Datasheet
SDA
SCL
t
HD-STA
0.9 s³ m
t
SU-STO
0.9 s³ m
P
S
t
SU-STA
0.9 s³ m
Sr
t
HD-STA
0.9 s³ m
S
T0114-02
TLV320AIC3105
SLAS513B – FEBRUARY 2007 – REVISED DECEMBER 2008 .........................................................................................................................................
www.ti.com
Figure 14. I
2
C Interface Timing
Communication on the I
2
C bus always takes place between two devices, one acting as the master and the other
acting as the slave. Both masters and slaves can read and write, but slaves can only do so under the direction of
the master. Some I
2
C devices can act as masters or slaves, but the TLV320AIC3105 can only act as a slave
device.
An I
2
C bus consists of two lines, SDA and SCL. SDA carries data; SCL provides the clock. All data is transmitted
across the I
2
C bus in groups of eight bits. To send a bit on the I
2
C bus, the SDA line is driven to the appropriate
level while SCL is LOW (a LOW on SDA indicates the bit is zero; a HIGH indicates the bit is one). Once the SDA
line has settled, the SCL line is brought HIGH, then LOW. This pulse on SCL clocks the SDA bit into the
receivers shift register.
The I
2
C bus is bidirectional: the SDA line is used both for transmitting and receiving data. When a master reads
from a slave, the slave drives the data line; when a master sends to a slave, the master drives the data line.
Under normal circumstances the master drives the clock line.
Most of the time the bus is idle, no communication is taking place, and both lines are HIGH. When
communication is taking place, the bus is active. Only master devices can start a communication. They do this by
causing a START condition on the bus. Normally, the data line is only allowed to change state while the clock
line is LOW. If the data line changes state while the clock line is HIGH, it is either a START condition or its
counterpart, a STOP condition. A START condition is when the clock line is HIGH and the data line goes from
HIGH to LOW. A STOP condition is when the clock line is HIGH and the data line goes from LOW to HIGH.
After the master issues a START condition, it sends a byte that indicates which slave device it wants to
communicate with. This byte is called the address byte. Each device on an I
2
C bus has a unique 7-bit address to
which it responds. (Slaves can also have 10-bit addresses; see the I
2
C specification for details.) The master
sends an address in the address byte, together with a bit that indicates whether it wishes to read from or write to
the slave device.
Every byte transmitted on the I
2
C bus, whether it is address or data, is acknowledged with an acknowledge bit.
When a master has finished sending a byte (eight data bits) to a slave, it stops driving SDA and waits for the
slave to acknowledge the byte. The slave acknowledges the byte by pulling SDA LOW. The master then sends a
clock pulse to clock the acknowledge bit. Similarly, when a master has finished reading a byte, it pulls SDA LOW
to acknowledge this to the slave. It then sends a clock pulse to clock the bit.
A not-acknowledge is performed by simply leaving SDA HIGH during an acknowledge cycle. If a device is not
present on the bus, and the master attempts to address it, it receives a not-acknowledge because no device is
present at that address to pull the line LOW.
When a master has finished communicating with a slave, it may issue a STOP condition. When a STOP
condition is issued, the bus becomes idle again. A master may also issue another START condition. When a
START condition is issued while the bus is active, it is called a repeated START condition.
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