LNBH24PPR datasheet(14/30 Pages) STMICROELECTRONICS

14 / 30 page

I²C bus interface

LNBH24

14/30

I²C bus interface

Data transmission from main MCU to the LNBH24 and vice-versa takes place through the 2

wires I2C bus Interface, consisting of the 2 SDA and SCL lines (pull-up resistors to positive

supply voltage must be externally connected).

6.1

Data validity

As shown in Figure 5 the data on the SDA line must be stable during the high semi-period of

the clock. The HIGH and LOW state of the data line can only change when the clock signal

on the SCL line is LOW.

6.2

Start and stop condition

As shown in Figure 6 a start condition is a HIGH to LOW transition of the SDA line while

SCL is HIGH. The stop condition is a LOW to HIGH transition of the SDA line while SCL is

HIGH. A STOP condition must be sent before each START condition.

6.3

Byte format

Every byte transferred to the SDA line must contain 8 bits. Each byte must be followed by an

acknowledge bit. The MSB is transferred first.

6.4

Acknowledge

The master (MCU) puts a resistive HIGH level on the SDA line during the acknowledge clock

pulse (see Figure 7). The peripheral (LNBH24) that acknowledges has to pull-down (LOW)

the SDA line during the acknowledge clock pulse, so that the SDA line is stable LOW during

this clock pulse. The peripheral which has been addressed has to generate acknowledge

after the reception of each byte, otherwise the SDA line remains at the HIGH level during the

ninth clock pulse time. In this case the master transmitter can generate the STOP

information in order to abort the transfer. The LNBH24 will not generate acknowledge if the

VCC supply is below the under-voltage lockout threshold (6.7 V typ.).

6.5

Transmission without acknowledge

Avoiding to detect the acknowledges of the LNBH24, the MCU can use a simpler

transmission: simply it waits one clock without checking the slave acknowledging, and sends

the new data. This approach of course is less protected from malfunctions and decreases

the noise immunity.

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