Appendix C
Cabling Requirements for PXI-8461 High-Speed CAN
©
National Instruments Corporation
C-5
PXI-846x and NI-CAN for Windows 98/95
Cable Specifications
Cables should meet the physical medium requirements specified in
ISO 11898, shown in Table C-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.
Table C-3 lists the DeviceNet cable length specifications.
Table C-2.
ISO 11898 Specifications for Characteristics of a CAN_H and
CAN_L Pair of Wires
Characteristic
Value
Impedance
108
Ω
minimum, 120
Ω
nominal,
132
Ω
maximum
Length-related resistance
70 m
Ω
/m nominal
Specific line delay
5 ns/m nominal
Table C-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)
6 m (20 ft)
156 m (512 ft)
