Avidyne IFD540 Pilot's Manual page 162

Nav Source
State
OBS VLOC

NOTE
Aircraft Integration
The Nav Source modes available in your airplane
will be dependent on the level of integration with
other on-board systems. Avidyne strongly
recommends practice operations in VMC conditions
before any use in IMC, to understand the level of
integration between the IFD and the other on-board
systems and therefore the Nav Source modes
available.
The nav source knob is labeled "CDI" above the knob and is
designed to allow you to toggle the CDI and system nav source
between the active and armed states defined above.
5-6 Navigation
OBS becomes the active state and VLOC is
the armed state. Deviation data being
transmitted by the IFD is reactive to the
external course setting knob (or the Nav
Source knob if no external course control is
present) for the inbound/outbound course.
Note that this state is accessed by pushing in
the Nav Source knob and then it takes the
place of GPS

earlier in this table.
Description
VLOC mode as described