I've probably used 10 different valve positioners over the years, and every one has had
- 4-20mA input control signal
- mechanical linkage to read the valve position for feedback
The full open or full closed limit switches are sometimes an optional module on the positioner, other times the limit switches are stand-alone options. The limit switches typically are feedback to the control system DI, not a position DI.
Most have had a Digital input option, typically to force the positioner to a given state or as an input for a valve proving cycle.
The specific functionality of a digital input would require research.
Siemens uses 2 piezo valves to source air to the actuator ports, not sure if others do or not.