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

I/O Specifications
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
Byte Data Format
1 "#"
2 "A"
3 "L"
4 " "
5 "+" or "-"
6-10 ddddd
11 "T"
12 "+" or "-"
13-14 dd
15-16 dd
17 <CR>
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
"-09981" ................................................. Possible hardware problem: expected from encoder
"-09982" ................................................. Altitude out of range: expected from the encoder indicating
A-6

Table A-5. Altitude Input Data

Description
ASCII "#" (023h)
ASCII "A" (041h)
ASCII "L" (04Ch)
ASCII space (020h)
Altitude sign: ASCII "+" or "-" (02Bh or 02Dh)
Altitude in feet, right justified with leading zeros
ASCII "T" (054h)
Temperature sign: ASCII "+" or "-" (02Bh or 02Dh)
Internal altimeter temperature
Checksum of bytes 1 through 14, computed in hex, output in
ASCII format (i.e., "FA" hex)
ASCII carriage return (0Dh)
there is a loss of signal from the encoder.
indicating a temperature greater than 55 C or if data is
invalid.
that the altitude is outside specified range of the encoder.
560-1025-09 Rev E MX20 Installation Manual