I2C Protocol - NXP Semiconductors MC9S08SU16 Reference Manual

21.5.1 I2C protocol

The I2C bus system uses a serial data line (SDA) and a serial clock line (SCL) for data
transfers.
All devices connected to it must have open drain or open collector outputs. A logic AND
function is exercised on both lines with external pull-up resistors. The value of these
resistors depends on the system.
Normally, a standard instance of communication is composed of four parts:
1. START signal
2. Slave address transmission
3. Data transfer
4. STOP signal
The STOP signal should not be confused with the CPU STOP instruction. The following
figure illustrates I2C bus system communication.
MSB
SCL 1 2
SDA AD6 AD5
AD7
Calling Address
Start
Signal
MSB
SCL
1 2
SDA
AD7 AD6 AD5
Calling Address
Start
Signal
NXP Semiconductors
LSB
3 4 5 6
7 8
AD4
AD3 AD2 AD1 R/W
Read/
Ack
Write Bit
LSB
3 4
5 6 7 8
AD4 AD3 AD2 AD1 R/W
Read/
Ack
Bit
Write
Figure 21-2. I2C bus transmission signals
MC9S08SU16 Reference Manual, Rev. 5, 4/2017
Chapter 21 Inter-Integrated Circuit (I2C)
MSB
1 2 3
9
XXX D7 D6 D5
Data Byte
MSB
1 2 3
9
XX AD7 AD6 AD5 AD4
Repeated New Calling Address
Start
Signal
LSB
4 5 6
7 8 9
D4 D3 D2 D1 D0
No Stop
Signal
Ack
Bit
LSB
4
5 6 7 8 9
AD3 AD2 AD1 R/W
No
Stop
Read/
Ack
Signal
Write
Bit
377