X24026

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 X24026 this is fixed as 1010[B].

Figure 4. Slave Address

The next three significant bits are reserved address bits.

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.

Following the start condition, the X24026 monitors the

SDA bus comparing the slave address being transmitted

with its slave address. Upon a correct compare the

X24026 outputs an acknowledge on the SDA line.

Depending on the state of the R/W bit, the X24026 will

execute a read or write operation.

WRITE OPERATIONS

Byte Write

For a write operation, the X24026 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 X24026 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 X24026

begins the internal write cycle to the nonvolatile memory.

While the internal write cycle is in progress the X24026

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.

Figure 5. Byte Write

Figure 6. Page Write

1

7020 FRM 06

0

1

0

0

0

0

R/W

DEVICE TYPE

IDENTIFIER

RESERVE

ADDRESS

BITS

BUS ACTIVITY:

MASTER

SDA LINE

X24026

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

7020 FRM 07

BUS ACTIVITY:

BUS ACTIVITY:

MASTER

SDA LINE

X24026

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

7020 FRM 08

BUS ACTIVITY: