Table of Contents
Advertisement
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.
21.5.1.4 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.
21.5.1.5 Repeated START signal
The master may generate a START signal followed by a calling command without
generating a STOP signal first. This action is called a repeated START. 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.The master needs to
send a NACK signal before sending repeated-START in the buffering mode.
21.5.1.6 Arbitration procedure
The I2C bus is a true multimaster bus that allows more than one master to be connected
on it.
If two or more masters try to control the bus at the same time, a clock synchronization
procedure determines the bus clock. The bus clock's low period is equal to the longest
clock low period, and the high period is equal to the shortest one among the masters.
The relative priority of the contending masters is determined by a data arbitration
procedure. A bus master loses arbitration if it transmits logic level 1 while another master
transmits logic level 0. The losing masters immediately switch to slave receive mode and
NXP Semiconductors
MC9S08SU16 Reference Manual, Rev. 5, 4/2017
Chapter 21 Inter-Integrated Circuit (I2C)
379
Advertisement
Table of Contents
