Flash memory operation 1 - data writing -

The initial state of Flash memory is a state in which all bits are 1.

​The only write operation in Flash memory is to change 1 data to 0.

You cannot go from 0 to 1, which is the inverse operation. Also, although the unit that can be written differs depending on the device, it is generally 1 Byte unit or word (2 Byte) unit.

However, with this method, data once written cannot be changed. What should I do?

Flash memory operation 2 - data erasure -

Another operation that Flash memory can do is erasing data.

However, this erase operation will change all 0 data to 1 block by block.

Block sizes vary by device, but can be quite large for writes, such as 64 KB.

There are only two ways to change data in Flash memory.

So overwriting it takes a little effort.

As an example, let's use the PC as the host and change the yellow colored part of the data in the Flash memory.

You save it in a buffer once, modify that data, and write it to Flash memory.

Also, if the process of writing all 0s to the flash memory is automatically performed by the flash memory, there is no need to be aware of it.

As you can see, even changing just one bit in Flash requires many steps.