AppendixC CablingRequirements for PXI-8461 High-Speed CAN
©NationalInstruments Corporation C-5 PXI-846xand NI-CAN for Windows NT
Cable Specifications
Cables should meet the physical medium requirements specified in
ISO 11898, shownin Table C-2.
Belden cable (3084A) meets all of those requirements and should be
suitable for most applications.
Cable Lengths
Theallowable cable length is affected by the characteristics of the cabling
andthe desired bit transmission rates. Detailed cable length requirements
can be found in ISO 11898, CiA Draft Standard 102, and the DeviceNet
Specification.
ISO 11898 specifies40 m total cable length w ith a maximum stub length
of0 .3 m fora bit rate of 1 Mb/s. The ISO 11898 specification sayst hat
significantlylonger cable lengths may be allowed at lower bit rates, but
each nodeshould be analyzed for signalintegrity problems.
TableC-3 lists the DeviceNet cable length specifications.
TableC-2. ISO 11898 Specifications for Characteristics of a CAN_H
andCAN_L Pair of Wires
Characteristic Valu e
Impedance 108Ωminimum, 120 Ωnominal,
132Ωmaxi mum
Length-related resistance 70mΩ/m nominal
Specificline delay 5 ns/m nominal
TableC-3. DeviceNet Cable Length Specifications
BaudR ate TrunkLength
DropLength
Maximum
DropLength
Cumulative
500 kb/s 100 m (328 ft) 6m(20ft) 39m (128 ft)
250 kb/s 250 m (820 ft) 6m(20ft) 78m (256 ft)
125 kb/s 500 m (1640 ft) 6m(20ft) 156m (512 ft)