Programmable flash memory is located in layer Code from 8000h to FFFFh.
By writing the protection code of "01H" to  address 8001H of the flash 
memory access to the flash memory is risricted. Any other data leave chip 
unprotected. Once the flash memory is protected, performing the chip erase 
operation only can unlock the function. Otherwise read/write access to 
the flash memory from the external pins is not possible.
For more information see device hardware manual.