The 6809 is a binary-incompatible evolution of the previous 68xx series CPU. Often designed the “best 8-bit CPU of all times”, it prefigures some of the features that will make the 68000 a success.
This is already covered elsewhere on the internet. Do I need to repeat everything?
The 6809 interrupts fetch an address from memory, and jumps to it. The interrupt table is at a fixed address at the top of memory: