STA321MPL1 datasheet(17/80 Pages) STMICROELECTRONICS

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STA321MPL1

I2C bus operation

The STA321MPL1 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 to the bus as a transmitter and any device

that reads data as a receiver.

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

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

STA321MPL1 is a slave device in all of its communications.

4.1

Communication protocol

4.1.1

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.

4.1.2

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.

4.1.3

Stop condition

STOP is identified by a 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 STA321MPL1 and the bus master.

4.1.4

Data input

During data input, the STA321MPL1 samples the SDA signal on the rising edge of the clock

SCL.

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

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

4.2

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 onto 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 STA321MPL1 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.

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