Device operation

M34D64-W

12/27

3

Device operation

device that sends data on to the bus is defined to be a transmitter, and any device that reads

the data 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 M34D64-W device is

always a slave in all communications.

3.1

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 command. The device

continuously monitors (except during a Write cycle) Serial Data (SDA) and Serial Clock

(SCL) for a Start condition, and will not respond unless one is given.

3.2

Stop condition

Stop is identified by a rising edge of Serial Data (SDA) while Serial Clock (SCL) is stable

and driven high. A Stop condition terminates communication between the device and the

bus master. A Read command that is followed by NoAck can be followed by a Stop condition

to force the device into the Standby mode. A Stop condition at the end of a Write command

triggers the internal EEPROM Write cycle.

3.3

Acknowledge bit (ACK)

The acknowledge bit is used to indicate a successful byte transfer. The bus transmitter,

whether it be bus master or slave device, releases Serial Data (SDA) after sending eight bits

acknowledge the receipt of the eight data bits.

3.4

Data input

During data input, the device samples Serial Data (SDA) on the rising edge of Serial Clock

(SCL). For correct device operation, Serial Data (SDA) must be stable during the rising edge

of Serial Clock (SCL), and the Serial Data (SDA) signal must change only when Serial Clock

(SCL) is driven low.