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Mini57
Apr. 06, 2017
Page 386 of 475
Rev.1.00
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6.14.5.2 START or Repeated START Signal
Figure 6.14-3 shows the typical I
2
C protocol. Normally, a standard communication consists of four
parts:
START or Repeated START signal generation
Slave address and R/W bit transfer
Data transfer
STOP signal generation
SDA
SCL
1-7
8
9
S
1-7
8
9
1-7
8
9
P
ADDRESS
W/R
ACK
DATA
ACK
DATA
ACK
Figure 6.14-3 I
2
C Protocol
When the bus is free/idle, meaning no master device is engaging the bus (both SCL and SDA
lines are high), a master can initiate a transfer by sending a START signal. A START signal,
usually referred to as the “S” bit, is defined as a HIGH to LOW transition on the SDA line while
SCL is HIGH. The START signal denotes the beginning of a new data transmission.
A Repeated START is not a STOP signal between two START signals and usually referred to as
the “Sr” bit. The master uses this method to communicate with another slave or the same slave in
a different transfer direction (e.g. from writing to a device to reading from a device) without
releasing the bus idle flag.
6.14.5.3 STOP Signal
The master can terminate the communication by generating a STOP signal. A STOP signal,
usually referred to as the “P” bit, is defined as a LOW to HIGH transition on the SDA line while
SCL is HIGH. The section between STOP and START is called bus free. Figure 6.14-4 shows the
waveform of START, Repeat START and STOP.
STOP
SDA
SCL
START
Repeated
START
START
STOP
Figure 6.14-4 START and STOP Conditions