Hi, I am, in my "spare" time re-rwiting the Hitex C51 Primer for it next edition (4th) and first major revision in nearly 10 years. An early draft V3.5 is on my personal web site http://Quest.phaedsys.org as a PDF Any comments or suggestions for subjects to be covered in Edition 4 are welcome. The version on the web site above will be regularly updarted and when complete it will be available from http://www.hitex.co.uk BTW There is a lot of other 8051 stuff on the main web site at http://www.phaedsys.org Regards Chris