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Appendix B Cabling Requirements
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National Instruments Corporation B-5 Getting Started with CAN for Windows NT
Cable Specifications
Cables should meet the physical medium requirements specified in
ISO 11898, shown in Table B-2.
Belden cable (3084A) meets all of those requirements, and should be
suitable for most applications.
Cable Lengths
The allowable cable length is affected by the characteristics of the cabling
and the desired bit transmission rates. Detailed cable length requirements
can be found in the ISO 11898, CiA DS 102, and DeviceNet specifications.
ISO 11898 specifies 40 m total cable length with a maximum stub length
of 0.3 m for a bit rate of 1 Mb/s. The ISO 11898 specification says that
significantly longer cable lengths may be allowed at lower bit rates, but
each node should be analyzed for signal integrity problems.
Table B-3 lists the DeviceNet cable length specifications.
Table B-2.
ISO 11898 Specifications for Characteristics of a CAN_H and
CAN_L Pair of Wires
Characteristic Val ue
Impedance 108 Ω minimum, 120 Ω nominal,
132 Ω maximum
Length-related resistance 70 mΩ/m nominal
Specific line delay 5 ns/m nominal
Table B-3.
DeviceNet Cable Length Specifications
Bit Rate Thick Cable Thin Cable
500 kb/s 100 m 100 m
250 kb/s 200 m 100 m
100 kb/s 500 m 100 m