Christopher / James I'll try a partition, just to see if it does make a difference to what seems to be a fairly predictable card read error. Maybe I just got unlucky with a dodgy pathway at the bottom end of the card Also, I'm making up a 512kB SRAM board. A TC554001, 4040 and 18F2520. Originally for files but coincidentally the size of a card data block. I will try some experiments to see if occassional re-writes, rather than a format/reload, resets whatever is happening in the controller. If it doesn't, well I can still use it for the files and now I have a board layout for a datalogger or whatever Thanks Joe ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2015.0.5751 / Virus Database: 4311/9339 - Release Date: 03/19/15 --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .