I'm only confirming here, fellas, what sup8pdct advised over on Atari Age the other day, as I tested the one Brenski sent me (I did film it but have managed to delete it - standby for a replacement clip when I get a mo, once the 800 has been packed away ready for despatch to Thark), and this advice WORKS (PSU required? Try the standard 9v 1050 PSU and you should be good to go)- it's solid gold - so thank you, sup8pdct...
...to test if something is working with 850, turn off everything, turn on 850 then turn on computer, no disk drives , sio2sd etc devices powered on.
You should hear after a few command frame fails, 2 or sector size beeps then a big long beep. That sound is the rs232 driver loading in to computer from 850. It can also be loaded from dos via a small program stored on disk.
The rs232 driver is not required for the printer port.
ABOVE: Testing your 850 is as easy as following the advice in the quote box-out above. As for ever connecting a teletype, centronics printer or dumb terminal to my 850, I would guess those are all long-shots, but one of these days, the shell might house something like an SIO2PC.
Will upload my test vid the minute I get round to also field-testing and comparing the Koala Pad versus Atari's Touch Tablet... and of course the add on keypad the CX85.