and address two different

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 has

been received.

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 will be transmitted: the 7

LSb represent 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 incremented

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 will have to be issued after the two sub-address bytes; if the bit is ‘0’

(Write) the Master will transmit to the slave with direction unchanged.

Transfer when master is writing one byte to slave

Transfer when master is writing multiple bytes to slave:

Transfer when master is receiving (reading) one byte of data from slave:

Master

ST

SAD + W

SUB

DATA

SP

Slave

SAK

SAK

SAK

Master

ST

SAD + W

SUB

DATA

DATA

SP

Slave

SAK

SAK

SAK

SAK

Master

ST

SAD + W

SUB

SR

SAD + R

NMAK

SP

Slave

SAK

SAK

SAK

DATA