1996 Nov 21
12
Philips Semiconductors
Product specification
DTMF/modem/musical-tone generators
PCD3311C; PCD3312C
8.3
System configuration
(see Fig.9)
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
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.9 System configuration.
MBA605
MASTER
TRANSMITTER /
RECEIVER
SLAVE
RECEIVER
SLAVE
TRANSMITTER /
RECEIVER
MASTER
TRANSMITTER
MASTER
TRANSMITTER /
RECEIVER
SDA
SCL
Fig.10 Acknowledgment on the I
2
C-bus.
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