Depends on the ecu in use.
Aftermarket stuff simply uses a similar method and a pulse system to vary the air pressure avaiulable at the wastegate capsule. This is EXACLY how most Ecu's work, but some of teh jap stuff has more definable targets such as peak scramble etc etc..

The jap stuff has the advantage of being user controllable, although with many customers i fail to see that as an advantage and see it more as a danger point