The Network Construction

The network construction

General
The network is made up of a number of control modules (sometimes called nodes)which are connected to each other serially via two communication cables. Each control module is supplied with power and grounded individually and receives messages /commands via the two communication cables. In both networks (high and low speed sides) the control modules are serially connected. In the event of an open-circuit those control modules beyond the open-circuit will not be able to communicate with other parts of the network.

High and low speed sides on the network
The network consists of two parts. A high speed side which transfers (HS CAN) signals/messages between the central electronic module and the control modules in the engine compartment, and a low speed side (LS CAN) which transfers the signals /messages between the central electronic module and the control modules in the passenger compartment.
The interface between the high and low speed sides is supplied by the central electronic module which speeds up or slows down the communication between the two network sides.

Transfer speeds
The Volvo Controller area network (CAN) has two transfer speeds.
- HS CAN (High speed) has a transfer speed of 250 Kbps
- LS CAN (Low speed) has a transfer speed of 125 Kbps.
1 Kbps = 1024 bit per second (1byte = 8 bits).
For serial communication (Volcano Lite) between a control module and a slave control module the transfer speed is 10.4 Kbps.

Terminating resistor
To prevent electrical reflections and interference in the Controller area network (CAN) there are terminating resistors which bridge CAN H and CAN L. One in each end point on both the high and low speed side of the network. Each terminating resistor has a resistance of 120 ohm.
- The terminating resistor for the high speed Controller area network (CAN) is positioned in the brake control module/ABS control module and in the engine control module (ECM) or electronic throttle module. The terminating resistor is in the engine control module, on models without an electronic throttle module
- There are terminating resistors for the low speed Controller area network (CAN) in the upper electronic module and the rear electronic module.
Both the terminating resistors create a parallel circuit The following resistors can be measured under specified conditions:
- When the Controller area network (CAN) is intact the resistance in the network is approximately 60 ohm
- In the event of an open-circuit in the wiring, the resistance in the network is approximately 120 ohm
- In the event of a short-circuit between the communication cables the resistance is approximately 0 ohm.