MC9S08DN60_08 Datasheet, PDF (204/356 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 11 Inter-Integrated Circuit (S08IICV2)
msb
lsb
SCL
1 2 34 5 6 78 9
msb
lsb
1 2 34 5 6 78 9
SDA
AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W
XXX D7 D6 D5 D4 D3 D2 D1 D0
Start
Signal
Calling Address
Read/ Ack
Write ^Bit
msb
lsb
SCL
1 2 34 5 67 89
Data Byte
No Stop
Ack Signal
Bit
msb
lsb
1 234 5 678 9
SDA
AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W
XX
AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W
Start
Signal
Calling Address
Read/ Ack
Write ^Bit
Repeated
Start
Signal
New Calling Address
Figure 11-9. IIC Bus Transmission Signals
Read/ No Stop
Write
Ack Signal
Bit
11.4.1.1 Start Signal
When the bus is free, no master device is engaging the bus (SCL and SDA lines are at logical high), a
master may initiate communication by sending a start signal. As shown in Figure 11-9, 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.
11.4.1.2 Slave Address Transmission
The first byte of data transferred immediately after the start signal is the slave address transmitted by the
master. This is a seven-bit calling address followed by a R/W bit. The R/W bit tells the slave the desired
direction of data transfer.
1 = Read transfer, the slave transmits data to the master.
0 = Write transfer, the master transmits data to the slave.
Only the slave with a calling address that matches the one transmitted by the master responds by sending
back an acknowledge bit. This is done by pulling the SDA low at the ninth clock (see Figure 11-9).
No two slaves in the system may have the same address. If the IIC module is the master, it must not transmit
an address equal to its own slave address. The IIC cannot be master and slave at the same time. However,
if arbitration is lost during an address cycle, the IIC reverts to slave mode and operates correctly even if it
is being addressed by another master.
MC9S08DN60 Series Data Sheet, Rev 3
204
Freescale Semiconductor