Appendix B Cabling Requirements for PXI-8461 High-Speed CAN
© National Instruments Corporation B-5 PXI-8461 or PXI-8460 and NI-CAN for Windows NT
Cable Specifications
Cables should meet the physical medium requirements specified in
ISO 11898, shown in TableB-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 ISO 11898, CiA Draft Standard 102, and the DeviceNet
Specification.
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.
TableB-3 lists the DeviceNet cable length specifications.
Table B-2. ISO 11898 Specifications for Characteristics of a CAN_H and
CAN_LPair of Wires
Characteristic Valu e
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
Baud Rate Trunk Length Drop Length
Maximum Drop Length
Cumulative
500 kb/s 100 m (328 ft) 6 m (20 ft) 39 m (128 ft)
250 kb/s 250 m (820 ft) 6 m (20 ft) 78 m (256 ft)
125 kb/s 500 m (1640 ft) 6m (2 0ft) 156 m (512 ft)