TCA7408 Datasheet, PDF (5/25 Pages) Texas Instruments – Low-Voltage 8-Bit I2C and SMBus I/O Expander with Interrupt Output, RESET, I/ODirection Registers, and Programmable Pull-up/Pull-down

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TCA7408
SCPS235 – NOVEMBER 2011
A Stop condition, a low-to-high transition on the SDA input/output while the SCL input is high, is sent by the
master.
Any number of data bytes can be transferred from the transmitter to receiver between the Start and the Stop
conditions. Each byte of eight bits is followed by one ACK bit. The transmitter must release the SDA line before
the receiver can send an ACK bit. The device that acknowledges must pull down the SDA line during the ACK
clock pulse, so that the SDA line is stable low during the high pulse of the ACK-related clock period. When a
slave receiver is addressed, it must generate an ACK after each byte is received. Similarly, the master must
generate an ACK after each byte that it receives from the slave transmitter. Setup and hold times must be met to
ensure proper operation.
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.
SDA
SCL
S
P
Start Condition
Stop Condition
Figure 1. Definition of Start and Stop Conditions
SDA
SCL
Data Output
by Transmitter
Data Line Change
Figure 2. Bit Transfer
Data Output
by Receiver
NACK
SCL From
Master
ACK
Start
Condition
Figure 3. Acknowledgment on I²C Bus
Clock Pulse for
Acknowledgment
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