In 37.3.10 FCR : Flash Control Register, the CMDs for erasing the sector/block states: “Set the start address of the target erasure block in the FSARH and FSARL registers, and set the end address of the target erasure block in the FEARH and FEARL registers.” The “end address of the target erasure block” means 1) “address of the last block to erase”: end_address = block_number  * 0x800 // means start address of block_127 == 0x3F800 2) “last address of the last erasure block”: end_address = (block_number+1) * 0x800 – 1 // means end/last address of block_127 == 0x3FFFF.