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

Display-digit functions:

Indicating own squawk code (mode-A reply): menus 0,1,2,3,4 or
indicating TCAS mode + distance, alternating threat squawk/FL: menu 5 or
indicating own transponder mode and flight level: menus 6,7,8,9.

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).
Central decimal point blinking: TCAS interrogation transmission.
All three decimal points on: internal error (PLL unlock at power-on).
Power-on voice message: "POWER-ON TEST".

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: TCAS mode + distance, alternating threat squawk/flight level.
TCAS mode 0: TCAS off (standby, independent from transponder operation).
TCAS mode A: interrogating threat squawk code.
TCAS mode C: interrogating threat flight level (normal operation).

When a valid transponder reply is received within the TCAS range (11nmi),
the measured distance from the threat is displayed after the operating mode
as tens, units, decimal point and tenths of nautical miles. The distance
display alternates with the received threat squawk code or flight level,
depending on the TCAS interrogation mode. A three bar "---" display means
the threat is not sending pressure-altitude data. An additional segment "E"
in the distance tens digit indicates a reply with IDENT or a corrupted reply
(overlapping replies from more than one threat). The distance is always
measured from the nearest threat.

When the measured TCAS distance is less than 1.5 miles, a voice warning
is repeated: "TRAFFIC ONE MILE", "TRAFFIC HALF MILE", "TRAFFIC QUARTER MILE"
or "TRAFFIC VERY CLOSE". When valid altitude information is received from
the threat, its flight level is compared with the own flight level and one
of the following warnings are added: "HIGH" (threat more than 500ft higher),
"SAME LEVEL" (treat at about the same altitude) or "LOW" (threat more than
500ft lower). 

Menu 6: selecting the transponder operating mode (independent from TCAS).
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 (altitude encoder not operating).
Modo E: emergency mode, altitude encoder inactive, the flight
level set in menus 7,8,9 is being broadcast (to be used only
in the case of altitude-encoder failure) and is also being used for
TCAS altitude comparison.

Menus 7,8,9: 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).