190-00885-07
GPS 17x HVS Technical Specifications
Rev. A
Page 9
4
GPS 17X HVS SOFTWARE INTERFACE
The interface protocol design of the GPS 17x HVS is based on the National Marine Electronics Association’s
NMEA 0183 ASCII interface specification. This standard is fully defined in
NMEA 0183, Version 2.30
. You can
obtain a copy of the latest specification from NMEA,
In addition to the standard NMEA 0183 sentences, the GPS 17x HVS may also be configured to transmit
information over their serial interface using NMEA 0183 compliant Garmin proprietary sentences. These proprietary
sentences begin with the characters, “$PGRM”, instead of the characters “$G” that are typical of the standard
NMEA 0183 sentences. The characters “$P” indicate that the sentence is a proprietary implementation and the
characters and “GRM” indicate that it is Garmin’s proprietary sentence. The letter (or letters) that follow the
characters “$PGRM” uniquely identifies that particular Garmin proprietary sentence.
It is also possible to configure the GPS 17x HVS to transmit binary data information over their serial interface. See
Appendix B: Garmin Binary Output Format
for details.
The following sections describe the NMEA 0183 data format of each sentence transmitted and received by the GPS
17x HVS.
4.1
RECEIVED NMEA 0183 SENTENCES
The following paragraphs define the sentences that can be received on the GPS sensor’s port. Null fields in the
configuration sentence indicate no change in the particular configuration parameter. All sentences received by the
GPS sensor must be terminated with <CR><LF>, the ASCII characters for carriage return (0D hexadecimal) and
line feed (0A hexadecimal). The checksum *hh is used for parity checking data and is not required, but is
recommended for use in environments containing high electromagnetic noise. It is generally not required in normal
PC environments. When used, the parity bytes (hh) are the ASCII representation of the exclusive-or (XOR) sum of
all the characters between the “$” and “*” characters, non-inclusive. The hex representation must be a capital letter,
such as 3D instead of 3d. Sentences may be truncated by <CR><LF> after any data field and valid fields up to that
point will be acted on by the sensor.
4.1.1
Almanac Information (GPALM)
The GPALM sentence can be used to initialize the GPS sensor’s stored almanac information in the unlikely event of
non-volatile memory loss or after storing longer than six months without tracking GPS satellites.
$GPALM,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>,<14>,<15>*hh<CR><LF>
<1>
Total number of ALM sentences to be transmitted by the GPS sensor during almanac download.
This field can be null or any number when sending almanac to the GPS sensor.
<2>
Number of current ALM sentence. This field can be null or any number when sending almanac
to the GPS sensor.
<3>
Satellite PRN number, 01 to 32
<4> GPS
week
number
<5> SV
health,
bits 17–24 of each almanac page
<6> Eccentricity
<7>
Almanac reference time
<8> Inclination
angle
<9>
Rate of right ascension
<10>
Root of semi major axis
<11>
Omega, argument of perigee
<12>
Longitude of ascension node
<13> Mean
anomaly
<14> af0
clock
parameter
<15> af1
clock
parameter
