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MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 25-11
Figure 25-10. Repeated START
Various combinations of read/write formats are then possible:
• The first example in Figure 25-11 is the case of master-transmitter transmitting to slave-receiver.
The transfer direction is not changed.
• The second example in Figure 25-11 is the master reading the slave immediately after the first byte.
At the moment of the first acknowledge, the master-transmitter becomes a master-receiver and the
slave-receiver becomes slave-transmitter.
• In the third example in Figure 25-11, START condition and slave address are repeated using the
repeated START signal. This is to communicate with same slave in a different mode without
releasing the bus. The master transmits data to the slave first, and then the master reads data from
slave by reversing the R/W bit.
Figure 25-11. Data Transfer, Combined Format
12345678 12 5 67834
AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W AD7 AD6 AD5 AD4 AD3 AD2 AD1 R/W
99
XX
New Calling Address
R/W
No
ACK
Bit
STOP
Signal
Repeated
START
Signal
ACK
Bit
R/W
Calling Address
START
msb lsb
msb
lsb
Signal
A
SCL
SDA
ST
A
7bit Slave Address
0
A
Data
Data A/A
R/W
SP
From Master to Slave
From Slave to Master
ST
A
7bit Slave Address
1
A
Data
A
R/W
SP
ST
A
1
A
Data
R/W
Rept
A
7-bit Slave
0
A
Data
Data
A/A
R/W
SP
ST
Address
7-bit Slave
Address
Example 1:
Example 2:
Example 3:
Master Reads from Slave
Master Writes to Slave
Note: No acknowledge on the last byte
Data
ST = Start
SP = Stop
A = Acknowledge (SDA low)
A
= Not Acknowledge (SDA high)
Rept ST = Repeated Start