I don't suppose the #Commodore64 has something equivalent to the #AppleII PR#n/IN#n from BASIC? On an Apple II it's easy to redirect BASIC so it reads & writes to a serial port allowing remote control of the Apple II from another machine.
On my #C64 I've got a program loaded and I'd like to be able to dump the bytes in RAM out a serial port so I can check if any bytes are missing or the wrong value. I need to do it without stomping on the loaded program.