Datasheet

SCL
SDA
START or
Repeated
START
S or Sr 1
2
7 8 9
MSB
ACK
Acknowledgement
signal from slave
1
2
8 9
ACK
Acknowledgement
signal from receiver
STOP or
Repeated
START
P or Sr
START (S)
STOP (P)
SDA
SCL
SDA
SCL
SDA
SCL
Data line stable;
Data valid
Change
of data
allowed
bq24195
bq24195L
SLUSB97 –OCTOBER 2012 www.ti.com
Figure 23. Bit Transfer on the I
2
C Bus
START and STOP Conditions
All transactions begin with a START (S) and can be terminated by a STOP (P). A HIGH to LOW transition on the
SDA line while SCl is HIGH defines a START condition. A LOW to HIGH transition on the SDA line when the
SCL is HIGH defines a STOP condition.
START and STOP conditions are always generated by the master. The bus is considered busy after the START
condition, and free after the STOP condition.
Figure 24. START and STOP conditions
Byte Format
Every byte on the SDA line must be 8 bits long. The number of bytes to be transmitted per transfer is
unrestricted. Each byte has to be followed by an Acknowledge bit. Data is transferred with the Most Significant
Bit (MSB) first. If a slave cannot receive or transmit another complete byte of data until it has performed some
other function, it can hold the clock line SCL low to force the master into a wait state (clock stretching). Data
transfer then continues when the slave is ready for another byte of data and release the clock line SCL.
Figure 25. Data Transfer on the I
2
C Bus
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