X24C02

5

DEVICE ADDRESSING

Following a start condition the master must output the

address of the slave it is accessing. The most significant

four bits of the slave are the device type identifier

(see Figure 4). For the X24C02 this is fixed as 1010[B].

The next three significant bits address a particular device.

A system could have up to eight X24C02 devices

on the

bus (see Figure 10). The eight addresses are defined by the

The last bit of the slave address defines the operation to be

performed. When set to one a read operation is

selected, when set to zero a write operations is selected.

Figure 4. Slave Address

Following the start condition, the X24C02 monitors the

SDA bus comparing the slave address being transmitted

acknowledge on the SDA line. Depending on the state of the

R/W bit, the X24C02 will execute a read or write

operation.

WRITE OPERATIONS

Byte Write

For a write operation, the X24C02 requires a second

address field. This address field is the word address,

comprised of eight bits, providing access to any one of the

256 words of memory. Upon receipt of the word

address the X24C02 responds with an acknowledge, and

awaits the next eight bits of data, again responding

with an acknowledge. The master then terminates the

transfer by generating a stop condition, at which time the

X24C02 begins the internal write cycle to the nonvolatile

memory. While the internal write cycle is in progress the

X24C02 inputs are disabled, and the device will not

respond to any requests from the master. Refer to

Figure 5 for the address, acknowledge and data transfer

sequence.

1

0

1

0

A2

A1

A0

R/W

DEVICE TYPE

IDENTIFIER

DEVICE

ADDRESS

Figure 6. Page Write

Figure 5. Byte Write

BUS ACTIVITY:

MASTER

SDA LINE

BUS ACTIVITY:

X24C02

S

T

A

R

T

SLAVE

ADDRESS

S

S

T

O

P

P

A

C

K

A

C

K

A

C

K

WORD

ADDRESS

DATA

3838 FHD F010

3838 FHD F011

3838 FHD F09

BUS ACTIVITY:

MASTER

SDA LINE

BUS ACTIVITY:

X24C02

S

T

A

R

T

SLAVE

ADDRESS

S

S

T

O

P

P

A

C

K

A

C

K

A

C

K

A

C

K

A

C

K

WORD

ADDRESS (n)

DATA n

DATA n+1

DATA n+3

NOTE: In this example n = xxxx 000 (B); x = 1 or 0