While I couldn't find an online copy as well, so I had to check the dead tree issue :) It won't make you happy, as there is no sophisticated example given. Only two rather simple flow diagrams and a dotzend instructions loading the registers. Most text is spend repeating the datasheet.
Then again it shouldn't be a huge task to get a 6850 running. It is a no frills serial port. Everything needed is nicely described in the datasheet. There are no suprises.
There are countless examples out there how to use, like in Leventhal's 6809 Assembly book. Its examples are similar to the ones in the app-note. You might as well want to check the manuals for the boards you have, as Motorola used to provide rather detailed manuals. In fact, Leventhal did as well write books for some Motorola boards, like Experimentation with the Motorola MEK 6800D2, which goes into greater detail than the app-note.
Of course, if your problem is more exotic than straight serial communication, why not post a question about?