Operation Manual

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Wiring | AP70/AP80 Installation Manual
Terminating the CAN bus
The CAN bus must have a terminator at each end of the backbone.
In a default autopilot system the CAN bus expands from the AC80A, AC80S or AC85 Autopilot
computer. This computer includes a terminator on the SI80 board, enabled by the micro
switch.
- Set the switch to ON when the SI80 board is at the end of the CAN bus
- Set the switch to OFF when the SI80 board is used as additional power supply to the CAN
bus
Factory default setting of SI80 terminator is OFF.
For location of the dip switch, refer to the illustrations inside the computer unit.
A terminator in the other end of the CAN bus can be of the following:
• An SI board (in SI80, AC80A, AC80S or AC85 computer) with enabled terminator
• A power cable with built in terminator (plug marked 120 ohm)
• A single terminator plug (marked 120 ohm)
Shield connection
It is required to use shielded cables to meet radio frequency interference requirements as
defined in the NMEA 2000 specification:
• The shield shall not be electrically connected within the interface to the electronic device
chassis or ground
• The shield shall be electrically continuous through the network connection
• The shield shall be connected to ground at a single point, normally the ship’s ground at the
source of network power
Power supply
¼ Note: Wheelmark/US Coast Guard approved systems require a Power Failure alarm. In such
installations the master station control unit and the autopilot computer with the SI80 board
for CAN bus supply must be connected to different independent power supplies.
¼ Note: It is recommended to install an external on/off switch for the Autopilot Computer
power supply.
¼ Note: Do not connect the power cable to the same terminals as the start batteries, drive
units, thruster or other high current products
¼ Note: If joining to an existing NMEA 2000 network or similar CAN bus network that has its
own power supply, use an NMEA 2000 Gateway to isolate the two power supplies.
Powering the CAN bus
In a default autopilot system the SI80 board (in the SI80, AC80A, AC80S or AC85 computer) is
used for powering the CAN bus backbone.
For larger systems additional power should be added at a central point in the backbone to
balance the voltage drop of the network. Additional power should be supplied by using an
SI80 board. Refer “Network LEN” on page 24.
ON OFF