5

Device operation

The device supports the I2C protocol. This is summarized in Figure 5. Any device that sends data on to the bus

is defined to be a transmitter, and any device that reads the data is defined to be a receiver. The device that

controls the data transfer is known as the bus master, and the other as the slave device. A data transfer can only

be initiated by the bus master, which will also provide the serial clock for synchronization. The device is always a

slave in all communications.

Figure 5. I2C bus protocol

SCL

SDA

SCL

SDA

SDA

START

Condition

SDA

Input

SDA

Change

STOP

Condition

1

2

3

7

8

9

MSB

ACK

START

Condition

SCL

1

2

3

7

8

9

MSB

ACK

STOP

Condition

5.1

Start condition

Start is identified by a falling edge of serial data (SDA) while serial clock (SCL) is stable in the high state. A start

condition must precede any data transfer instruction. The device continuously monitors (except during a Write

cycle) serial data (SDA) and serial clock (SCL) for a start condition.

5.2

Stop condition

Stop is identified by a rising edge of serial data (SDA) while serial clock (SCL) is stable in the high state. A Stop

condition terminates communication between the device and the bus master. A Read instruction is terminated by

no ACK followed by a stop condition to force the device into the standby mode.

A stop condition at the end of a write instruction triggers the internal write cycle.

M24256E-F

Device operation

DS12687 - Rev 3

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