SNP is documented in the GE manual "Series 90 PLC Serial Communications" (GFK-0582B). If you're going to be using this from Visual Basic or some other desktop operating system, I would recommend purchasing an ActiveX control. It'll save you time, be less frustrating, and probably much more reliable. If you don't have the documentation for the protocol, I wouldn't even try throwing together some source you found on the net -- you'll have no idea what's going on. In my opinion, the only people pulling out the books and writing code should be those (like me) who can't technically use ActiveX controls or are trying to squeeze every last little KB out of their code.
