As mentioned in a previous post, Bill Grundmann has been documenting his investigation into Canons E-TTL protocol. Bill has just released a PDF summarising what he has found so far.
I’ve yet to go over it in detail, but for those looking at doing some E-TTL investigation of their own this document is a must.
http://billgrundmann.files.wordpress.com/2009/03/ettl_grundmann.pdf
PDF 