CAT24C164
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4
Power-On Reset (POR)
CAT24C164 incorporates Power−On Reset (POR)
circuitry which protects the internal logic against powering
up in the wrong state.
A CAT24C164 device will power up into Standby mode
after V
CC
exceeds the POR trigger level and will power
down into Reset mode when V
CC
drops below the POR
trigger level. This bi−directional POR feature protects the
device against ‘brown−out’ failure following a temporary
loss of power.
Pin Description
SCL: The Serial Clock input pin accepts the Serial Clock
generated by the Master.
SDA: The Serial Data I/O pin receives input data and
transmits data stored in EEPROM. In transmit mode, this pin
is open drain. Data is acquired on the positive edge, and is
delivered on the negative edge of SCL.
A
0
, A
1
and A
2
: The Address inputs set the device address
when cascading multiple devices. When not driven, these
pins are pulled LOW internally.
The CAT24C164 can be made compatible with the
CAT24C16 by tying A
2
, A
1
and A
0
to V
SS
or by leaving A
2
,
A
1
and A
0
float.
WP: The Write Protect input pin inhibits all write
operations, when pulled HIGH. When not driven, this pin is
pulled LOW internally.
Functional Description
The CAT24C164 supports the Inter−Integrated Circuit
(I
2
C) 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 CAT24C164 acts as a
Slave device. Master and Slave alternate as either
transmitter or receiver.
I
2
C Bus Protocol
The I
2
C bus consists of two ‘wires’, SCL and SDA. The
two wires are connected to the V
CC
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 SDA line to ‘transmit’ a ‘0’ and
releases it to ‘transmit’ a ‘1’.
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 2). The START condition precedes all commands. It
consists of a HIGH to LOW transition on SDA while SCL
is HIGH. The START acts 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.
Device Addressing
The bus Master begins a transmission by sending a
START condition. The Master then sends the address of the
particular Slave device it is requesting. The most significant
bit of the 8−bit slave address is fixed as 1. (see Figure 3). The
next three significant bits (A
2
, A
1
, A
0
) are the device address
bits and define which device or which part of the device the
Master is accessing (The A
1
bit must be the compliment of
the A
1
input pin signal). Up to eight CAT24C164 devices
may be individually addressed by the system. The next three
bits are used as the three most significant bits of the data
word address. The last bit of the slave address specifies
whether a Read or Write operation is to be performed. When
this bit is set to 1, a Read operation is selected, and when set
to 0, a Write operation is selected.
Acknowledge
After processing the Slave address, the Slave responds
with an acknowledge (ACK) by pulling down the SDA line
during the 9
th
clock cycle (Figure 4). 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 9
th
clock cycle. As
long as the Master acknowledges the data, the Slave will
continue transmitting. The Master terminates the session by
not acknowledging the last data byte (NoACK) and by
issuing a STOP condition. Bus timing is illustrated in
Figure 5.
