It really sounds like you need to get an old book from the late 70's about Programming Micro computers.
It sounds like you are thinking along the lines of a "program" that is running in a higher language. The 6800 is using what is referred to as machine language. The "C" in cat, exists in memory as an ASCII byte. It takes many line of code to go fetch that byte and then transfer it to an external device, usually through some kind of an I/O port. If it needs to go out to a serial device (a single transmission wire), it has to shift it out one "bit" at a time, which would require a loop of code.
Almost no way to see a fixed pattern with a scope. Read up on signature analyzers to see how a tech would trouble shoot a running circuit. And even then, it requires you lock the program into a know mode or condition so you know what "should" be happening as opposed to what actually is happening.
A0 through A16 form a 16 bit address word which is used to point to one specific byte in memory. D0 through D7 contain the data byte that is either going to be written or read from that memory location.