Create a new thor, right click on any of unused space on the synth, and choose "Initialize Patch" from the drop-down menu. You should have the synth expanded so that you can see the programmer. The default oscillator (at the top-left of the programmer) will be a pure saw wave.
This sound was used on some early systems, but the more commonly used waves are the square and triangle waves. These pure waves should be able to cover a ton of expressive range by themselves, but you stay well within the motif if you add a light "soft clip" or "hard clip" in the middle panel. Also, don't be afraid to add some light chorus effect. The older NN sampler has some great raw synth sounds pre-packaged too.
The oscillator drop-down menus leave the option for "Noise" generation as well. These can be manipulated for chiptune drum sounds and percussion.
I got some good samples for free here:
http://www.boyinaband.com/2009/09/free-sample-pack-%E2%80%93-33-chiptune-samples/. I've just saved a set of them in a custom Redrum patch for quick access.
There's some quick notes, at least. Hope that gives some direction.
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