Avidyne IFD540 Pilot's Manual page 23

COOL FEATURE
Decoded Agency Identifier
The agency (e.g. Clearance Delivery, Ground,
Tower, Approach, etc) for the Active and each
displayed Standby com frequency are displayed in
each com frequency slot. This is a handy reminder
of the agency to which you have tuned in each slot.
Similarly, if the frequency displayed is a nav
frequency, then the Morse code decoded identifier
will be displayed and will stay displayed for as long
as the IFD can decode the Morse code, which
serves as a usable means to Tune-Identify-Monitor.
If a slot is receiving a voice transmission, a "RX" indication will be
displayed along the right edge of the given com slot.
When the active frequency is transmitting, a "TX" indication will
be displayed along the right edge of the Active com slot.
Tuning
Tuning can be accomplished through several methods.
Whichever frequency slot has been selected as the #1 Standby
can be manually tuned by twisting the bottom left knob on the
bezel. The outer ring changes the digits to the left of the decimal
point and the inner ring changes the digits to the right of the
decimal point. The slot being tuned this way is highlighted in
reverse video as depicted in the 126.000 example below.
Manual Com/Nav Tuning Reverse Video Depiction
System Overview 1-17