24LC128-ISLASHST datasheet(17/42 Pages) MICROCHIP

17 / 42 page

DS21930B-page 17

24AAXX/24LCXX/24FCXX

6.2

Page Write

The write control byte, word address byte(s), and the

first data byte are transmitted to the 24XX in much the

same way as in a byte write (see Figure 6-3 and

Figure 6-4). The exception is that instead of generating

a Stop condition, the master transmits up to one page

of bytes(1), which is temporarily stored in the on-chip

page buffer. This data is then written into memory once

the master has transmitted a Stop condition. Upon

receipt of each word, the internal address counter is

incremented by one. If the master should transmit more

than one page of data prior to generating the Stop con-

dition, the address counter will roll over and the previ-

ously received data will be overwritten. As with the byte

write operation, once the Stop condition is received, an

internal write cycle begins. During the write cycle, the

24XX will not acknowledge commands.

Page writes can be any number of bytes within a page

(up to the page size), starting at any address. Only the

data bytes being addressed will be changed within the

page.

If an attempt is made to write to the array with the WP

pin held high, the device will acknowledge the

command, but no write cycle will occur, no data will be

written and the device will immediately accept a new

command.

6.3

Write-Protection

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

when the pin is tied to VCC. See Device Selection

Table 1-1 for the write-protect scheme of each device.

If tied to VSS, the write protection is disabled. The WP

pin is sampled prior to the Stop bit for every Write

command (Figure 2-1). Toggling the WP pin after the

Stop bit will have no effect on the execution of the write

cycle.

FIGURE 6-3:

PAGE WRITE: 1 KB TO 16 KBIT DEVICES

FIGURE 6-4:

PAGE WRITE: 32 TO 512 KBIT DEVICES

* See Table 1-1 for maximum number of data bytes in a page.

Note 1: See Device Selection Table 1-1 for the

page size of each device.

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 (over-

writing data previously stored there),

instead of being written to the next

page, as might be expected. It is there-

fore necessary for the application soft-

ware to prevent page write operations

that would attempt to cross a page

boundary.

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

Address

Byte

Initial

Final

Second

Data Byte

Data Byte*

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

High Order

Address Byte

Low Order

Address Byte

Initial

Final

Data Byte

Data Byte*

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