implements #21223
@mtr: I was not really able to test the "Test output" feature it on your system, because I constantly received ds485 timeout errors. I also had these errors when opening the dialog, there seems to be something wrong with your KM300.
I am still a bit confused about the strings that I should use (see ticket), I'll try to confirm with Jaime.
I was not sure if I should use setOutputValue or setValue JSON calls (see my e-mail).