TCA9554A Datasheet, PDF (6/33 Pages) Texas Instruments – LOW VOLTAGE 8-BIT I2C AND SMBus I/O EXPANDER

TCA9554A
SCPS196 – DECEMBER 2010
www.ti.com
A Stop condition, a low-to-high transition on the SDA input/output while the SCL input is high, is sent by the
master (see Figure 1).
Any number of data bytes can be transferred from the transmitter to receiver between the Start and 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 (see
Figure 3). 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 will signal 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 Output
by Receiver
Data Line
Stable;
Data Valid
Change
of Data
Allowed
Figure 2. Bit Transfer
NACK
ACK
SCL From
Master
S
Start
Condition
1
2
8
Figure 3. Acknowledgment on the I²C Bus
9
Clock Pulse for
Acknowledgment
6
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