Datasheet

PCA9551_8 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 08 — 31 July 2008 9 of 26
NXP Semiconductors
PCA9551
8-bit I
2
C-bus LED driver with programmable blink rates
7.3 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.
Fig 9. System configuration
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MASTER
TRANSMITTER/
RECEIVER
SLAVE
RECEIVER
SLAVE
TRANSMITTER/
RECEIVER
MASTER
TRANSMITTER
MASTER
TRANSMITTER/
RECEIVER
SDA
SCL
I
2
C-BUS
MULTIPLEXER
SLAVE
Fig 10. Acknowledgement on the I
2
C-bus
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S
START
condition
9821
clock pulse for
acknowledgement
not acknowledge
acknowledge
data output
by transmitter
data output
by receiver
SCL from master