Computer Accessories User Manual

Appendix C Cabling Requirements for PXI-8460 Low-Speed CAN
PXI-8461 or PXI-8460 and NI-CAN for Windows NT C-6 www.natinst.com
Philips also recommends an individual device RTH and RTL termination of
500 Ω to 16 kΩ. The PXI-8460 board ships with mounted RTH and RTL
values of 510 Ω ±5% per port. The PXI-8460 kit also includes a pair of
15 kΩ ±5% resistors for each port. After determining the termination of
your existing network or device, you can use the following formula to
indicate which value should be placed on your PXI-8460 board in order to
produce the proper overall RTH and RTL termination of 100 to 500 Ω upon
connection of the board:
*R
RTH overall
should be between 100 and 500 Ω
**R
RTH of low-speed CAN interface
= 510 Ω ±5% (mounted) or 15 kΩ ±5% (in kit)
†R
RTH
= R
RTL
As the formula indicates, the 510 Ω ±5% shipped on your board will work
with properly terminated networks having a total RTH and RTL
termination of 125 to 500 Ω, or individual devices having an RTH and RTL
termination of 500 Ω to 16 kΩ. For communication with a network having
an overall RTH and RTL termination of 100 to 125 Ω, you will need to
replace the 510 Ω resistors with the 15 kΩ resistors in the kit. Please refer
to the next section, Replacing the Termination Resistors.
R
RTH overall*
†
1
1
R
RTH of low-speed CAN interface**
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1
R
RTH of existing network or device
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