Mint NextMove PCI Installation Manual download pdf (Page 43)

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Input / Output 4-27MN1933

4.6.5 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 PCI-2 is at the end

of the network then ensure that the appropriate jumper on the breakout board is fitted. These

will connect an internal terminating resistor. For the CANopen bus, jumper J8 labelled ‘CO

Term’ must be fitted. For the Baldor CAN bus, jumper J7 labelled ‘BC Term’ must be fitted.

H All cables and connectors should have a nominal impedance of 120 Ω. Cables should have

a length related resistance of 70 mΩ/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 5ns/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 1000m,

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 PCI-2 or

CAN peripheral devices are within the common mode range of the receiver circuitry of

other nodes on the network.

4.6.5.1 Opto-isolation

On the NextMove PCI-2 breakout board, 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 VDC 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 PCI-2 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.

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)

1 2 ... 38 39 40 41 42 43 44 45 46 47 48 ... 125 126

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Mint NextMove PCI Installation Manual Page 43

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