24LC512-ESLASHP datasheet(9/26 Pages) MICROCHIP

9 / 26 page

DS21754G-page 9

24AA512/24LC512/24FC512

6.0

WRITE OPERATIONS

6.1

Byte Write

Following the Start condition from the master, the

control code (four bits), the Chip Select (three bits) and

the R/W bit (which is a logic low) are clocked onto the

bus by the master transmitter. This indicates to the

addressed slave receiver that the address high byte will

follow after it has generated an Acknowledge bit during

the ninth clock cycle. Therefore, the next byte

transmitted by the master is the high-order byte of the

word address and will be written into the Address

Pointer of the 24XX512. The next byte is the Least

Significant Address Byte. After receiving another

Acknowledge signal from the 24XX512, the master

device will transmit the data word to be written into the

addressed memory location. The 24XX512 acknowl-

edges again and the master generates a Stop

condition. This initiates the internal write cycle and

during this time, the 24XX512 will not generate

Acknowledge signals (Figure 6-1). 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. After a byte

Write command, the internal address counter will point

to the address location following the one that was just

written.

6.2

Page Write

The write control byte, word address and the first data

byte are transmitted to the 24XX512 in the same way

as in a byte write. But instead of generating a Stop

condition, the master transmits up to 127 additional

bytes, which are temporarily stored in the on-chip page

buffer and will be written into memory after the master

has transmitted a Stop condition. After receipt of each

word, the seven lower Address Pointer bits are inter-

nally incremented by one. If the master should transmit

more than 128 bytes 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 will begin (Figure 6-2). 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 entire

array (0000-FFFF) when the pin is tied to VCC. If tied to

VSS the write protection is disabled. The WP pin is

sampled at the Stop bit for every Write command

(Figure 1-1). Toggling the WP pin after the Stop bit will

have no effect on the execution of the write cycle.

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.

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