I am trying to understand the PDF From the following URL: Spansion Application Note
Under the heading Flash Address Pin Labels, it describes that "In word mode there is no means to individually select a byte within a word".
Can someone explain why this behavior?
In Table-1 & Table-2 of the same document in one case A(-1) is shown as 0 and 1 respectively. Is there any correspondence between them or it fixed?
Thanks for your time.
Best Regards,
GSR
Best Answer
In word mode, you can only access the flash in a word-aligned way, so the lowest address bit, representing a byte, is not available. This is a quite common restriction in microcontrollers as well. Trying to access not in word aligned mode might give unpredictable behavior - so they prevent it.
In byte more, the least significant bit becomes available so A(-1) can be used to address also a single byte at any place. The read logic will be more complex to do that if the memory is normally accessed in word-mode.
The Table-1 and Table-2 show how to unlock the flash for advanced commands. The way to do it depends on the mode selected, so byte mode and word mode use different patterns to get to the advanced commands displayed in Table-3.