Electro-Voice System Controller NetMax N8000 - Manual (Page 36)

Appendix
36
NetMax N8000 System Controller
Owner’s manual
5.4 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 Topology of the CAN bus