DS1307 Datasheet, PDF (11/14 Pages) Dallas Semiconductor – 64 X 8 Serial Real Time Clock

Figure 3. Data Transfer on I²C Serial Bus
DS1307 64 x 8, Serial, I²C Real-Time Clock
SDA
MSB
R/W
DIRECTION
BIT
ACKNOWLEDGEMENT
SIGNAL FROM RECEIVER
ACKNOWLEDGEMENT
SIGNAL FROM RECEIVER
SCL
START
CONDITION
1
2
6
7
8
9
ACK
1
2
3-7
8
9
ACK
REPEATED IF MORE BYTES
ARE TRANSFERED
STOP
CONDITION
OR
REPEATED
START
CONDITION
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.
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