The output of
$ mc ncp show circ ewa-0 char
will tell you whether it worked: the attribute service must have the value enabled.
If that is not the case check:
$ mc ncp list circ ewa-0 char
The service enabled value must be present and reboot the system to make it effective.
You'll see decnet opcom messages only on OPA0 or on a terminal where the command $
REPLY/ENABLE was entered. Hans