AT45DB021E datasheet(20/69 Pages) RENESAS

20 / 69 page

DS-AT45DB021E-8789 Rev. N

Page 20

3/24/26

AT45DB021E Datasheet

To perform a Read-Modify-Write using the binary page size (256 bytes), an opcode of 58h for Buffer 1 must be

clocked into the device followed by three address bytes comprised of six dummy bits, 10 page address bits (A17 -

A8) that specify the page in the main memory to be written and eight byte address bits (A7-A0) that designate the

starting byte address within the page to reprogram.

After the address bytes have been clocked in, any number of sequential data bytes from one to 256/264 bytes can

be clocked into the device. If the end of the buffer is reached when clocking in the data, then the device wraps

around back to the beginning of the buffer. After all data bytes have been clocked into the device, a low-to-high

transition on the CS pin starts the self-contained, internal read-modify-write operation. Only the data bytes that

were clocked into the device are reprogrammed in the main memory.

Example: If only one data byte was clocked into the device, then only one byte in main memory is reprogrammed

and the remaining bytes in the main memory page remain in their previous state.

The CS pin must be deasserted on a byte boundary (multiples of eight bits); otherwise, the operation is aborted

and no data is programmed. The reprogramming of the data bytes is internally self-timed and must take place in a

maximum time of tP. During this time, the RDY/BUSY bit in the Status Register indicates that the device is busy.

The device also incorporates an intelligent erase and programming algorithm that can detect when a byte location

fails to erase or program properly. If an erase or program error arises, it is indicated by the EPE bit in the Status

Note: The Read-Modify-Write command uses the same opcodes as the Auto Page Rewrite command. If no data

bytes are clocked into the device, then the device performs an Auto Page Rewrite operation. See “Auto Page

Rewrite” on page 30 for more details.

AT45DB021E Datasheet(PDF) 20 Page - Renesas Technology Corp