24LC024 datasheet(8/30 Pages) MICROCHIP

8 / 30 page

24AA024/24LC024/24AA025/24LC025

DS21210L-page 8

6.0

WRITE OPERATIONS

6.1

Byte Write

Following the Start signal from the master, the device

code(4 bits), the Chip Select bits (3 bits) and the R/W

bit (which is a logic-low) is placed onto the bus by the

master transmitter. The device will acknowledge this

control byte during the ninth clock pulse. The next byte

transmitted by the master is the word address and will

be written into the Address Pointer of the 24AA024/

24LC024/24AA025/24LC025. After receiving another

Acknowledge signal from the 24AA024/24LC024/

24AA025/24LC025, the master device will transmit the

data word to be written into the addressed memory

location. The 24AA024/24LC024/24AA025/24LC025

acknowledges again and the master generates a Stop

condition. This initiates the internal write cycle and, dur-

ing

this

time,

the

24AA024/24LC024/24AA025/

24LC025 will not generate Acknowledge signals

(Figure 6-1). If an attempt is made to write to the

protected portion of the array when the hardware write

protection (24XX024 only) has been enabled, the

device will acknowledge the command, but no data will

be written. The write cycle time must be observed even

if write protection is enabled.

6.2

Page Write

The write control byte, word address and the first data

byte

are

transmitted

the

24AA024/24LC024/

24AA025/24LC025 in the same way as in a byte write.

However, instead of generating a Stop condition, the

master transmits up to 15 additional data bytes to the

24AA024/24LC024/24AA025/24LC025,

which

are

temporarily stored in the on-chip page buffer and will be

written into the memory once the master has transmit-

ted a Stop condition. Upon receipt of each word, the

four lower-order Address Pointer bits are internally

incremented by one.

The higher-order four bits of the word address remain

constant. If the master should transmit more than 16

bytes 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). If an attempt

is made to write to the protected portion of the array

when the hardware write protection has been enabled,

the device will acknowledge the command, but no data

will be written. The write cycle time must be observed

even if write protection is enabled.

6.3

Write Protection

The WP pin (available on 24XX024 only) must be tied

to VCC or VSS. If tied to VCC, the entire array will be

write-protected. If the WP pin is tied to VSS, write

operations to all address locations are allowed.

FIGURE 6-1:

BYTE WRITE

FIGURE 6-2:

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 + 15)

Data (n +1)

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