[aprssig] Dear Mr Kenwood (MicE decoding)

Robert Bruninga bruninga at usna.edu
Mon Dec 28 17:21:28 CST 2009

>> Decoding the Mic-E format is very simple, 
>> and especially in a pic chip.  A simple offset 
>> subtraction of the binary value of the Mic-E 
>> character yields the numeric value of latitude or
>> longitude etc...
> "Especially in a PIC chip?"  How do you figure?

Six bytes of Latitude: (0-9 or A-J or P-Y)
1) If > "9" then set the approprate msg/flag bits
2) If > $70 then Subtract $70 hex from the byte.  
3) If > "@" then subtract $41 hex from the byte
3) Result is decimal digit of latitude. Done

Base91 Encoding of Longitude:
1) for each byte, subtract 28 decimal
2) result is two digits of longitude.
3) do 3 times. 
4) Add 100 degrees if 100 degflag is set
5) Subtract 60 if minutes digits are > 60

Done.  Plus a little cleanup here and there...  It was designed
to be a pretty simple manipulation of bits.  A table was never
intended.  That was just how Ian decided to represent the
algorithm in the spec making it appear overly complex when in
fact, it is a very simple offset of bits.

Bob, Wb4APR

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