1996 Dec 20

10

Philips Semiconductors

Product specification

Analog voice scrambler/descrambler

PCD4440T

8.3

System configuration (see Fig.8)

A device generating a message is a ‘transmitter’, a device receiving a message is the ‘receiver’. The device that controls

message transfer is the ‘master’ and the devices that are controlled by the master are the ‘slaves’.

8.4

Acknowledge (see Fig.9)

The number of data bytes transferred between the start and 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 after the reception of each byte. Also a master must

generate an acknowledge after 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-related clock pulse. Set-up and hold times must

be taken into account to ensure that the SDA line is stable LOW during the whole high period of the acknowledge-related

clock pulse. 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 the stop condition.

Fig.8 System configuration.

MBA605

MASTER

TRANSMITTER /

RECEIVER

SLAVE

RECEIVER

SLAVE

TRANSMITTER /

RECEIVER

MASTER

TRANSMITTER

MASTER

TRANSMITTER /

RECEIVER

SDA

SCL

MBC602

S

START

CONDITION

9

8

2

1

clock pulse for

acknowledgement

not acknowledge

acknowledge

DATA OUTPUT

BY TRANSMITTER

DATA OUTPUT

BY RECEIVER

SCL FROM

MASTER