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5194F–SEEPR–1/08

AT24C1024B

DATA SECURITY: The AT24C1024B has a hardware data protection scheme that allows the

6. Write Operations

BYTE WRITE: To select a data word in the 1024K memory requires a 17-bit word address. The

address followed by the least significant word address (see Figure 7-2 on page 11)

address word and acknowledgment. Upon receipt of this address, the EEPROM will again

respond with a zero and then clock in the first 8-bit data word. Following receipt of the 8-bit data

word, the EEPROM will output a zero. The addressing device, such as a microcontroller, then

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

write cycle and the EEPROM will not respond until the write is complete (see Figure 7-2 on page

11).

PAGE WRITE: The 1024K EEPROM is capable of 256-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 255 more data words. The

EEPROM will respond with a zero after each data word received. The microcontroller must ter-

minate the page write sequence with a stop condition (see Figure 7-3 on page 11).

The data word address lower 8 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 follow-

ing byte is placed at the beginning of the same page. If more than 256 data words are

transmitted to the EEPROM, the data word address will “roll over” and previous data will be

overwritten. The address “rollover” 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 zero, allowing the read or write sequence to continue.

7. Read Operations

Read operations are initiated the same way as write operations with the exception that the

read/write select bit in the device address word is set to one. There are three read operations:

current address read, random address read and sequential read.

CURRENT ADDRESS READ: The internal data word address counter maintains the last

address accessed during the last read or write operation, incremented by one. This address

stays valid between operations as long as the chip power is maintained. The address “rollover”

during read is from the last byte of the last memory page, to the first byte of the first page.