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Functional description
No two slaves in the system can have the same address. If the I2C module is the master, it
must not transmit an address that is equal to its own slave address. The I2C module
cannot be master and slave at the same time. However, if arbitration is lost during an
address cycle, the I2C module reverts to slave mode and operates correctly even if it is
being addressed by another master.
45.5.1.3 Data transfers
When successful slave addressing is achieved, data transfer can proceed on a byte-by-
byte basis in the direction specified by the R/W bit sent by the calling master.
All transfers that follow an address cycle are referred to as data transfers, even if they
carry subaddress information for the slave device.
Each data byte is 8 bits long. Data may be changed only while SCL is low. Data must be
held stable while SCL is high. There is one clock pulse on SCL for each data bit, and the
MSB is transferred first. Each data byte is followed by a ninth (acknowledge) bit, which
is signaled from the receiving device by pulling SDA low at the ninth clock. In summary,
one complete data transfer needs nine clock pulses.
If the slave receiver does not acknowledge the master in the ninth bit, the slave must
leave SDA high. The master interprets the failed acknowledgement as an unsuccessful
data transfer.
If the master receiver does not acknowledge the slave transmitter after a data byte
transmission, the slave interprets it as an end to data transfer and releases the SDA line.
In the case of a failed acknowledgement by either the slave or master, the data transfer is
aborted and the master does one of two things:
• Relinquishes the bus by generating a STOP signal.
• Commences a new call by generating a repeated START signal.
45.5.1.4 STOP signal
The master can terminate the communication by generating a STOP signal to free the
bus. A STOP signal is defined as a low-to-high transition of SDA while SCL is asserted.
The master can generate a STOP signal even if the slave has generated an
acknowledgement, at which point the slave must release the bus.
1248
KV4x Reference Manual, Rev. 2, 02/2015
Preliminary
Freescale Semiconductor, Inc.
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