Software commands for S53MV transponder
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4-digit LCD + four pushbuttons: blue,white,black,red

Display-digit functions:

Indicating squawk code (mode-A reply): menus 0,1,2,3,4 or
indicating operating mode and flight level: menus 5,6,7,8.

Single digit blinking: parameter setting.
All four digits blinking: transmitting IDENT (20 seconds).
Colon blinking or on: reply transmission to radar interrogation.
First decimal point on: transponder inactive (standby).
All three decimal points on: internal error (PLL unlock at power-on).

Pushbutton functions:

Blue pushbutton (left): move cursor left (menu-1).
White pushbutton (left/center): increment parameter.
Black pushbutton (right/center): decrement parameter.
Red pushbutton (right): move cursor right (menu+1).
Simultaneous depression of red+blue pushbuttons: trasmit IDENT
for 20 seconds (same function in all menus).

Menu functions:

Menu 0: normal operation (after power-on).
White pushbutton: write configuration into EEPROM.
Black pushbutton: read configuration from EEPROM.

Menus 1,2,3,4: setting squawk code, the blinking digit can
actually be changed. Digit select with blue/red pushbuttons.
Digit increment/decrement with white/black pushbuttons.
Usual squawk setting code 2000 or 7000 for VFR flight.

Menu 5: selecting the operating mode of the transponder.
First digit blank and first decimal point on: trasponder inactive
(standby), altitude encoder operating.
Mode C: transponder in mode ALT (normal operation A+C).
Mode A: transponder in mode A (the flight level is missing).
Modo E: emergency mode, altitude encoder inactive, the flight
level set in menus 6,7,8 is being broadcast (to be used only
in the case of altitude-encoder failure).

Menus 6,7,8: manual setting of the flight level in the case of
altitude-encoder failure (only in modes A and E when the built-in
altitude encoder is inactive).