Software commands for S53MV glideslope & marker receiver
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4-digit LCD + four pushbuttons: blue,yellow,white,black

Display-digit functions:

Indicating GS frequency (3XX:XX MHz) or (ILS paired) LOC frequency
(1XX:XX MHz): menus 0,1,2,3,4 or
indicating marker received-signal strength, marker squelch setting and
marker volume setting: menus 5,6 or
indicating glideslope CDI and optionally glideslope signal strength: menu 7.

Single digit blinking: parameter setting.
Left decimal point: outer marker 400Hz tone decoder active.
Central decimal point: middle marker 1300Hz tone decoder active.
Right decimal point: inner marker 3000Hz tone decoder active.
All three decimal points on: internal error (temporarily PLL unlock
at power-on or at GS/LOC frequency switching).

Pushbutton functions:

Blue pushbutton (left): move cursor left (menu-1).
Yellow pushbutton (left/center): increment parameter.
White pushbutton (right/center): decrement parameter.
Black pushbutton (right): move cursor right (menu+1).
Simultaneous depression of blue+black pushbuttons: write GS/LOC
frequency into current memory number, marker squelch and marker volume
into EEPROM.

Menu functions:

Menu 0: standby (after power-on).
Yellow pushbutton: select next GS/LOC frequency in EEPROM.
White pushbutton: select previous GS/LOC frequency in EEPROM.
Memory number 0,1,2,3,4,5,6,7,8,9,A,b,C,d or E is shown while blue,
yellow or white pushbuttons are held depressed.

Menus 1,2,3,4: setting the GS/LOC frequency, the blinking digit
can actually be changed. Digit select with blue/black pushbuttons.
Digit increment/decrement with yellow/white pushbuttons.
First digit 0 or 1 indicates (ILS paired) LOC frequency (1XX:XX MHz).
First digit 2 or 3 indicates true GS frequency (3XX:XX MHz).
The hundreds MHz digit is assumed 1 or 3 and is never shown.

Menu 5: setting the marker squelch level "0-4". "0" squelch inactive,
"1" most sensitive marker squelch, "4" least sensitive marker squelch.
Also indicating marker received-signal strength "0-4" and marker volume
setting.

Menu 6: setting the volume level "0-8". "0" mute, "1" quietest, "8" loudest.
Also indicating marker received-signal strength "0-4" and marker squelch
setting.

Menu 7: indicating glideslope CDI and optionally glideslope signal strength.
Yellow pushbutton: enable glideslope signal strength display in first digit
(range 0-F). White pushbutton: all four digits used for GS CDI (normal
operation after menu change).

GS CDI operation:
Blinking colon only: glideslope signal level too low (0-2).
Four horizontal bars "----": GS center, signal level ok (3-F).
Additional 1-8 vertical segments above: below GS (150Hz>90Hz), climb.
Additional 1-8 vertical segments below: above GS (90Hz>150Hz), descend.
Four "oooo" above/below: overrange below-GS (150Hz) / above-GS (90Hz).