Ports
Com - "common" port that can be switched to pass air from NO or NC
NO - normally open port. When the solenoid is OFF, air passes from Com to NO (or the other way - it's not a diode ;) )
NC - normally closed port. When the solenoid is ON, air passes from Com to NC
Port connections
Com is connected to the boost source (ie the inlet manifold)
NO is connected to the actuator
NC is connected to fresh air (in a MAP/AlphaN car. MAF is slightly different...)
Yet to be re-edited
You then have a duty cycle table (TPS against RPM) and this is used to stop the actuator "seeing" pressure. When you want to build boost fast, the duty cycle approaches 100%.
The "sense" of this changes slightly for an external wastegate as these have a 2 port actuator - one for "open" and one for "hold closed". I will throw some diagrams together if you like...
[dnb]
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More info about boostcontrol, even plumbing diagrams, look at the the following page: BoostController - DB