Garmin G3X Installation Manual page 41

2.3.1.3.2 CAN Bus Wiring
Wiring used for the CAN bus should be shielded twisted-pair cable, MIL-C-27500 or equivalent. 22 AWG
or larger wire is recommended for physical robustness and ease of installation. The shields for each CAN
bus wire segment should be interconnected, forming a continuously connected shield from one end of the
CAN bus to the other (Figure 2-10 and
grounded to the device connector backshells at the two extreme ends of the bus, but it is acceptable to also
ground the shield at any or all other devices on the CAN bus.
CAN BUS TERMINATION CAN BUS TERMINATION
JXXX PXXX JXXX PXXX
CAN-H CAN-H
CAN-L CAN-L
SHIELD GROUND SHIELD GROUND
ALL WIRING SHOWN IS TWISTED SHIELDED PAIR ALL WIRING SHOWN IS TWISTED SHIELDED PAIR
For proper CAN bus operation, it is important for all devices on the CAN bus to share a common power
ground reference. Connect all LRU power ground pins to a single common ground point - do not use local
ground points or use the aircraft structure as a ground return path.
2.3.1.3.3 CAN Bus Termination
At each of the two extreme ends of the CAN bus backbone, a 120 Ω resistor is installed to terminate the
bus. In the G3X system, separate resistors are not required. Instead, termination resistors are provided
either within the LRUs themselves, or via termination adapters that plug into an LRU's CAN connection.
• The GEA 24, GSU 25, GAD 29, GPS 20A, and G5 installation kits provide a 9-pin termination
adapter that provides termination when attached to the device's main connector. The termination
adapter contains a 120 Ω resistor that is connected between pins 1 and 2
• The GDU 37X, GDU 4XX, GAD 27, and GSU 73 contain a 120 Ω resistor inside the unit that
provides termination when the CAN LO pin is connected externally to the CAN TERM pin
(Figure 2-12).
• The GSA 28 and GTR 20/200 contain a 120 Ω resistor inside the unit that provides termination
when the two CAN TERM pins are connected together
• The GMA 245 and GI 260 do not have provisions for CAN termination, and cannot be installed at
the end of the CAN bus. The total amount of extra wire length added to the CAN HI and CAN LO
wires on the GI 260 pigtail harness should not exceed 0.4 meters (15 inches).
190-01115-01
Rev. AA
Section 22.3). At minimum, the CAN bus shield should always be
SHIELD GROUNDED AT EACH SHIELD GROUNDED AT EACH
DAISY-CHAINED LRU, RECOMMENDED DAISY-CHAINED LRU, RECOMMENDED
SHIELD GROUNDED AT CAN BUS TERMINATIONS, REQUIRED SHIELD GROUNDED AT CAN BUS TERMINATIONS, REQUIRED
Figure 2-10 CAN Bus Shield Grounding
G3X/G3X Touch Installation Manual - Installation Preparation
DAISY-CHAINED DAISY-CHAINED
LRU ON CAN BUS LRU ON CAN BUS
PXXX JXXX PXXX JXXX
CAN-H CAN-H
CAN-L CAN-L
SHIELD GROUND SHIELD GROUND
CAN BUS TERMINATION CAN BUS TERMINATION
PXXX JXXX PXXX JXXX
CAN-H CAN-H
CAN-L CAN-L
SHIELD GROUND SHIELD GROUND
(Figure
(Figure 2-13 and Figure
2-11).
2-14).
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