256 bytes in the memory space (200000h-20000FFh) are designated as ID locations where the user can store checksum or other code identification numbers. These locations are readable and writable during normal execution. See the “User ID, Device ID and Configuration Word Access ” in the “(NVM) Nonvolatile Memory Control” chapter for more information on accessing these memory locations. For more information on checksum calculation, see the “PIC18F26/45/46Q10 Memory Programming Specification”, (DS40001874).