PCA9675
NXP Semiconductors
Remote 16-bit I/O expander for Fm+ I2C-bus with interrupt
SDA
SCL
SLAVE
TRANSMITTER/
RECEIVER
MASTER
TRANSMITTER/
RECEIVER
MASTER
TRANSMITTER/
RECEIVER
2
SLAVE
RECEIVER
MASTER
TRANSMITTER
I C-BUS
MULTIPLEXER
SLAVE
002aaa966
Fig 20. System configuration
9.3 Acknowledge
The number of data bytes transferred between the START and the STOP conditions from
transmitter to receiver is not limited. Each byte of eight bits is followed by one
acknowledge bit. The acknowledge bit is a HIGH level put on the bus by the transmitter,
whereas the master generates an extra acknowledge related clock pulse.
A slave receiver which is addressed must generate an acknowledge after the reception of
each byte. Also a master must generate an acknowledge after the reception of each byte
that has been clocked out of the slave transmitter. The device that acknowledges has to
pull down the SDA line during the acknowledge clock pulse, so that the SDA line is stable
LOW during the HIGH period of the acknowledge related clock pulse; set-up and hold
times must be taken into account.
A master receiver must signal an end of data to the transmitter by not generating an
acknowledge on the last byte that has been clocked out of the slave. In this event, the
transmitter must leave the data line HIGH to enable the master to generate a STOP
condition.
data output
by transmitter
not acknowledge
data output
by receiver
acknowledge
SCL from master
1
2
8
9
S
clock pulse for
START
condition
acknowledgement
002aaa987
Fig 21. Acknowledgement on the I2C-bus
PCA9675
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© NXP B.V. 2011. All rights reserved.
Product data sheet
Rev. 2 — 3 October 2011
18 of 34
NXP [ NXP ]
