In 8085 system where EPROM contans main programe, any one can copy EPROM and copy project so i want to know how to protect our project from copying. Some body told me to use PLD like GAL16V8 for this purpose. How to do this.

The only thing taht you can do is exchange the datas of data bus and address for confusing the copier.
The GAL gets you a particular decoding for each circuit, the program can be readed.