Garmin GNX 20 User manual

GNX™ 20/21 Installation Instructions
To obtain the best possible performance, install this marine
instrument according to these instructions. If you experience
difficulty during the installation, contact Garmin® Support, or seek
the advice of a professional installer.
This instrument communicates with NMEA 2000® sensors and
devices, and shows information such as speed, heading, and
water depth when connected to the appropriate sensors. The
instrument can also communicate with a NMEA® 0183 device
using an optional data cable.
Important Safety Information
WARNING
See the Important Safety and Product Information guide in the
product box for product warnings and other important
information.
CAUTION
To avoid possible personal injury, always wear safety goggles,
ear protection, and a dust mask when drilling, cutting, or
sanding.
NOTICE
When drilling or cutting, always check what is on the opposite
side of the surface to avoid damaging the vessel.
Mounting Considerations
NOTICE
This device should be mounted in a location that is not exposed
to extreme temperatures or conditions. The temperature range
for this device is listed in the product specifications. Extended
exposure to temperatures exceeding the specified temperature
range, in storage or operating conditions, may cause device
failure. Extreme-temperature-induced damage and related
consequences are not covered by the warranty.
The mounting surface must be flat to avoid damaging the device
when it is mounted.
When selecting a mounting location, observe these
considerations.
• The mounting location should be at or below eye level to
provide optimal viewing as you operate your vessel.
• The mounting location should be at less than a 45° viewing
angle for the GNX 20 Marine Instrument with Standard LCD
and less than a 50° viewing angle for the GNX 21 Marine
Instrument with Inverted LCD. Screen color inversion occurs
when the viewing angle is greater than 30° in the 9 o'clock
direction on the GNX 20 and when the viewing angle is
greater than 60° in the 1 o'clock direction on the GNX 21.
• The mounting surface must be strong enough to support the
weight of the device and protect it from excessive vibration or
shock.
• To avoid interference with a magnetic compass, the device
should not be installed closer to a compass than the
compass-safe distance value listed in the product
specifications.
• The area behind the mounting surface must allow room for
the routing and connection of the cables.
Mounting the Device
NOTICE
If you are mounting the device in fiberglass, when drilling the
pilot holes, use a countersink bit to drill a clearance counterbore
through only the top gel-coat layer. This will help to avoid
cracking in the gel-coat layer when the screws are tightened.
The included template and hardware can be used to flush mount
the device in your dashboard.
1Trim the flush-mount template and ensure it fits in the
location where you plan to mount the marine instrument.
The flush-mount template is included in the product box.
2Remove the liner from the adhesive on the back of the
template and adhere it to the location where you plan to
mount the marine instrument.
3If you plan to cut the hole using a rotary tool instead of a
90 mm (3.5 in.) hole saw, use a 10 mm (3/8 in.) drill bit to drill
a pilot hole to begin cutting the mounting surface.
4Using the 90 mm (3.5 in.) hole saw or rotary tool, cut the
mounting surface along the inside of the dashed line
indicated on the flush-mount template.
5If necessary, use a file and sandpaper to refine the size of
the hole.
6Place the marine instrument into the cutout to confirm that
the mounting holes on the template are in the correct
locations.
7If the mounting holes are not correct, mark the correct
locations of the mounting holes.
8Remove the marine instrument from the cutout.
9Drill the 2.8 mm (7/64 in.) pilot holes.
If you are mounting the marine instrument in fiberglass, use a
countersink bit as advised in the notice.
10Remove the remainder of the template.
11Place the included gasket on the back of the device and
apply marine sealant around the gasket to prevent leakage
behind the dashboard.
12If you will not have access to the back of the device after you
mount it, connect all necessary cables to the device before
placing it into the cutout.
NOTE: To prevent corrosion of the metal contacts, cover
unused connectors with the attached weather caps.
13Place the marine instrument into the cutout.
14Securely fasten the marine instrument to the mounting
surface using the supplied screws.
If you are mounting the marine instrument in fiberglass, use a
anti-galling lubricant as advised in the notice.
15Snap the bezel into place.
GUID-E313CF8B-397D-48AF-8839-977C29E188D5 v4August 2020

Connection Considerations
The marine instrument connects to power and to data sources
through a NMEA 2000 network.
Although the instrument cannot directly receive NMEA 0183
data, it can display NMEA 0183 data from sources connected to
a GNX 20 or GNX 21 device (sold separately) on the same
NMEA 2000 network.
The instrument can also receive data from Nexus® instruments
and sensors using a GND™ 10 device (sold separately).
NMEA 2000 Connection Considerations
NOTICE
If you are connecting to an existing NMEA 2000 network,
identify the NMEA 2000 power cable. Only one NMEA 2000
power cable is required for the NMEA 2000 network to operate
properly.
A NMEA 2000 Power Isolator (010-11580-00) should be used in
installations where the existing NMEA 2000 network
manufacturer is unknown.
If you are installing a NMEA 2000 power cable, you must
connect it to the boat ignition switch or through another in-line
switch. NMEA 2000 devices will drain your battery if the NMEA
2000 power cable is connected to the battery directly.
The marine instrument connects to a NMEA 2000 network on
your boat. The NMEA 2000 network provides power to the
marine instrument and data from NMEA 2000 devices such as a
wind sensor. The included NMEA 2000 cables and connectors
allow you to either connect the device to your existing NMEA
2000 network or create a basic NMEA 2000 network if needed.
If you are unfamiliar with NMEA 2000, you should read the
“NMEA 2000 Network Fundamentals” chapter of the Technical
Reference for NMEA 2000 Products. To download the
reference, go to garmin.com/manuals/nmea_2000.
Wind transducer
GND 10 black box bridge
Marine instrument
Ignition or in-line switch
NMEA 2000 power cable
NMEA 2000 drop cable
Power source
NMEA 2000 terminator or backbone cable
NMEA 2000 T-connector
NMEA 2000 terminator or backbone cable
NMEA 0183 Connection Considerations
• The marine instrument can receive NMEA 0183 data from
one device using a NMEA data cable (not included), but it
cannot transmit data from the NMEA 0183 device to the
NMEA 2000 network.
• If you are replacing a legacy Garmin marine instrument that
currently uses a NMEA data cable, you do not need to
purchase a new data cable, but you might need to replace
the quarter-turn locking ring with a threaded locking ring. See
your local Garmin dealer or www.garmin.com for more
information.
• The installation instructions provided with your NMEA 0183
compatible device should contain the information you need to
identify the transmitting Tx/A (Out +) and Tx/B (Out -) wires.
• When connecting NMEA 0183 devices with two transmitting
wires, it is not necessary for the NMEA 2000 bus and the
NMEA 0183 device to connect to a common ground.
• When connecting a NMEA 0183 device with only one
transmitting Tx (Out) wire, the NMEA 2000 bus and the
NMEA 0183 device must connect to a common ground.
• For extended runs, you should use at least 0.33 mm2
(22 AWG) wire.
• You must solder and seal all connections with heat-shrink
tubing.
Wire Color Wire Function
Red A red wire is present only on some variations of the data
cable, and should not be connected.
Black Accessory (-). This wire is used only when connecting the
marine instrument to a Garmin HVS GPS antenna.
Yellow Accessory (+). This wire is used only when connecting the
marine instrument to a Garmin HVS GPS antenna.
Blue Tx/A (Out +). This wire is used only when connecting the
marine instrument to a Garmin HVS GPS antenna.
2 GNX 20/21 Installation Instructions

Wire Color Wire Function
White Tx/B (Out -). This wire is used only when connecting the
marine instrument to a Garmin HVS GPS antenna.
Brown Rx/A (In +)
Green Rx/B (In -)
NMEA 0183 Connection Diagrams
This diagram is an example of a connection to a standard NMEA
0183 device with two Tx wires.
Item Description
Marine instrument with a NMEA data cable (not included)
Power source
NMEA 0183 compliant device
Item Garmin Wire
Function
Garmin Wire
Color
NMEA 0183 Device
Wire Function
N/A N/A Power
N/A N/A Data ground
Rx/A (In +) Brown Tx/A (Out +)
Rx/B (In -) Green Tx/B (Out -)
This diagram is an example of a connection to a standard NMEA
0183 device with one Tx wire.
Item Description
Marine instrument with a NMEA data cable (not included)
NMEA 2000 network (must connect to the same ground as the
NMEA data cable)
Power source
NMEA 0183 compliant device
Item Garmin Wire Function Garmin Wire
Color
NMEA 0183 Device
Wire Function
N/A N/A Power
N/A N/A Power ground
Rx/B (In -) Green Data ground
Rx/A (In +) Brown Tx
This diagram is an example of a connection to a Garmin HVS
GPS antenna.
Item Description
Marine instrument with a NMEA data cable (not included)
Power source
Garmin HVS GPS antenna
Item Marine Instrument Wire Color Antenna Wire Color
N/A Red
Black Black
Yellow Orange
Blue White
White White/orange
Brown Gray
Green White/red
Specifications
Specification Measurement
Dimensions without sun cover
(H×W×D)
110 x 115 x 30 mm (4.33 x 4.53 x
1.18 in.)
Dimensions with sun cover
(H×W×D)
115 x 120 x 35.5 mm (4.53 x 4.72 x
1.40 in.)
Weight without sun cover 247 g (8.71 oz.)
Weight with sun cover 283 g (9.98 oz.)
Temperature range From 5° to 158°F (from -15° to 70°C)
Compass-safe distance 209 mm (8.25 in.)
Material Case: fully-gasketed polycarbonate,
waterproof to IEC 60529 IPX7
standards
Lens: glass with an anti-glare finish
Brightness 1200 cd/m2 (NIT)
Power usage 3 W max
Unit max. voltage 32 Vdc
NMEA 2000 input voltage 9 to 16 Vdc
NMEA 2000 load equivalency
number (LEN)
7 (350 mA at 9 Vdc)
NMEA 2000 PGN Information
Transmit and Receive
PGN Description
059392 ISO acknowledgment
059904 ISO request
060928 ISO address claim
61184 Product information
126208 NMEA: Command, request, and acknowledge group function
126996 Product information
Transmit
PGN Description
126464 Transmit PGN list group function
Receive
PGN Description
126992 System time
127245 Rudder
127250 Vessel heading
127488 Engine parameters: Rapid update
127489 Engine parameters: Dynamic
127508 Battery status
128259 Speed: Water referenced
128267 Water depth
GNX 20/21 Installation Instructions 3

PGN Description
129025 Position: Rapid update
129026 COG and SOG: Rapid update
129029 GNSS position data
129283 Cross track error
129284 Navigation data
129285 Navigation route and waypoint info
129539 GNSS dilution of precision (DOP)
130306 Wind data
130310 Environmental parameters
130311 Environmental parameters
130312 Temperature
130313 Humidity
130314 Actual pressure
NMEA 0183 Information
When connected to an optional NMEA 0183 compatible device,
the instrument can receive these NMEA 0183 sentences.
Sentence Description
BOD Bearing (origin to destination)
DBT Depth below transducer
DTM Datum being used
DPT Depth
GGA Global positioning system fix data
GLL Geographic position (latitude and longitude)
GRMB GPS data
GRME GPS position error data
GSA GNSS DOP and active satellites
GSV GNSS satellites in view
HDG Heading, deviation, and variation
HDM Heading, magnetic
HDT Heading, true
MDA Meteorological composite
MTW Water temperature
MWD Wind direction and speed
MWV Wind speed and angle
RMB Recommended minimum navigation information
RMC Recommended minimum specific GNSS data
THS Heading sensor data
VHW Water speed and heading
WPL Waypoint location
XTE Cross track error
You can purchase complete information about National Marine
Electronics Association (NMEA) format and sentences from:
NMEA, Seven Riggs Avenue, Severna Park, MD 21146 USA
(www.nmea.org)
© 2014 Garmin Ltd. or its subsidiaries
Garmin®, the Garmin logo, and Nexus® are trademarks of Garmin Ltd. or its subsidiaries,
registered in the USA and other countries. GNX™ and GND™ are trademarks of Garmin
Ltd. or its subsidiaries. These trademarks may not be used without the express
permission of Garmin.
NMEA®, NMEA 2000®, and the NMEA 2000 logo are registered trademarks of the
National Marine Electronics Association.
© 2014 Garmin Ltd. or its subsidiaries support.garmin.com