X9268 datasheet(7/22 Pages) RENESAS

7 / 22 page

X9268

FN8172 Rev.4.00

Page 7 of 22

August 29, 2006

SERIAL INTERFACE DESCRIPTION

Serial Interface

The X9268 supports a bidirectional bus oriented

protocol. The protocol defines any device that sends

data onto the bus as a transmitter and the receiving

device as the receiver. The device controlling the

transfer is a master and the device being controlled is

the slave. The master will always initiate data transfers

and provide the clock for both transmit and receive

operations. Therefore, the X9268 will be considered a

slave device in all applications.

Clock and Data Conventions

Data states on the SDA line can change only during SCL

LOW periods. SDA state changes during SCL HIGH are

reserved for indicating start and stop conditions. See

Figure 2.

Start Condition

All commands to the X9268 are preceded by the start

condition, which is a HIGH to LOW transition of SDA

while SCL is HIGH. The X9268 continuously monitors

the SDA and SCL lines for the start condition and will not

respond to any command until this condition is met. See

Figure 2.

Stop Condition

All communications must be terminated by a stop

condition, which is a LOW to HIGH transition of SDA

while SCL is HIGH. See Figure 2.

Acknowledge

Acknowledge is a software convention used to provide a

positive handshake between the master and slave

devices on the bus to indicate the successful receipt of

data. The transmitting device, either the master or the

slave, will release the SDA bus after transmitting eight

bits. The master generates a ninth clock cycle and

during this period the receiver pulls the SDA line LOW to

acknowledge that it successfully received the eight bits

of data.

The X9268 will respond with an acknowledge after

recognition of a start condition and its slave address and

once again after successful receipt of the command

byte. If the command is followed by a data byte the

X9268 will respond with a final acknowledge. See Figure

Figure 2. Acknowledge Response from Receiver

SCL FROM

MASTER

DATA

OUTPUT

FROM

TRANSMITTER

DATA

OUTPUT

FROM

RECEIVER

START

ACKNOWLEDGE

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