Can-Bus Principles - Electro-Voice PWS-4 Owner's Manual

5 CAN-Bus Principles

The network topology used by the CAN bus is based on the so-called "bus or line topology", i.e. all
participants are connected via a single two-wire cable (Twisted-Pair cable, shielded or unshielded) with the
cabling running from one participant on the bus to the next, allowing unlimited communication among all
devices. In general, it does not matter if the bus member is a power amplifier, a N8000 or a UCC1 USB-
CAN converter. Thus, the N8000 can be connected at any place of the CAN bus. In total, up to 100 devices
can be connected to one CAN bus.
The CAN bus has to be terminated with a 120 Ω terminating resistor at both ends. If the termination is
missing or an improper resistor value is used, network errors can occur as a signal is reflected on the bus
at both bus ends. Because of the superposition of the reflection with the original signal, the original signal
is blurred. This may result in the loss of data. In order to prevent or minimize reflections at the bus ends,
terminators are used as they "absorb" the energy of the signal.
Since the CAN interfaces of all EVI Audio appliances are galvanically separated from the rest of the
circuitry, network cabling also carries a common ground conductor (CAN_GND) ensuring that all CAN-
interfaces in the network are connected to a common ground potential.
By using a CAN bus repeater a connection between two independent and self-contained CAN bus systems
can be created. Thus, the following can be achieved:
• Increase of the max. number of members
A maximum of 100 devices can be connected to one CAN bus. This number can be increased up to
250 by connecting several CAN bus systems. This limitation of exactly 250 devices results from the
addressing scheme used by the CAN bus. The addressing scheme allows the allocation of a maximum
of 250 different CAN device addresses.
• Improvement of signal quality
With CAN bus systems, whose bus length exceeds 1000 meters, a CAN bus repeater should be used.
The CAN bus repeater accomplishes a signal processing and a reinforcement of the bus signals. The
internal running time of the repeaters of approx. 150 ns corresponds to an extension of the bus over
approx. 45 meters.
• Creation of alternative network topologies
By using one or several repeaters, not only the above-mentioned bus topology, but the creation of
other network topologies are also possible.
Bus Topology of the CAN bus
PROGRAMMABLE WALL STATION
Owner's manual 19