Datasheet

SDA
SCL
S P
Start Condition
Stop Condition
SDA
SCL
Data Line Change
Data Output
by Transmitter
SCL From
Master
Start
Condition
S
1 2 8 9
Data Output
by Receiver
Clock Pulse for
Acknowledgment
NACK
ACK
PCA9557
SCPS133I – DECEMBER 2005 – REVISED JUNE 2008 .................................................................................................................................................... www.ti.com
A master receiver signals an end of data to the slave transmitter by not generating an acknowledge (NACK) after
the last byte has been clocked out of the slave. This is done by the master receiver by holding the SDA line high.
In this event, the transmitter must release the data line to enable the master to generate a stop condition.
Figure 1. Definition of Start and Stop Conditions
Figure 2. Bit Transfer
Figure 3. Acknowledgment on the I
2
C Bus
Interface Definition
BIT
BYTE
7 (MSB) 6 5 4 3 2 1 0 (LSB)
I
2
C slave address L L H H A2 A1 A0 R/ W
Px I/O data bus P7 P6 P5 P4 P3 P2 P1 P0
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