X24164

5

DEVICE ADDRESSING

Following a start condition the master must output the

address of the slave it is accessing. The most significant

bit of the slave is a one (see Figure 4). The next three bits

are the device select bits. A system could have up to

eight X24164’s on the bus. The eight addresses are

slave address must be the inverse of 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 operation is selected.

Following the start condition, the X24164 monitors the

SDA bus comparing the slave address being transmit-

ted with its slave address device type identifier. Upon a

correct compare the X24164 outputs an acknowledge

on the SDA line. Depending on the state of the R/

W bit,

the X24164 will execute a read or write operation.

WRITE OPERATIONS

Byte Write

For a write operation, the X24164 requires a second

address field. This address field is the word address,

comprised of eight bits, providing access to any one of

2048 words in the array. Upon receipt of the word

address the X24164 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

X24164 begins the internal write cycle to the nonvolatile

memory. While the internal write cycle is in progress the

X24164 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 4. Slave Address

The next three bits of the slave address are an extension

of the array’s address and are concatenated with the

eight bits of address in the word address field, providing

direct access to the whole 2048 x 8 array.

Figure 5. Byte Write

3846 FHD F10

3846 FHD F11

BUS ACTIVITY:

MASTER

SDA LINE

BUS ACTIVITY:

X24164

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

1

S2

A2

A1

A0

R/W

DEVICE

SELECT

S1

S0

HIGH

ORDER

WORD

ADDRESS