[Gmecm] 16212488 ALDL MODE2/MODE3 bin dumping?

[Stefan Engh]

Hello everyone,
This is my first post to the list. I hit myself daily for not having woken up to this EFI stuff at least ten years ago! Playing catch-up is reeking havoc with my beauty sleep ;-)
 
It all started about two years ago when I bought a 1995 6.5TD Suburban (ECM 16212488) and found out there where no PC scan tools available. I started developing one for myself. It's called GMTDScan and has been out for almost a year now. The last couple of days I've been playing with adding a ALDL MODE2/MODE3 bin dump feature to it. I figured it would be a good way to harvest stock bins from the 1994-95 6.5TD. Here's where I am having problems...
 
I can only get it to dump addresses $4000-$FFFF. Trying to dump anything above $4000 only returns the value of last byte ($FFFF).
Could someone please shed some light on why it works that way?
What type of information is stored in the $0000-$3FFF address range?
 
/Stefan