I
2
C Interface
MCF5213 ColdFire® Integrated Microcontroller Reference Manual, Rev. 3
Freescale Semiconductor
22-9
22.3.4
Acknowledge
The transmitter releases the I2C_SDA line high during the acknowledge clock pulse as shown in
. The receiver pulls down the I2C_SDA line during the acknowledge clock pulse so that it
remains stable low during the high period of the clock pulse.
If it does not acknowledge the master, slave receiver must leave I2C_SDA high. The master can then
generate a STOP signal to abort data transfer or generate a START signal (repeated start, shown in
Section 22.3.6, “Repeated START”
) to start a new calling sequence.
Figure 22-9. Acknowledgement by Receiver
If the master receiver does not acknowledge the slave transmitter after a byte transmission, it means
end-of-data to the slave. The slave releases I2C_SDA for the master to generate a STOP or START signal
(
).
22.3.5
STOP Signal
The master can terminate communication by generating a STOP signal to free the bus. A STOP signal is
defined as a low-to-high transition of I2C_SDA while I2C_SCL is at logical high (see F in
).
The master can generate a STOP even if the slave has generated an acknowledgment, at which point the
slave must release the bus. The master may also generate a START signal following a calling address,
without first generating a STOP signal. Refer to
Section 22.3.6, “Repeated START.”
22.3.6
Repeated START
A repeated START signal is a START signal generated without first generating a STOP signal to terminate
the communication. The master uses a repeated START to communicate with another slave or with the
same slave in a different mode (transmit/receive mode) without releasing the bus.
5
6
7
8
9
I2C_SCL
4
3
2
1
Bit6
Bit4 Bit3 Bit2 Bit1
Bit5
I2C_SDA by Transmitter
Bit7
Bit0
START Signal
R/W
I2C_SDA by Receiver
ACK
