Baldor MN1928 Can wiring, Maximum, Baud Rate Bus Length, Opto-isolation power requirements

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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:

HThe 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	JP1
points) with resistors of a nominal value of 120Ω. 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.

HAll cables and connectors should have a nominal impedance of 120Ω. Cables should have a length related resistance of 70mΩ/m and a

nominal line delay of 5ns/m. A range of suitable CAN cables are available from Baldor, with catalog numbers beginning CBL004-5... .

HThe maximum bus length depends on the bit-timing configuration (baud rate). The table opposite shows the approximate maximum bus length (worst-case), assuming 5ns/m propagation delay and a total effective device internal in-out delay of 210ns at 1Mbit/s, 300ns at 500 - 250Kbit/s, 450ns at 125Kbit/s and 1.5ms at 50 - 10Kbit/s.

(1)CAN baud rate not supported on Baldor CAN.

(2)For bus lengths greater than about 1000m, bridge or repeater devices may be needed.

CAN	Maximum
Baud Rate	Bus Length
1Mbit/s	25m
500Kbit/s	100m
250Kbit/s	250m
125Kbit/s	500m
100Kbit/s (1)	600m
50Kbit/s	1000m
20Kbit/s	2500m(2)
10Kbit/s	5000m(2)

HThe 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.

HThe 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 (<0.3m at 1Mbit/s).

HThe 0V 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.

4.6.2.1Opto-isolation power requirements

On the NextMove ES, the CAN channel is opto-isolated. A voltage in the range 12-24V must be applied to pin 5 of the CAN connector. From this supply, an internal voltage regulator provides the 5V at 100mA required for the isolated CAN circuit. CAN cables supplied by Baldor are ‘category 5’ and have a maximum current rating of 1A, 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 500Kbit/s owing to the propagation delay of the opto-isolators.

MN1928 Input / Output 4-21