Z51F6412
Product Specification
PS030302-0212
P R E L I M I N A R Y
120
with its LOW period determined by the device with the longest clock LOW period, and its HIGH period
determined by the one with the shortest clock HIGH period.
A master may start a transfer only if the bus is free. Two or more masters may generate a START
condition. Arbitration takes place on the SDA line, while the SCL line is at the HIGH level, in such a
way that the master which transmits a HIGH level, while another master is transmitting a LOW level
will switch off its DATA output state because the level on the bus doesn’t correspond to its own level.
Arbitration continues for many bits until a winning master gets the ownership of I
2
C bus. Its first stage
is comparison of the address bits.
11.9.8 Operation
The I
2
C is byte-oriented and interrupt based. Interrupts are issued after all bus events except for a
transmission of a START condition. Because the I
2
C is interrupt based, the application software is
free to carry on other operations during a I
2
C byte transfer.
Note that when a I
2
C interrupt is generated, IIF flag in I2CMR register is set, it is cleared by writing
an arbitrary value to I2CSR. When I
2
C interrupt occurs, the SCL line is hold LOW until writing any
High Counter
Reset
Fast Device
SCLOUT
Slow Device
SCLOUT
SCL
Wait High
Counting
Start High
Counting
Device1
DataOut
SCL on BUS
Device2
DataOut
SDA on BUS
S
Arbitration Process
not adaped
Device 1 loses
Arbitration
Device1 outputs
High
Figure 11-39 Clock Synchronization during Arbitration Procedure
Figure 11-40 Arbitration Procedure of Two Masters