Data. - Garmin GNS 480 Installation Manaul

Appendix B - Serial Interface Specifications
B.1.1 Altitude Encoder/Converter Input
The GNS 480 will accept various serial altitude formats. The only configuration required for the altitude
encoder input is the baud rate – the serial altitude format will be recognized automatically. The input
signals shall be compatible with RS-232C and have the following characteristics:
Baud rate: ...............................................1200/9600 (defined by encoder used)
Data bits: ................................................8
Stop bits: ................................................1
Parity: .....................................................none
Expected input rate: ...............................approx. 1 second
Message length: ......................................17 characters
B.1.1.1 Apollo Altitude Format
The Apollo (IImorrow) altitude format is 1200 baud with a message length of 17 characters, as defined in
Table B-2. Several sample messages are illustrated in Figure B-1.
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
B-2
Table B-2. 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.
indicating that the altitude is outside specified range of
the encoder.
560-0982-01 Rev L GNS 480 (CNX80) Installation Manual