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IIC-BUS INTERFACE S3C2440A RISC MICROPROCESSOR
20-6
READ-WRITE OPERATION
In Transmitter mode, when the data is transferred, the IIC-bus interface will wait until IIC-bus Data Shift (IICDS)
register receives a new data. Before the new data is written into the register, the SCL line will be held low, and then
released after it is written. The S3C2440A should hold the interrupt to identify the completion of current data
transfer. After the CPU receives the interrupt request, it should write a new data into the IICDS register, again.
In Receive mode, when data is received, the IIC-bus interface will wait until IICDS register is read. Before the new
data is read out, the SCL line will be held low and then released after it is read. The S3C2440A should hold the
interrupt to identify the completion of the new data reception. After the CPU receives the interrupt request, it should
read the data from the IICDS register.
BUS ARBITRATION PROCEDURES
Arbitration takes place on the SDA line to prevent the contention on the bus between two masters. If a master with a
SDA High level detects the other master with a SDA active Low level, it will not initiate a data transfer because the
current level on the bus does not correspond to its own. The arbitration procedure will be extended until the SDA line
turns High.
However, when the masters simultaneously lower the SDA line, each master should evaluate whether the
mastership is allocated itself or not. For the purpose of evaluation is that each master should detect the address
bits. While each master generates the slaver address, it should also detect the address bit on the SDA line because
the SDA line is likely to get Low rather than to keep High. Assume that one master generates a Low as first address
bit, while the other master is maintaining High. In this case, both masters will detect Low on the bus because the
Low status is superior to the High status in power. When this happens, Low (as the first bit of address) generating
master will get the mastership while High (as the first bit of address) generating master should withdraw the
mastership. If both masters generate Low as the first bit of address, there should be arbitration for the second
address bit, again. This arbitration will continue to the end of last address bit.
ABORT CONDITIONS
If a slave receiver cannot acknowledge the confirmation of the slave address, it should hold the level of the SDA line
High. In this case, the master should generate a Stop condition and to abort the transfer.
If a master receiver is involved in the aborted transfer, it should signal the end of the slave transmit operation by
canceling the generation of an ACK after the last data byte received from the slave. The slave transmitter should
then release the SDA to allow a master to generate a Stop condition.
CONFIGURING IIC-BUS
To control the frequency of the serial clock (SCL), the 4-bit prescaler value can be programmed in the IICCON
register. The IIC-bus interface address is stored in the IIC-bus address (IICADD) register. (By default, the IIC-bus
interface address has an unknown value.)