NOR Flash Interfacing
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.