CAT24C01/02/04/08/16
I2C BUS PROTOCOL
POWER-ON RESET (POR)
The I2C bus consists of two ‘wires’, SCL and SDA. The
two wires are connected to the VCC supply via pull-up
resistors. Master and Slave devices connect to the 2-
wire bus via their respective SCL and SDA pins. The
transmitting device pulls down the SDAline to ‘transmit’
a ‘0’ and releases it to ‘transmit’ a ‘1’.
Each CAT24Cxx* incorporates Power-On Reset (POR)
circuitry which protects the internal logic against
powering up in the wrong state.
A CAT24Cxx device will power up into Standby mode
after VCC exceeds the POR trigger level and will power
down into Reset mode when VCC drops below the POR
trigger level. This bi-directional POR feature protects
the device against ‘brown-out’ failure following a
temporary loss of power.
Data transfer may be initiated only when the bus is not
busy (see A.C. Characteristics).
During data transfer, the SDA line must remain stable
while the SCL line is HIGH. An SDA transition while
SCL is HIGH will be interpreted as a START or STOP
condition (Figure 1). The START condition precedes all
commands. It consists of a HIGH to LOW transition on
SDAwhile SCLis HIGH. The STARTacts as a ‘wake-up’
call to all receivers. Absent a START, a Slave will not
respond to commands. The STOP condition completes
all commands. It consists of a LOW to HIGH transition
on SDA while SCL is HIGH.
* For common features, the CAT24C01/02/04/08/16 will be refered
to as CAT24Cxx
PIN DESCRIPTION
SCL:The Serial Clock input pin accepts the Serial Clock
generated by the Master.
Device Addressing
SDA: The Serial Data I/O pin receives input data and
transmitsdatastoredinEEPROM.Intransmitmode,this
pin is open drain. Data is acquired on the positive edge,
and is delivered on the negative edge of SCL.
The Master initiates data transfer by creating a START
condition on the bus. The Master then broadcasts an
8-bitserialSlaveaddress.FornormalRead/Writeopera-
tions, the first 4 bits of the Slave address are fixed at
1010 (Ah). The next 3 bits are used as programmable
address bits when cascading multiple devices and/or as
internal address bits. The last bit of the slave address,
R/W, specifies whether a Read (1) or Write (0) operation
is to be performed. The 3 address space extension bits
are assigned as illustrated in Figure 2. A2, A1 and A0
must match the state of the external address pins, and
a10, a9 and a8 are internal address bits.
A0, A1 and A2: The Address inputs set the device ad-
dresswhencascadingmultipledevices.Whennotdriven,
these pins are pulled LOW internally.
WP: The Write Protect input pin inhibits all write opera-
tions, when pulled HIGH. When not driven, this pin is
pulled LOW internally.
Acknowledge
After processing the Slave address, the Slave responds
with an acknowledge (ACK) by pulling down the SDA
line during the 9th clock cycle (Figure 3). The Slave will
also acknowledge the address byte and every data byte
presented in Write mode. In Read mode the Slave shifts
out a data byte, and then releases the SDA line during
the 9th clock cycle.As long as the Master acknowledges
thedata, theSlavewillcontinuetransmitting.TheMaster
terminates the session by not acknowledging the last
data byte (NoACK) and by issuing a STOP condition.
Bus timing is illustrated in Figure 4.
FUNCTIONAL DESCRIPTION
TheCAT24CxxsupportstheInter-IntegratedCircuit(I2C)
Bus data transmission protocol, which defines a device
that sends data to the bus as a transmitter and a device
receiving data as a receiver. Data flow is controlled by
a Master device, which generates the serial clock and
all START and STOP conditions. The CAT24Cxx acts
as a Slave device. Master and Slave alternate as either
transmitter or receiver.
© 2006 by Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
Doc. No. 1115, Rev. C
4
CATALYST [ CATALYST SEMICONDUCTOR ]
