DS1307 64 x 8, Serial, I

2C Real-Time Clock

11 of 14

Figure 3. Data Transfer on I2C Serial Bus

Depending upon the state of the R/

W bit, two types of data transfer are possible:

1. Data transfer from a master transmitter to a slave receiver. The first byte transmitted by the master is the

slave address. Next follows a number of data bytes. The slave returns an acknowledge bit after each received

byte. Data is transferred with the most significant bit (MSB) first.

2. Data transfer from a slave transmitter to a master receiver. The first byte (the slave address) is transmitted

by the master. The slave then returns an acknowledge bit. This is followed by the slave transmitting a number

of data bytes. The master returns an acknowledge bit after all received bytes other than the last byte. At the

end of the last received byte, a “not acknowledge” is returned.

The master device generates all the serial clock pulses and the START and STOP conditions. A transfer is

ended with a STOP condition or with a repeated START condition. Since a repeated START condition is also

the beginning of the next serial transfer, the bus will not be released. Data is transferred with the most

significant bit (MSB) first.

ACKNOWLEDGEMENT

SIGNAL FROM RECEIVER

ACKNOWLEDGEMENT

SIGNAL FROM RECEIVER

R/

W

DIRECTION

BIT

REPEATED IF MORE BYTES

ARE TRANSFERED

START

CONDITION

STOP

CONDITION

OR

REPEATED

START

CONDITION

MSB

1

2

6

7

8

9

1

2

3-7

8

9

ACK

ACK

SDA

SCL