(The code was on TRS-80 floppy disks, and I need to recover it so that I can post it here.)
I actually bought a 4K CoCo for $400 just so I could write 6809 assembler code. I implemented a Forth interpreter on it, but that was before I had a disk drive, so it's on a cassette tape in a box somewhere.
This is a full-screen debug monitor program with single-step trace and a disassembler. The look of it was based on the old TRSDOS debugger.
cdebug9.asm (original version)
cdebug9.txt (with some comments added back in 2004)
I wrote this because I had disassembled the interpreter from the TRS-80 Model III version of Zork I. I even tested it by playing through the whole game before I had written the save and load commands. It was six months later that Infocom finally advertised their own Color Computer version.