AT45DB021E datasheet(20/74 Pages) DIALOG

20 / 74 page

AT45DB021E

DS-AT45DB021E—8789J—03/2021

7.10 Read-Modify-Write

A completely self-contained read-modify-write operation can be performed to reprogram any number of sequential

bytes in a page in the main memory array without affecting the rest of the bytes in the same page. This command

allows the device to easily emulate an EEPROM by providing a method to modify a single byte or more in the main

memory in a single operation, without the need for pre-erasing the memory or the need for any external RAM

buffers. The Read-Modify-Write command is essentially a combination of the Main Memory Page to Buffer

Transfer, Buffer Write, and Buffer to Main Memory Page Program with Built-in Erase commands.

To perform a Read-Modify-Write using the standard DataFlash page size (264 bytes), an opcode of 58h for Buffer

1 must be clocked into the device followed by three address bytes comprised of five dummy bits, 10 page address

bits (PA9 - PA0) that specify the page in the main memory to be written and nine byte address bits (BA8-BA0) that

designate the starting byte address within the page to reprogram.

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 are programmed. The reprogramming of the data bytes is internally self-timed and takes 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 the Auto Page

Rewrite command description on

page 30 for more details.

AT45DB021E Datasheet(PDF) 20 Page - Dialog Semiconductor