24FC08-ESLASHST datasheet(9/49 Pages) MICROCHIP

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DS20001710N-page 9

24AA08/24LC08B/24FC08

5.0

DEVICE ADDRESSING

A control byte is the first byte received following the

Start condition from the host device. The control byte

consists of a four-bit control code. For the 24XX08, this

is set as ‘

1010’ binary for read and write operations.

The next bit of the control byte is a “don’t care” for the

24XX08. The last two bits, B1 and B0, are used by the

host device to select which of the four 256-word blocks

of memory are to be accessed. These bits, in effect, are

the Most Significant bits of the word address. The

combination of the 4-bit control code and the next three

bits are called the client address.

The last bit of the control byte is the Read/Write (R/W)

bit and it defines the operation to be performed. When

set to ‘

1’, a read operation is selected. When set to ‘0’,

a write operation is selected. Following the Start

condition, the 24XX08 monitors the SDA bus, checking

the device type identifier being transmitted. Upon

receiving a valid client address and the R/W bit, the

client device outputs an Acknowledge signal on the

SDA line. Depending on the state of the R/W bit, the

24XX08 will select a read or write operation.

The next byte received defines the address of the first

data byte within the selected block (Figure 5-2). The

word address byte uses all eight bits.

FIGURE 5-1:

CONTROL BYTE

ALLOCATION

FIGURE 5-2:

ADDRESS SEQUENCE BIT ASSIGNMENTS

Operation

Control

Code

Block Select

R/W

Read

1010

Block Address

Write

1010

Block Address

B1 B0 R/W ACK

Start Bit

Read/Write Bit

x = “don’t care”

Client Address

Acknowledge Bit

Control Code

Block

Select

Bits

010

x B1

R/W

••

•

Control Byte

Word Address Byte

Control

Code

Block

Select

Bits

x = “don’t care”

•

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