Cables, CAN H and CAN L

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: CAN H And CAN L Distributing Signals Within Multiplex Communication Network

Courtesy of VOLVO CARS OF NORTH AMERICA.

The wires CAN H and CAN L must not be confused with HS CAN and LS CAN, which indicate the speed of the CAN network. CAN H and CAN L are the names for the wires used to distribute the signals in the multiplex communications network.

Communication takes place using two wires. These two wires are twisted together and are made of a copper material.

The voltage levels for communication take place using differential voltage levels. Two twisted-pair wires and differential voltage levels are used because this makes the network less susceptible to interference.

The same message is transferred simultaneously by both cables, but different voltage levels are used.

Binary 1 = 2.5 V on both CAN H and CAN L.
Binary 0 = 4 V on CAN H and 1 V on CAN L.

When measured between CAN L and earth, the average voltage level is approx. 2.3 V.

When measuring between CAN H and ground, the average voltage level is approx. 2.8 V. When measuring between the two CAN wires, with normal traffic on the network, the average voltage level is approx. 0.55-0.90 V (up to max. 0.6-1.4 V).

Volvo's CAN-net meets ISO 11898-2. Other standard is 11898-3 where the voltage on CAN H changes from approx. 5 V to approx. 1 V, and CAN L from approx. 0 V to approx. 4 V when changing from logic "0" to logic "1". Other standard is SAE J2411 where only one cable is used for CAN-communication.