Hi i am using SST25VF032B flash memory. Before writing ,it has to be erased to 0xFF. But my doubt is that how it stores real 0xFF. Will is store 0xFF or some other value?
I'm not sure what you mean.
When you store
0xFF, it stores
0xFF - that is, it sets all 8 bits of the register. The exact same thing happens when you erase the chip. Look at erasing as bulk writing
0xFF to all registers.
In both cases, a read operation would return