Garmin MX20 Installation Manual - A.1   Moving Map Input

I/O Specifications 

MX20 Installation Manual 

 A-1 

APPENDIX A - I/O Specifications  

This appendix includes the RS-232 serial port interface specifications. 

A.1   Moving Map Input 

The format of the moving map data output is shown below. Definitions of the input data is included in 

Table A-1 and Table A-3.  A sample output message is included in Figure A-1. 

Baud rate: ............................................... 9600 

Data bits: ................................................ 8 

Stop bits: ................................................ 1 

Parity:  .................................................... none 

Output rate: ............................................ approx. 1 seconds 

Message length: ..................................... variable, approx. 83 to 484 characters 

The serial output messages are in the following format. 

...

  ................................................... ASCII “start of text” character (1 byte, 02h) 

........................................................ item designator (1 byte, from following table) 

.................................................... item data (format listed in following table) 

........................................................ item terminator (1 byte, 0Dh) 

 ................................................... ASCII “end of text” character (1 byte, 03h) 

Table A-1.  Moving Map ASCII Navigation Data 

ID Data 

Format 

Length 

Description 

A sddmmhh 

9 Present 

latitude 

   s =sign: N for north, S for south 

   dd = degrees 

   mm = minutes 

   hh = hundredths of minutes 

B sdddmmhh 

10 Present 

longitude 

   s = sign: E for east, W for west 

   ddd = degrees 

   mm = minutes 

   hh = hundredths of minutes 

C 

ddd 

3 

Track (magnetic): ddd = degrees 

D 

ddd 

3 

Ground speed: ddd = knots 

E 

ddddd 

5 

Distance to active waypoint: ddddd = nm x 10 

G 

sdddd 

5 

Cross track error: 

   s = sign: R for right, L for left of course 

   dddd =  distance off course, hundredths of nm 

I 

dddd 

4 

Desired track (magnetic): 

   dddd = degrees x 10 

K 

ddd[dd] 

3 to 5 

Active waypoint identifier: 

   ddd[dd] = ASCII waypoint identifier 

L 

dddd 

4 

Bearing to active waypoint (magnetic): 

   dddd = degrees x 10 

Q sddd 

4 Magnetic 

variation: 

   s = sign: E for east, W for west 

   ddd = degrees x 10 

T 

---A----- 

9 

Warnings: The 4th character will be an “A” when the 

navigation data is flagged, otherwise, all characters will be 

dashed. All other navigation data will be dashed when it is 

flagged.