Hello Steve, Jay, and Peter,

Thank's for your help.. I've decided to take the old boot-strap approach coupled with a nifty bit of automatic memory remapping (using a simple 74154!!) to allow the upper 32k of Program Memory (implemented with an Atmel AT28C256 JEDEC Flash) to be temporaily mapped into the upper 32k of RAM space (used by the various bits of I/O) for writing.. and then switched back into the upper 32k program memory space. This will leave me with 32k of ISP program space, and 32k of unchangeble program space (also an AT28C256, but programmed out of system).. This leaves me with the disadvantage of not being able to reconfigure where the interrupt vectors jump to (unless I sacrifice a few machine cycles by making them first jump to a second set of vectors in the upper 32k) and the loss of one I/O pin (used to re-map the memory arrangement).. still, I can implement the my operating-system and BIOS into the lower 32k (where most interrputs will be handled anyway) and program the upper 32k using my own multi-node interface (using BIOS routines in the lower 32k). I'm happy to give details to anyone who wants them.

Oh, and by the way, Steve and Jay, stop having a conversation in MY subject folder ;-)

Bye for now.

Oh yeah, Steve if you read this, do you know anywhere where I can get details on using a Dual Port RAM.. I've got a few data sheets, but I don't quite understand what the Semaphore pin is for.. I know you're using Dual-Port RAM in one of your apps (which one?), and I want to use it in my video project..