24AA04/24LC04B

DS21708G-page 6

© 2007 Microchip Technology Inc.

3.6

Device Addressing

A control byte is the first byte received following the

Start condition from the master device. The control byte

consists of a four-bit control code. For the 24XX04, this

The next two bits of the control byte are “don’t cares” for

the 24XX04. The last bit, B0, is used by the master

device to select which of the two 256-word blocks of

memory are to be accessed. This bit is, in effect, the

Most Significant bit of the word address.

The last bit of the control byte defines the operation to

Following the Start condition, the 24XX04 monitors the

SDA bus checking the device type identifier being

slave device outputs an Acknowledge signal on the

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

24XX04 will select a read or write operation.

FIGURE 3-2:

CONTROL BYTE

ALLOCATION

Operation

Control

Code

Block Select

R/W

Read

1010

Block Address

1

Write

1010

Block Address

0

10

1

0

xx

B0 R/W ACK

Start Bit

Read/Write Bit

x = “don’t care”

S

Slave Address

Acknowledge Bit

Control Code

Block

Select

Bits