Garmin Apollo CNX80 Installation Manaul - page 138
Appendix B - Serial Interface Specifications
B-2
560-0982-01 Rev L
GNS 480 (CNX80) Installation Manual
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.
Table B-2. 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
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.