Philips Semiconductors
Product specification
Remote 8-bit I/O expander for I
2
C-bus
6.4
Acknowledge
PCF8574
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.
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
DATA OUTPUT
BY TRANSMITTER
not acknowledge
DATA OUTPUT
BY RECEIVER
acknowledge
SCL FROM
MASTER
S
START
CONDITION
MBC602
1
2
8
9
clock pulse for
acknowledgement
Fig.7 Acknowledgment on the I
2
C-bus.
1997 Apr 02
7
PHILIPS [ NXP SEMICONDUCTORS ]
