CAT24AA01, CAT24AA02

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4

Power−On Reset (POR)

Each CAT24AA01/02 incorporates Power−On Reset

(POR) circuitry which protects the internal logic against

powering up in the wrong state. The device will power up

below the POR trigger level.

This bi−directional POR behavior protects the device

against brown−out failure, following a temporary loss of

power.

Pin Description

SCL: The Serial Clock input pin accepts the clock signal

generated by the Master.

SDA: The Serial Data I/O pin accepts input data and delivers

output data. In transmit mode, this pin is open drain. Data is

acquired on the positive edge, and delivered on the negative

edge of SCL.

WP: When the Write Protect input pin is forced HIGH by an

external source, all write operations are inhibited. When the

pin is not driven by an external source, it is pulled LOW

internally.

Functional Description

The CAT24AA01/02 supports the Inter−Integrated

a Master device, which provides the clock and directs bus

traffic, and Slave devices which execute requests. The

CAT24AA01/02 operates as a Slave device. Both Master

and Slave can transmit or receive, but only the Master can

assign those roles.

Master provides the clock to the SCL line, and the Master

and Slaves drive the SDA line. A ‘0’ is transmitted by

pulling a line LOW and a ‘1’ by releasing it HIGH. Data

transfer may be initiated only when the bus is not busy (see

A.C. Characteristics). During data transfer, SDA must

remain stable while SCL is HIGH.

START/STOP Condition

An SDA transition while SCL is HIGH creates a START

or STOP condition (Figure 2). A START is generated by a

HIGH to LOW transition, while a STOP is generated by a

LOW to HIGH transition. The START acts like a wake−up

call. Absent a START, no Slave will respond to the Master.

The STOP completes all commands.

Device Addressing

The Master addresses a Slave by creating a START

condition and then broadcasting an 8−bit Slave address

(Figure 3). The four most significant bits of the Slave

address are 1010 (Ah).

For the CAT24AA01/02 the next three bits must be 000.

The last bit, R/W, instructs the Slave to either provide (1)

or accept (0) data, i.e. it signals a Read (1) or a Write (0)

request.

Acknowledge

the bus, the transmitter releases the SDA line, allowing the

receiver to respond. The receiver then either acknowledges

(ACK) by pulling SDA LOW, or does not acknowledge

(NoACK) by letting SDA stay HIGH (Figure 4). Bus timing

is illustrated in Figure 5.

Figure 2. Start/Stop Timing

START

CONDITION

STOP

CONDITION

SDA

SCL

Figure 3. Slave Address Bits

101000

0

R/W