www.baldormotion.com
4-22 Input / Output
MN1928
4.6.2 CAN wiring
A very low error bit rate over CAN can only be achieved with a suitable wiring scheme, so the
following points should be observed:
H
The two-wire data bus line may be routed parallel, twisted and/or shielded, depending on
EMC requirements. Baldor recommend a twisted pair cable with the shield/screen
connected to the connector backshell, in order to reduce RF emissions and provide
immunity to conducted interference.
H
The bus must be terminated at both ends only (not at intermediate
points) with resistors of a nominal value of 120
Ω
. This is to reduce
reflections of the electrical signals on the bus, which helps a node to
interpret the bus voltage levels correctly. If the NextMove ES is at the
end of the network then ensure that jumper JP1, located just behind
the status display, is in position. This will connect an internal
terminating resistor.
H
All cables and connectors should have a nominal impedance of
120
Ω
. Cables should have a length related resistance of 70 m
Ω
/m
and a nominal line delay of 5 ns/m. A range of suitable CAN cables are available from Baldor,
with catalog numbers beginning CBL004-5... .
H
The maximum bus length depends on the bit-timing
configuration (baud rate). The table opposite shows
the approximate maximum bus length (worst-case),
assuming 5 ns/m propagation delay and a total
effective device internal in-out delay of 210 ns at
1 Mbit/s, 300 ns at 500 - 250 Kbit/s, 450 ns at
125 Kbit/s and 1.5 ms at 50 - 10 Kbit/s.
(1)
CAN baud rate not supported on Baldor CAN.
(2)
For bus lengths greater than about 1000 m,
bridge or repeater devices may be needed.
H
The compromise between bus length and CAN baud rate must be determined for each
application. The CAN baud rate can be set using the
BUSBAUD
keyword. It is essential
that all nodes on the network are configured to run at the same baud rate.
H
The wiring topology of a CAN network should be as close as possible to a single line/bus
structure. However, stub lines are allowed provided they are kept to a minimum (<0.3 m at
1 Mbit/s).
H
The 0 V connection of all of the nodes on the network must be tied together through the
CAN cabling. This ensures that the CAN signal levels transmitted by NextMove ES or
CAN peripheral devices are within the common mode range of the receiver circuitry of
other nodes on the network.
4.6.2.1 Opto-isolation power requirements
On the NextMove ES, the CAN channel is opto-isolated. A voltage in the range 12-24 V must
be applied to pin 5 of the CAN connector. From this supply, an internal voltage regulator
provides the 5 V at 100 mA required for the isolated CAN circuit. CAN cables supplied by
Baldor are ‘category 5’ and have a maximum current rating of 1 A, so the maximum number of
NextMove ES units that may be used on one network is limited to ten. Practical operation of
the CAN channel is limited to 500 Kbit/s owing to the propagation delay of the opto-isolators.
JP1
CAN
Maximum
Baud Rate
Bus Length
1 Mbit/s
25 m
500 Kbit/s
100 m
250 Kbit/s
250 m
125 Kbit/s
500 m
100 Kbit/s
(1)
600 m
50 Kbit/s
1000 m
20 Kbit/s
2500 m
(2)
10 Kbit/s
5000 m
(2)
Servo Systems Co. • 115 Main Road • P.O. Box 97 • Montville, NJ,
07045-0097 • (973) 335-1007 • Toll Free: (800) 922-1103
Fax: (973) 335-1661 • www.servosystems.com
