I
2
C Interface
27-8
Freescale Semiconductor
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
Figure 27-7. I
2
C Standard Communication Protocol
27.3.2
Slave Address Transmission
The master sends the slave address in the first byte after the START signal (B). After the seven-bit calling
address, it sends the R/W bit (C), which tells the slave data transfer direction (0 equals write transfer, 1
equals read transfer).
Each slave must have a unique address. An I
2
C master must not transmit its own slave address; it cannot
be master and slave at the same time.
The slave whose address matches that sent by the master pulls I2C_SDA low at the ninth serial clock (D)
to return an acknowledge bit.
27.3.3
Data Transfer
When successful slave addressing is achieved, data transfer can proceed (see E in
byte-by-byte basis in the direction specified by the R/W bit sent by the calling master.
Data can be changed only while I2C_SCL is low and must be held stable while I2C_SCL is high, as
shows. I2C_SCL is pulsed once for each data bit, with the msb being sent first. The receiving
device must acknowledge each byte by pulling I2C_SDA low at the ninth clock; therefore, a data byte
transfer takes nine clock pulses. See
Figure 27-8. Data Transfer
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
9 9
AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W
XXX
D7
D6
D5
D4
D3
D2
D1
D0
Calling Address
R/W
ACK
Bit
Data Byte
No
ACK
Bit
STOP
Signal
lsb
msb
lsb
msb
START
Signal
A
B
D
C
E
F
Interrupt bit set
(Byte complete)
I2C_SCL
I2C_SDA
I2C_
SCL held low while
Interrupt is serviced
1
2
3
4
5
6
7
8
9
5
6
7
8
4
3
2
1
Bit6
Bit4
Bit3
Bit2
Bit1
Bit5
Bit7
Bit0
Bit6
Bit4
Bit3
Bit2
Bit1
Bit5
Bit0
Bit7
START
Signal
ACK from
Receiver
STOP
No
ACK Bit
Data Byte
Slave Address
R/W
Signal
Interrupt Bit Set
(Byte Complete)
9
I2C_SCL
I2C_SDA
I2C_
SCL held low while
Interrupt is serviced
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60
