I've never actually etched my own boards, just engineer something in eagle and proto it.
I probably should make this a wiki so that people can understand the chain of command on the turbo. The Holset VGT's have 2 plugs, 1 4pin & 1 2pin (in a 3 pin housing).
The 4 pin is the main connector, it is power / ground / can low / can high
The 2 pin is the VR sensor connector, it is VR+ and VR-
When talking to the turbo, it doesn't do anything on its own, except when it hasn't received a canbus command for a vein position, it will default to vein position 0 if it hasn't received a message in 5-10ms.
You can only talk to the turbo through canbus, and there is some other communication information, Steed knows some info I don't know if he will join.
Only 2 things I know that you can tell the turbo to do is,
Vein position
Re-calibrate position (this one is wonky sometimes the turbo shuts off afterwards sometimes nothing)
From what Steed told me, what the turbo can tell you is
Feedback from backpressure (some type of measurement the motor force used to maintain position of sorts)
Some turbos have a temperature probe ??
So in a sense, just talking to the turbo its only 1 direction, but CANBus is basically like your old vampire coax networks, where everything is connected, has addresses, but its more modern in that, you designate what you want to talk to, and everything hears it but only the appropriate device will respond given that the command you send is good.
The VR sensor is a plug all on its own, completely independent of the controller housing. I imagine some manufactures use it, but most likely a lot have a harness connection that goes no where.