8574A View Datasheet(PDF) - Philips Electronics

Part Name

Description

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8574A

Remote 8-bit I/O expander for I2C-BUS

Philips Electronics 

Philips Semiconductors

Remote 8-bit I/O expander for I2C-bus

Product specification

PCF8574

6.4 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 (see Fig.8). 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.

handbook, full pagewidth

DATA OUTPUT

BY TRANSMITTER

DATA OUTPUT

BY RECEIVER

not acknowledge

acknowledge

SCL FROM

MASTER

1

2

S

START

condition

8

9

clock pulse for

acknowledgement

MBC602

Fig.8 Acknowledgment on the I2C-bus.

2002 Nov 22

8

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