Datasheet

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.
Figures 3 and 4 detail how data transfer is accom-
plished on the I
2
C bus. Depending upon the state of
the R/W bit, two types of data transfer are possible:
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.
Data transfer from a slave transmitter to a master
receiver. The first byte (the slave address) is trans-
mitted by the master. The slave then returns an
acknowledge bit. Next follows a number of data
bytes transmitted by the slave to the master. The
Extremely Accurate I
2
C-Integrated
RTC/TCXO/Crystal
SDA
SCL
IDLE
1–7 8 9 1–7 8 9 1–7 8 9
START
CONDITION
STOP CONDITION
REPEATED START
SLAVE
ADDRESS
R/W ACK ACKDATA ACK/
NACK
DATA
MSB FIRST MSB LSB MSB LSB
REPEATED IF MORE BYTES
ARE TRANSFERRED
Figure 2. I
2
C Data Transfer Overview
...
AXXXXXXXXA1101000S 0 XXXXXXXX A XXXXXXXX A XXXXXXXX A P
<R/W> <WORD ADDRESS (n)> <DATA (n)> <DATA (n + 1)> <DATA (n + X)
S - START
A - ACKNOWLEDGE (ACK)
P - STOP
R/W - READ/WRITE OR DIRECTION BIT ADDRESS
DATA TRANSFERRED
(X + 1 BYTES + ACKNOWLEDGE)
MASTER TO SLAVESLAVE TO MASTER
<SLAVE
ADDRESS>
Figure 3. Data Write—Slave Receiver Mode
...
AXXXXXXXXA1101000S 1 XXXXXXXX A XXXXXXXX A XXXXXXXX A P
S - START
A - ACKNOWLEDGE (ACK)
P - STOP
A - NOT ACKNOWLEDGE (NACK)
R/W - READ/WRITE OR DIRECTION BIT ADDRESS
DATA TRANSFERRED
(X + 1 BYTES + ACKNOWLEDGE)
NOTE: LAST DATA BYTE IS FOLLOWED BY A NACK.
MASTER TO SLAVE SLAVE TO MASTER
<R/W> <DATA (n)> <DATA (n + 1)> <DATA (n + 2)> <DATA (n + X)>
<SLAVE
ADDRESS>
Figure 4. Data Read—Slave Transmitter Mode
DS3231
16
Maxim Integrated