MC9S08DZ96F2CLL datasheet(244/458 Pages) FREESCALE

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Chapter 11 Inter-Integrated Circuit (S08IICV2)

MC9S08DZ128 Series Data Sheet, Rev. 1

244

Freescale Semiconductor

Figure 11-9. IIC Bus Transmission Signals

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.

SCL

SDA

Start

Signal

Ack

Bit

4567

msb

lsb

4567

msb

lsb

Stop

Signal

SCL

SDA

456

msb

lsb

msb

lsb

Repeated

AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W

XXX

Calling Address

Read/

Data Byte

AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W

New Calling Address

Ack

Bit

Write

Start

Signal

Start

Signal

Ack

Bit

Calling Address

Read/

Write

Stop

Signal

Ack

Bit

Read/

Write

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