Appendix G - Can Bus Connection - Starcom Systems Helios User's Manual Manual

Helios Users Guide
Appendix G – CAN Bus Connection
Controller Area Network (CAN) bus is a multiplexed wiring system used to
connect intelligent devices such as Electronic Control Units (ECU's) onto
vehicles, allowing data to be transferred in a low-cost and reliable manner.
CAN bus uses two dedicated wires for communication. The wires are called
CAN High and CAN Low. When the CAN bus is in idle mode, both lines carry
2.5 V. When data bits are being transmitted, the CAN high line goes to 3.75 V
and the CAN low drops to 1.25 V, thereby generating a 2.5 V differential
between the lines.
To identify the actual CAN bus wires look for a twisted pair of thin wires. They
can be found all over the vehicle, sometimes in with a conventional main loom.
In most vehicles, the CAN wires are placed in the diagnostic plug on the
driver's side, usually from below.
While the vehicle is stationary and the ignition is on, the CAN wires run a
speed pulse signal. You can use a LED device, which measures pulses above
1.5-2 V, to identify the CAN wires. The high speed pulses will signify the CAN
High wire, the low speed pulses – the CAN Low wire.
Installation
Connect the CAN High wire to CAN High BLACK/GRAY cable on 24-pin Helios
wire harness (Pin 12).
Connect the CAN Low wire to CAN Low GRAY/BLUE cable on 24-pin Helios
wire harness (Pin 24).
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