STA309B datasheet(15/66 Pages) STMICROELECTRONICS

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STA309B

I2C bus operation

Doc ID 022570 Rev 2

15/66

I2C bus operation

The STA309B supports the I2C protocol via the input ports SCL and SDA_IN (master to

slave) and the output port SDA_OUT (slave to master).

This protocol defines any device that sends data on to the bus as a transmitter and any

device that reads the data as a receiver.

The device that controls the data transfer is known as the master and the other as the slave.

The master always starts the transfer and provides the serial clock for synchronization. The

STA309B is always a slave device in all of its communications.

5.1

Communication protocol

5.1.1

Data transition or change

Data changes on the SDA line must only occur when the SCL clock is low. An SDA transition

while the clock is high is used to identify a START or STOP condition.

5.1.2

Start condition

START is identified by a high to low transition of the data bus SDA signal while the clock

signal SCL is stable in the high state. A START condition must precede any command for

data transfer.

5.1.3

Stop condition

STOP is identified by low to high transition of the data bus SDA signal while the clock signal

SCL is stable in the high state. A STOP condition terminates communication between the

STA309B and the bus master.

5.1.4

Data input

During the data input the STA309B samples the SDA signal on the rising edge of clock SCL.

For correct device operation the SDA signal must be stable during the rising edge of the

clock and the data can change only when the SCL line is low.

5.2

Device addressing

To start communication between the master and the Omega FFX core, the master must

initiate with a start condition. Following this, the master sends 8 bits to the SDA line (MSB

first) corresponding to the device select address and read or write mode.

The 7 most significant bits are the device address identifiers, corresponding to the I2C bus

definition. In the STA309B the I2C interface has two device addresses depending on the SA

port configuration, 0x40 or 0100000x when SA = 0, and 0x42 or 0100001x when SA = 1.

The 8th bit (LSB) identifies read or write operation RW, this bit is set to 1 in read mode and 0

for write mode. After a START condition, the STA309B identifies on the bus the device

address and if a match is found, it acknowledges the identification on the SDA bus during

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