Hi all , here is my problem: I have a software running perfectly in a 12C509 OTP Microchip PIC , this PIC has been programmed by myself with the Microchip assembler , and perfectly burned into the OTP device , program is working : no pb . I want modify it , but to avoid using OTP in case of programing errors I programmed a 12C509 Eprom , first of all , without any modifications , that's to say exactly the same content as the running one in OTP. But this one is not running at all... Is there a difference ( or several differences) between a 509 OTP and a 509 Eprom? 73's Dom -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu