34LC02-ISLASHP datasheet(9/40 Pages) MICROCHIP

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DS20002029G-page 9

34AA02/34LC02

5.0

DEVICE ADDRESSING

A control byte is the first byte received following the

Start condition from the host device. The first part of the

control byte consists of a 4-bit control code which is set

to ‘1010’ for normal read and write operations

and ‘0110’ for writing to the write-protect register. The

control byte is followed by three Chip Select bits (A2,

A1, A0). The Chip Select bits allow the use of up to

eight 34XX02 devices on the same bus and are used to

determine which device is accessed. The Chip Select

bits in the control byte must correspond to the logic

levels on the corresponding A2, A1 and A0 pins for the

device to respond. These bits are in effect the three

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.

For the SOT-23 package, the A2 pin is not connected.

During device addressing, the A2 Chip Select bit

should be set to ‘0’. Only four 34XX02 SOT-23 pack-

ages can be connected to the same bus.

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

a'0', a write operation is selected. Following the Start

condition, the 34XX02 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

34XX02 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 FORMAT

FIGURE 5-2:

ADDRESS SEQUENCE BIT ASSIGNMENTS

Operation

Control

Code

Chip

Select

R/W

Read

1010

A2 A1 A0

Write

1010

A2 A1 A0

Write-Protect Register

0110

A2 A1 A0

Start

Read/Write

Client Address

R/W A

010

R/W

••

•

Control Byte

Word Address Byte

Control

Code

Chip

Select

bits

x = “don’t care”

•

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