24AA04_09 datasheet(8/34 Pages) MICROCHIP

8 / 34 page

24AA04/24LC04B

DS21708K-page 8

6.0

WRITE OPERATION

6.1

Byte Write

Following the Start condition from the master, the

device code (4 bits), the block address (3 bits) and the

R/W bit, which is a logic-low, is placed onto the bus by

the master transmitter. This indicates to the addressed

slave receiver that a byte with a word address will

follow once it has generated an Acknowledge bit during

the ninth clock cycle. Therefore, the next byte transmit-

ted by the master is the word address and will be

written into the Address Pointer of the 24XX04. After

receiving

another

Acknowledge

signal

from

the

24XX04, the master device will transmit the data word

to be written into the addressed memory location. The

24XX04

acknowledges

again

and

the

master

generates a Stop condition. This initiates the internal

write cycle and, during this time, the 24XX04 will not

generate Acknowledge signals (Figure 6-1).

6.2

Page Write

The write control byte, word address and the first data

byte are transmitted to the 24XX04 in the same way as

in a byte write. But instead of generating a Stop condi-

tion the master transmits up to 16 data bytes to the

24XX04, which are temporarily stored in the on-chip

page buffer and will be written into memory once the

master has transmitted a Stop condition. Upon receipt

of each word, the four lower-order Address Pointer bits

are internally incremented by ‘1’. The higher-order 7

bits of the word address remain constant. If the master

should transmit more than 16 words prior to generating

the Stop condition, the address counter will roll over

and the previously received data will be overwritten. As

with the byte write operation, once the Stop condition is

received an internal write cycle will begin (Figure 6-2).

6.3

Write Protection

The WP pin allows the user to write-protect the entire

array (000-1FF) when the pin is tied to VCC. If tied to

VSS the write protection is disabled.

The Chip Scale package does not suport the write-

protect feature.

FIGURE 6-1:

BYTE WRITE

Note:

Page write operations are limited to writing

bytes within a single physical page

regardless of the number of bytes

actually being written. Physical page

boundaries start at addresses that are

integer multiples of the page buffer size (or

‘page size’) and end at addresses that are

integer multiples of [page size – 1]. If a

page write command attempts to write

across a physical page boundary, the

result is that the data wraps around to the

beginning of the current page (overwriting

data previously stored there), instead of

being written to the next page as might be

expected. It is therefore necessary for the

application software to prevent page write

operations that would attempt to cross a

page boundary.

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

Word

Address

Data

Block

Select

Bits

= “don’t care”

x B0 0

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