I first compile and upload a IHX file to the loader program that runs when the board powers up. The last two bytes sent to the loader is the address of where to jmp to immediately after the uploading is complete.

What I wanted the program to do, was read a byte, then echo it back. On my computer I upload the ihx file, then the address 0x8000, which is the address of the external RAM chip on the board. Then the computer starts sending a stream of A's. It also tries to print out what it receives, which right now is nothing.

This might sound like a dumb question, but does the serial interrupt vector exist at absolute address 0x0023, even if my program runs at 0x8000? In other words, it won't exist at 0x8023. I wonder because the R0-R7 registers interfere with EXT0 vector at 0x0003, and the other interrupt vecotrs interfere with the default location of the stack starting at 0x08.

any help is appreciated...