1.Can I overwrite a page (256 byte) of data instead of going for erase of entire 4kB sector followed by write?
A. No you can overwrite a page with our erasing the sector. Basically overwriting or updating involves erase and then writing.It is because of the nature of flash devices. In flash you can not transition from 0 to 1. It is always 1 to 0. So when you want to overwrite, you need you will make all the locations as 1 and then make them zero where ever it is necessary. Since erase is involved, the lowest section of flash you can erase is sector. It is not possible to erase individual pages.
2.Can you refer me some material that will make it simpler to understand Flash read/write/erase process,especially the ones provided by Cypress?
A) As you are planning to use S25FS256S please refer the FS-S programming guide. Please refer the link below and let us know if you need any clarifications. Hope it helps you.
Hello Krishna, Thank You for your response. Yes it helps for now. Regards, Sonam