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AT24C256C

8568A–SEEPR–11/08

5.

Write Operations

BYTE WRITE: A write operation requires two 8-bit data word addresses following the device address word and

acknowledgment. Upon receipt of this address, the EEPROM will again respond with a “0” and then clock in the first

8-bit data word. Following receipt of the 8-bit data word, the EEPROM will output a “0”. The addressing device, such as

a microcontroller, must then terminate the write sequence with a stop condition. At this time the EEPROM enters an

internally-timed write cycle, t

to the nonvolatile memory. All inputs are disabled during this write cycle and the

EEPROM will not respond until the write is complete (refer to Figure 9).

Figure 9.

Byte Write

Note:

* = DON’T CARE bit

PAGE WRITE: The 256K EEPROM is capable of 64-byte page writes.

A page write is initiated the same way as a byte write, but the microcontroller does not send a stop condition after the

first data word is clocked in. Instead, after the EEPROM acknowledges receipt of the first data word, the microcontroller

can transmit up to 63 more data words. The EEPROM will respond with a “0” after each data word received. The

microcontroller must terminate the page write sequence with a stop condition (refer to Figure 10).

Figure 10.

Page Write

Note:

* = DON’T CARE bit

The data word address lower six bits are internally incremented following the receipt of each data word. The higher

data word address bits are not incremented, retaining the memory page row location. When the word address,

internally generated, reaches the page boundary, the following byte is placed at the beginning of the same page. If

more than 64 data words are transmitted to the EEPROM, the data word address will “roll over” and previous data will

be overwritten. The address “roll over” during write is from the last byte of the current page to the first byte of the same

page.

ACKNOWLEDGE POLLING: Once the internally-timed write cycle has started and the EEPROM inputs are disabled,

acknowledge polling can be initiated. This involves sending a start condition followed by the device address word. The

read/write bit is representative of the operation desired. Only if the internal write cycle has completed will the EEPROM

respond with a “0”, allowing the read or write sequence to continue.