MC68HC705E5 Datasheet, PDF (76/148 Pages) Freescale Semiconductor, Inc – General Release Specification

Freescale Semiconductor, Inc.
Motorola Bus (M Bus) Interface
11.5.4 Repeated Start Signal
As shown in Figure 11-1, a repeated start signal is used to generate a
start signal without first generating a stop signal 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.
11.5.5 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 logical high. (See Figure 11-1.)
11.5.6 Arbitration Procedure
This interface circuit is a true multimaster system which allows more
than one master to be connected to it. If two or more masters try to
control the bus at the same time, a clock synchronization procedure
determines the bus clock, for which the low period is equal to the longest
clock low period and the high is equal to the shortest one among the
masters. A data arbitration procedure determines the priority. The
masters will lose arbitration if they transmit a logic 1 while another
transmits logic 0. The losing masters will immediately switch over to
slave receive mode and stop its data and clock outputs. In this case, the
transition from master to slave mode will not generate a stop condition;
however, a software bit will be set by hardware to indicate loss of
arbitration.
General Release Specification
Motorola Bus (M Bus) Interface
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MC68HC705E5 — Rev. 1.0