STA538B datasheet(33/59 Pages) STMICROELECTRONICS

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STA538

I2C interface

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I2C interface

This section describes the communication protocol of the I2C interface.

9.1

Data transition and change

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

while the clock is high is used to identify a start or stop condition.

9.2

Start condition

A start condition 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.

9.3

Stop condition

A stop condition 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 STA538 and the master bus.

9.4

Data input

During data input, the STA538 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.

9.5

Device addressing

To start communication between the master and the STA538, the master must initiate with a

start condition. Following this, the master sends onto the SDA line 8 bits (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 STA538, the I2C interface has the device address 0x34.

The 8th bit (LSB) identifies read or write operation (R/W), this bit is set to 1 in read mode

and 0 in write mode. After a start condition, the STA538 identifies on the bus the device

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

9th bit time. The byte following the device identification byte is the internal space address.

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