CAT24AA08WI-GT10 Просмотр технического описания (PDF) - ON Semiconductor

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CAT24AA08WI-GT10

4-Kb and 8-Kb I2C CMOS Serial EEPROM

ON Semiconductor 

CAT24AA04, CAT24AA08

Power−On Reset (POR)

Each CAT24AA04/08 incorporates Power−On Reset

(POR) circuitry which protects the internal logic against

powering up in the wrong state. The 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 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 CAT24AA04/08 supports the Inter−Integrated

Circuit (I2C) Bus protocol. The protocol relies on the use of

a Master device, which provides the clock and directs bus

traffic, and Slave devices which execute requests. The

CAT24AA04/08 operates as a Slave device. Both Master

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

assign those roles.

I2C Bus Protocol

The 2−wire I2C bus consists of two lines, SCL and SDA,

connected to the VCC supply via pull−up resistors. The

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). The next three bits from the Slave

address byte are assigned as shown in Figure 3, where a9 and

a8 are internal address bits.The last bit, R/W, instructs the

Slave to either provide (1) or accept (0) data, i.e. it specifies

a Read (1) or a Write (0) operation.

Acknowledge

During the 9th clock cycle following every byte sent onto

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.

SCL

SDA

START

CONDITION

Figure 2. Start/Stop Timing

STOP

CONDITION

1 0 1 0 0 0 a8 R/W CAT24AA04

1 0 1 0 0 a9 a8 R/W CAT24AA08

Figure 3. Slave Address Bits

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