Hi, I have tried to read/write to a x24F128S EPROM, I think it is referred to as I2C, but have never worked out from previous posts what the acronym is for. I tried my own code, unsuccessfully, then tried code from the list again unsuccessfully. I never get a ACK and reasonably confident that the pic is driving the port properly as I tested it using a parallel port capture program. The device X24F128S is a 3.5 volt device (I have easy access to these and not the 5 volt versions). I use a 2k resistor between the PIC port and the EPROM and have separate power supply for the PIC and EEPROM which is commoned to both. Should this be ok or does it sound like this is my problem. If I can be confident this is NOT causing the problem I will continue trying to fix it, thou I feel I have exhausted all possible problems. Regards Justin -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads