mc9s12xd256 Freescale Semiconductor, Inc, mc9s12xd256 Datasheet - Page 411

• Manufacturer Part Number: mc9s12xd256
• Description: Hcs12x Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

If the master receiver does not acknowledge the slave transmitter after a byte transmission, it means 'end
of data' to the slave, so the slave releases the SDA line for the master to generate STOP or START signal.
9.4.1.4
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 generating a STOP signal
first. This is called repeated START. A STOP signal is defined as a low-to-high transition of SDA while
SCL at logical 1 (see
The master can generate a STOP even if the slave has generated an acknowledge at which point the slave
must release the bus.
9.4.1.5
As shown in
STOP signal to terminate the communication. This is used by the master to communicate with another
slave or with the same slave in different mode (transmit/receive mode) without releasing the bus.
9.4.1.6
The Inter-IC bus is a true multi-master 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, 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. The relative priority of the contending masters is determined by a data
arbitration procedure, a bus master loses arbitration if it transmits logic 1 while another master transmits
logic 0. The losing masters immediately switch over to slave receive mode and stop driving SDA output.
In this case the transition from master to slave mode does not generate a STOP condition. Meanwhile, a
status bit is set by hardware to indicate loss of arbitration.
9.4.1.7
Because wire-AND logic is performed on SCL line, a high-to-low transition on SCL line affects all the
devices connected on the bus. The devices start counting their low period and as soon as a device's clock
has gone low, it holds the SCL line low until the clock high state is reached.However, the change of low to
high in this device clock may not change the state of the SCL line if another device clock is within its low
period. Therefore, synchronized clock SCL is held low by the device with the longest low period. Devices
with shorter low periods enter a high wait state during this time (see
concerned have counted off their low period, the synchronized clock SCL line is released and pulled high.
There is then no difference between the device clocks and the state of the SCL line and all the devices start
counting their high periods.The first device to complete its high period pulls the SCL line low again.
Freescale Semiconductor
Figure
STOP Signal
Repeated START Signal
Arbitration Procedure
Clock Synchronization
9-9, a repeated START signal is a START signal generated without first generating a
Figure
9-9).
MC9S12XDP512 Data Sheet, Rev. 2.17
Chapter 9 Inter-Integrated Circuit (IICV2) Block Description
Figure
9-10). When all devices
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