On Wed, Sep 22, 2010 at 12:17 PM, Wouter van Ooijen wrote: >> Now, reading all 1s suggests a stuck pin or other short, but these >> other units apear to be sending the ID back shifted one bit to the >> left. Has anyone seen that before?. > > That reeks of clock problems. A small series resistor (47 ohm?) and/or a > small capacitor at the target chip (22pf?) might help. > >> Any suggestions would be apreciated, but I have at least one specific >> question: Is an oscilator on the PIC neccesary for programming? For >> reading the Device ID? > > definitely not (twice). > > did you ground the LVP pin? is your power OK and decoupled? > > -- > > Wouter van Ooijen I think I figured it out, it looks like I've got two different types of issues. I believe the shifted ID is a self inflicted problem from the application circitry that's attempting to share PGC / PGD. It includes a pulldown resistor and a TVS to ground on both pins. I suspect the TVS represents too much capacitance and is causing issues. I removed them and now two of my four units seem to work fine. The other two still report all 1s, but since only 2 of the 4 are doing this, the likely cause is quite different. Thanks for the capacitor suggestion (you too, Olin), it doesn't seem to have been the problem in this case, but it got me thinking in the right direction. Since you mentioned it: I'm using a HV programmer and didn't think I needed to ground LVP?? (But even if I did, application circuitry on that pin includes a 2k pulldown resistor.) Thanks, -Denny --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .