1337CSRI datasheet(9/24 Pages) IDT

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IDT1337

REA LTIME CLOCK WITH SERIAL INTERFACE

RTC

IDT™ REAL-TIME CLOCK WITH I2C SERIAL INTERFACE

IDT1337

REV J 111009

I2C Serial Data Bus

The IDT1337 supports the I2C bus protocol. A device that

sends data onto the bus is defined as a transmitter and a

device receiving data as a receiver. The device that controls

the message is called a master. The devices that are

controlled by the master are referred to as slaves. A master

device that generates the serial clock (SCL), controls the

bus access, and generates the START and STOP conditions

must control the bus. The IDT1337 operates as a slave on

the I2C bus. Within the bus specifications, a standard mode

(100 kHz maximum clock rate) and a fast mode (400 kHz

maximum clock rate) are defined. The IDT1337 works in

both modes. Connections to the bus are made via the

open-drain I/O lines SDA and SCL.

The following bus protocol has been defined (see the “Data

Transfer on I2C Serial Bus” figure):

• Data transfer may be initiated only when the bus is not

busy.

• During data transfer, the data line must remain stable

whenever the clock line is HIGH. Changes in the data line

while the clock line is HIGH are interpreted as control

signals.

Accordingly, the following bus conditions have been defined:

Bus not busy: Both data and clock lines remain HIGH.

Start data transfer: A change in the state of the data line,

from HIGH to LOW, while the clock is HIGH, defines a

START condition.

Stop data transfer: A change in the state of the data line,

from LOW to HIGH, while the clock line is HIGH, defines the

STOP condition.

Data valid: The state of the data line represents valid data

when, after a START condition, the data line is stable for the

duration of the HIGH period of the clock signal. The data on

the line must be changed during the LOW period of the clock

signal. There is one clock pulse per bit of data.

Each data transfer is initiated with a START condition and

terminated with a STOP condition. The number of data

bytes transferred between START and STOP conditions are

not limited, and are determined by the master device. The

information is transferred byte-wise and each receiver

acknowledges with a ninth bit.

Acknowledge: Each receiving device, when addressed, is

obliged to generate an acknowledge after the reception of

each byte. The master device must generate an extra clock

pulse that is associated with this acknowledge bit.

A device that acknowledges must pull down the SDA line

during the acknowledge clock pulse in such a way that the

SDA line is stable LOW during the HIGH period of the

acknowledge related clock pulse. Of course, setup and hold

times must be taken into account. A master must signal an

end of data to the slave by not generating an acknowledge

bit on the last byte that has been clocked out of the slave. In

this case, the slave must leave the data line HIGH to enable

the master to generate the STOP condition.

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