Garmin MX20 - Altitude Encoder;Converter Input; Table A-5. Altitude Input Data

I/O Specifications
A-6 560-1025-09 Rev E MX20 Installation Manual
A.4 Altitude Encoder/Converter Input
The format of the altitude input is as follows. Definition of the input message is included in Table A-5.
Several sample messages are illustrated in Figure A-3.
Baud rate: .............................................. 1200
Data bits: ............................................... 8
Stop bits: ................................................ 1
Parity: .................................................... none
Expected input rate: ............................... approx. 1 second
Message length: ..................................... 17 characters
Table A-5. Altitude Input Data
Byte Data Format Description
1 “#” ASCII “#” (023h)
2 “A” ASCII “A” (041h)
3 “L” ASCII “L” (04Ch)
4 “ “ ASCII space (020h)
5 “+” or “-” Altitude sign: ASCII “+” or “-” (02Bh or 02Dh)
6-10 ddddd Altitude in feet, right justified with leading zeros
11 “T” ASCII “T” (054h)
12 “+” or “-” Temperature sign: ASCII “+” or “-” (02Bh or 02Dh)
13-14 dd Internal altimeter temperature
15-16 dd Checksum of bytes 1 through 14, computed in hex, output in
ASCII format (i.e., “FA” hex)
17 <CR> ASCII carriage return (0Dh)
The altitude input can decode several status or error codes. These codes would be in place of the altitude
data in characters 5 - 10 as follows.
“-09980” ................................................. Heater not ready: expected during encoder warm-up or if
there is a loss of signal from the encoder.
“-09981” ................................................. Possible hardware problem: expected from encoder
indicating a temperature greater than 55C or if data is
invalid.
“-09982” ................................................. Altitude out of range: expected from the encoder indicating
that the altitude is outside specified range of the encoder.