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2
Accordingly, the I
C bus protocol defines the following events:
• Bus not busy—Both data and clock lines remain high.
• Start data transfer—The Start event is defined as a change in the state of the
data line, from high to low, while the clock is high (see Figure 5-8).
• Stop data transfer—The Stop event is defined as a change in the state of the
data line, from low to high, while the clock is high (see Figure 5-8).
•
SDA
SCL
S
Start Event
• 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.
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).
MOTOROLA
2
Figure 5-8 I
C Start and Stop Events
DSP56009 User's Manual
Serial Host Interface
Characteristics Of The I
P
Stop Event
2
C Bus
AA0423
5-21
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