Liam O'Hagan wrote: > is something taking a while to start up because of the cold? What sort of > oscillator are you using? It's driving a 4MHz crystal. The device at that point has been on (never sleeping) for at least a minute (the time to acquire the calibration) and to be sure I was at equilibrium it was actually running for about an hour before the first trial and probably 20 minutes the second time. Ken Pergola wrote: > It's not too clear what you are actually putting inside the freezer besides > the PIC -- is this a complete PCB board or a perf-board project? It's on a breadboard. Condensation did form later but was not present during the EEPROM writes. Either way I'm not sure how that would affect just the first EEPROM byte. The crystal is a junk box part labelled 4.000000 KDS 2K. I can't find any KDS crystal datasheets. It ran the rest of the chip fine, though. Jinx wrote: > First, are you sure you've got the industrial or better grade PIC ? It's an 18F2320, as far as I can tell it only comes in Industrial (-40C..85C) and Extended (-40C..125C). I have an industrial one. Both should go down to -40C, and I was only at -20C at worst (probably a bit warmer). > Are you using SLEEP and WDT at all ? 32kHz ? No, device was awake for an hour for one trial. Not using a watch crystal. > WDT can be 25% faster at -18C than at 25C and I wonder if there's > some problem allowing enough time for the PIC's oscillator to wake My pet theory is that the internal charge pump to program the EEPROM takes longer to start. I was hoping someone would know if setting WREN starts it so I could 'warm it up'. -- Ben Jackson http://www.ben.com/ -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads