I wrote a bootloader ROM. The ROM user Address space 0000-2000h. When you select run on the menu, it jumps to 8000h. Any interrupts etc it receives vectors to the correct offset from 8000h so everything works fine. It also has RAM tests/ Serial tests and the like. It is hard coded at 19200 baud, uses the serial port. My development board even switches the serial port between run and program mode, so you don't have the hassle of physically switching cables - what a relief!!