Garmin G3X Touch Pilot's Manual page 157

GROUND MODE
Ground Mode is normally selected automatically when the aircraft is on the ground.
The transponder powers up in the last mode it was in when shut down. A green GND
indication and transponder code appear in the mode field of the Transponder Data
Box. In Ground Mode, the transponder does not allow Mode A and Mode C replies,
but it does permit acquisition squitter and replies to discretely addressed Mode S
interrogations.
STANDBY MODE (MANUAL)
In Standby, the transponder does not reply to interrogations, but new codes can be
entered. When Standby Mode is selected, a white STBY indication and transponder
code appear in the mode field of the Transponder Data Box. When in Standby Mode,
the transponder will not auto transition to any mode based on phase of flight.
MANUAL ON MODE
ON Mode can be selected at any time. ON Mode generates Mode A and Mode S
replies, but Mode C altitude reporting is inhibited. In ON Mode, a green ON indication
and transponder code appear in the mode field of the Transponder Data Box.
ALTITUDE MODE (AUTOMATIC OR MANUAL)
NOTE: The automatic transition to ALT Mode only occurs from the STBY Mode
on the transponder.
If the transponder is configured with Automated Airborne Determination, ALT Mode
is automatically selected when the aircraft becomes airborne. When the aircraft is on
the ground, the transponder automatically selects and displays STBY. ALT Mode may
also be selected manually.
If Altitude Mode is selected, a green ALT indication and transponder code appear
in the mode field of the Transponder Data Box, and all transponder replies requesting
altitude information are provided with pressure altitude information.
190-01754-00 Rev. L Garmin G3X Touch Pilot's Guide
CNS Interface
137