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• Data valid—The state of the data line represents valid data when, after a Start
event, the data line is stable for the duration of the high period of the clock
signal. The data on the line may be changed during the low period of the clock
signal. There is one clock pulse per bit of data.
SDA
SCL
S
Start Event
Each 8-bit word is followed by one acknowledge bit. This acknowledge bit is a high
level put on the bus by the transmitter when the master device generates an extra
acknowledge-related clock pulse. A slave receiver that is addressed is obliged to
generate an acknowledge after the reception of each byte. Also, a master receiver
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 in such a way that the SDA line is stable low
during the high period of the acknowledge-related clock pulse (see Figure 5-9).
Start
Event
SCL From
Master Device
Data Output
by Transmitter
S
Data Output
by Receiver
By definition, a device that generates a signal is called a "transmitter," and the device
that receives the signal is called a "receiver." The device that controls the signal is
called the "master" and the devices that are controlled by the master are called
"slaves". A master receiver must signal an end-of-data to the slave transmitter by not
generating an acknowledge on the last byte that has been clocked out of the slave
device. In this case the transmitter must leave the data line high to enable the master
MOTOROLA
2
Figure 5-8 I
C Start and Stop Events
1
Figure 5-9 Acknowledgment on the I
DSP56012 User's Manual
Characteristics Of The I
2
2
C Bus
Serial Host Interface
2
C Bus
P
Stop Event
AA0423
Clock Pulse For
Acknowledgment
8
9
AA0424
5-21
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