
Multi-Master IIC Interface (MMIIC)
Multi-Master IIC Bus Protocol
MC68HC908SR12MC68HC08SR12 — Rev. 5.0
Data Sheet
Freescale Semiconductor
Multi-Master IIC Interface (MMIIC)
297
If the master receiver does not acknowledge the slave transmitter after
a byte has been transmitted, it means an “end of data” to the slave. The
slave should release the SDA line for the master to generate a STOP or
START signal.
17.6.4 Repeated START Signal
As shown in
Figure 17-2
, a repeated START signal is used to generate
START signal without first generating a STOP to terminate the
communication. This is used by the master to communicate with another
slave or with the same slave in a different mode (transmit/receive mode)
without releasing the bus.
17.6.5 STOP Signal
The master can terminate the communication by generating a STOP
signal to free the bus. However, the master may generate a START
signal followed by a calling command without first generating a STOP
signal. This is called repeat START. A STOP signal is defined as a low
to high transition of SDA while SCL is at logic high (see
Figure 17-2
).
17.6.6 Arbitration Procedure
The interface circuit is a multi-master system which allows more than
one master to be connected. If two or more masters try to control the bus
at the same time, a clock synchronization procedure determines the bus
clock. The clock low period is equal to the longest clock low period and
the clock high period is equal to the shortest one among the masters. A
data arbitration procedure determines the priority. A master will lose
arbitration if it transmits a logic 1 while another transmits a logic 0. The
losing master will immediately switch over to slave receive mode and
stops its data and clock outputs. The transition from master to slave will
not generate a STOP condition. Meanwhile a software bit will be set by
hardware to indicates loss of arbitration.