At 02:10 PM 6/10/2004, Sean A. Walberg wrote: >I've got a 16F876 on a breadboard connected to a MAX232, and am >programming it with an Olimex PG2C (JDM) programmer using ICSP. > >With the MAX all wired up, programming fails after the first few words >(the software I use programs a word, verifys, then does the next word). >If I disconnect the Vss pin, it works fine. > >Are there any guidelines for building a circuit with ICSP in mind? I've >found information about using RB6/7 (ie LEDs are bad), but this ground >thing has me stumped. I thought it might be the serial port ground from >the MAX, but disconnecting that didn't help. Peter Anderson has a good description of why ICSP is not a good idea with the JDM programmer but, in a nutshell, the JDM is likely to fail if any of the serial pins on the target connect to any external ground. Your situation may be slightly different - it sounds as if you may be using some of the handshake lines in your circuit. If that is the case, remove the MAX232 and try it again. Then have a close look at how the JDM programmer derives Vpp and see how that is affected by the handshake lines being connected to the MAX232. If you follow the sneak current paths that occur as a result of the unconventional way the JDM gets Vpp, you should see why it fails. Summary: the JDM programmer connects your circuit common to one of its handshake lines and drives it to the negative rail. Vdd comes from the programming computer's ground line (this is reasonable since Vss is below ground) and Vpp comes from one of the other handshake lines driven to the positive rail. Hope this helps. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 20 years of Engineering Innovation (1984 - 2004) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics