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System Memory Controller (SMC)
3
The ASIC has an I2C (Inter-Integrated Circuit) two-wire serial interface
bus: Serial Clock Line (SCL) and Serial Dat a L ine (SDA). This interface
has master-only capability and may be used to communicate the
configuration information to a slave I2C device such as serial EEPROM.
The I2C interface is compatible with these devices , and the inclusion of a
serial EEPROM in the memory subsystem may be desirable. The
EEPROM could maintain the configuration in formation related to the
memory subsystem even when the power is removed from the system.
Each slave device connected to the I2C bus is software addressable by a
unique address. The number of interfaces connected to the I2C bus is solely
dependent on the bus capacitance limit of 400pF.
For I2C bus programming, the ASIC is the only master on the bus and the
serial EEPROM devices are all slaves . The I2C bus supports 7-bit
addressing mode and transmits data one byte at a time in a serial fashion
with the most significant bit (MSB) being sent out first. Five registers are
required to perform the I2C bus data transfer operations. These are the I2C
Clock Prescaler Register, I2C Control Register, I2C Status Register, I2C
Transmitter Data Register, and I2C Receiver Data Register.
The I2C SDA is an open-drain bi-directional line on which data can be
transferred at a rate up to 100 Kbits/s in the standard mode, or up to 400
kbits/s in the fast mode. The I2C serial clock (SCL) is programmable via
I2_PRESCALE_VAL bits in the I2C Clock Prescaler Register. The I2C
clock frequency is determined by the following formula:
I2C CLOCK = SYSTEM CLOCK / (I2_PRESCALE_VAL+1) / 2
The I2C bus has the ability to perform byte write, page write, current
address read, random read, and sequential read operations.