OK, problem is solved I think... Made up a very short cable to go from my existing master board to a PicDem2 board, and just hard wired it in. I ended up shutting off interupts (which is OK for this application) and running it in a polled fashion (again, for this app its fine) and cleaned up the code and then started to get the address/data1/data2 correctly. I had the master just send down a sequential count and then I logged it to the buffer so I could review it every 100 transactions and not a single dropped transaction. So, made up a shorter cable...its still about 28" and pushed the same code to that device..same results. Couple of notes. First, on the picdem board, I had no pullups. I left the pullups on the target board. Didnt seem to make a difference, in that I wasn't losing data, but not sure about the signal integrity, didnt pull out the scope to look since it appears to be working. I believe the master is running at 100KHz but I need to go verify that, just for my own information. Second, when I rebuilt the cable, I am quite sure the ground was broken, so that in itself may have been the root cause (grrrrr). So, thanks for listening, advising and commenting. -Al Dario Greggio wrote: Bob Axtell wrote: > i2c is not famous for distance, 3' is longer than anything I ever did, > and i2c was designed for single-board TV designs- nothing outside of the > same PCB. Hi, I can say that I've been using up to some 8meters of UTP cable on I2c (TC74 sensors). I reduced the pull-ups down to 470ohm circa. Also, reduced the frequency to 15KHz or so. Others have reached the same distances. So, I guess that either you have big capacitance on your wires, or the problem lies somewhere else. -- Ciao, Dario -- ADPM Synthesis sas - Torino -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --------------------------------- We won't tell. Get more on shows you hate to love (and love to hate): Yahoo! TV's Guilty Pleasures list. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist