Hello Shimoeda San,
If the customer wants to protect some of the sectors from program or erase operations where once the data is programmed it does not require to be updated/modified then we provide the option through Highest sector protection or Lowest address sector protection.
For ex : Important programs like boot codes will not change through out the life time of application. IN this case customer can choose to program the code in to either highest or lowest and can get it protected. Please note that once it is locked it can not be changed.
User can choose which sector to be protected Highest or lowest depending on their choice and order part umber accordingly.
Hope it clarifies your query.
Thank you for your support .