15.3.1.1 START and STOP Conditions
START and STOP conditions are used to initiate and stop transactions on the I
2
C-bus. All transactions on the bus begin with a START
condition (S) and end with a STOP condition (P). As shown in
Figure 15.4 I2C START and STOP Conditions on page 398
, a START
condition is generated by pulling the SDA line low while SCL is high, and a STOP condition is generated by pulling the SDA line high
while SCL is high.
SCL
SDA
S
P
START condition
STOP condition
Figure 15.4. I2C START and STOP Conditions
The START and STOP conditions are easily identifiable bus events as they are the only conditions on the bus where a transition is
allowed on SDA while SCL is high. During the actual data transmission, SDA is only allowed to change while SCL is low, and must be
stable while SCL is high. One bit is transferred per clock pulse on the I
2
C-bus as shown in
Figure 15.5 I2C Bit Transfer on I
.
SCL
SDA
Data stable
Data change
allowed
Data change
allowed
Figure 15.5. I2C Bit Transfer on I
2
C-Bus
EFM32JG1 Reference Manual
I2C - Inter-Integrated Circuit Interface
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