I am trying to make PIC16F877 programmer now a days! ,I know this has been successfully done with 89c51 chips .Actually what they DEVILS :twisted: do is they delay the erase pulse using MMVs which applies a shorter pulse and then terminates the programmer. Now what does that means to you ?
Simple when the programmer tries to erase the data it first erases the Fuse bits and then the FLASH ,Now if one could stop it just in the bigining and thats in nano seconds then It could break the FUSES and not the entire data which could be read back .
YOUR PRECAUTIONS TO BE TAKEN
1) FIRST LOCK THE MCU THOROUGHLY.
2) USE SMD VERSION OF MCU AND DIP THE ENTIRE UNIT IN EPOXY :wink:
3) SECRETLY BRING THE PROGRAMMER TERMINALS OUTSIDE ENCRYPT
THEM ,YOU CABN DO THAT AS YOU ARE USING SMD VERSION INSIDE EPOXY .
THIS WILL MAKE VERY HARD FOR THE :twisted: TO BREAK OR EVEN FIND PROGRRAMING LEADS IN THE SYSTM SAY RB6,RB7,RB3 JUST ENCRYPT THEM .
4) IF YOU ARE MAKING SOME VERY SECRET PROJECT USE ANOTHER MCU TO ENCRYPT THE PROGRAMMING PINS OF THE MAIN MCU .
HOPE YOU LIKED MY IDEAS!
Good Luck
Surge