24LC02B datasheet(7/24 Pages) MICROCHIP

7 / 24 page

 2003 Microchip Technology Inc.

DS21709C-page 7

24AA02/24LC02B

4.0

WRITE OPERATION

4.1

Byte Write

Following the Start condition from the master, the

device code (4 bits), the block address (3 bits, ‘don’t

cares’) 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 Acknowl-

edge bit during the ninth clock cycle. Therefore, the

next byte transmitted by the master is the word address

and will be written into the address pointer of the

24XX02. After receiving another Acknowledge signal

from the 24XX02, the master device will transmit the

data word to be written into the addressed memory

location. The 24XX02 acknowledges again and the

master generates a Stop condition. This initiates the

internal write cycle and, during this time, the 24XX02

will not generate Acknowledge signals (Figure 4-1).

4.2

Page Write

The write-control byte, word address and the first data

byte are transmitted to the 24XX02 in the same way as

in a byte write. However, instead of generating a Stop

condition, the master transmits up to 8 data bytes to the

24XX02, 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 8 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 4-2).

FIGURE 4-1:

BYTE WRITE

FIGURE 4-2:

PAGE 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

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

WORD

ADDRESS (n)

DATA (n)

DATA (n + 7)

DATA (n + 1)

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