Datasheet

Chapter 9 Inter-Integrated Circuit (IICV2) Block Description
MC9S12XDP512 Data Sheet, Rev. 2.21
Freescale Semiconductor 409
9.4 Functional Description
This section provides a complete functional description of the IICV2.
9.4.1 I-Bus Protocol
The IIC bus system uses a serial data line (SDA) and a serial clock line (SCL) for data transfer. All devices
connected to it must have open drain or open collector outputs. Logic AND function is exercised on both
lines with external pull-up resistors. The value of these resistors is system dependent.
Normally, a standard communication is composed of four parts: START signal, slave address transmission,
data transfer and STOP signal. They are described briefly in the following sections and illustrated in
Figure 9-9.
Figure 9-9. IIC-Bus Transmission Signals
9.4.1.1 START Signal
When the bus is free, i.e. no master device is engaging the bus (both SCL and SDA lines are at logical
high), a master may initiate communication by sending a START signal.As shown in Figure 9-9, a START
signal is defined as a high-to-low transition of SDA while SCL is high. This signal denotes the beginning
of a new data transfer (each data transfer may contain several bytes of data) and brings all slaves out of
their idle states.
SCL
SDA
Start
Signal
Ack
Bit
12345678
MSB LSB
12345678
MSB LSB
Stop
Signal
No
SCL
SDA
12345678
MSB LSB
1 2 5 678
MSB LSB
Repeated
34
99
AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W XXX D7 D6 D5 D4 D3 D2 D1 D0
Calling Address Read/ Data Byte
AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W
New Calling Address
99
XX
Ack
Bit
Write
Start
Signal
Start
Signal
Ack
Bit
Calling Address Read/
Write
Stop
Signal
No
Ack
Bit
Read/
Write