Cabling Requirements For The Ni 9852; Cable Specifications; Determining The Necessary Termination Resistance For The Board; Number Of Can Nodes - National Instruments NI-9852 Getting Started

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Figure 2. Connecting Both Ports of the NI 9852 to CAN Buses

Cables should meet the physical medium requirements specified in ISO 11898,

shown in the following table. Belden cable (3084A) meets all these requirements

and should be suitable for most applications.

Characteristic

Length-related resistance

Length-related capacitance: CAN_L and ground, CAN_H and ground, CAN_L

and CAN_H

Table 3. ISO 11898 Specifications for Characteristics of a CAN_H and CAN_L Pair of Wires

Unlike High-Speed CAN, Low-Speed/Fault-Tolerant CAN requires termination at the

Low-Speed/Fault-Tolerant CAN transceiver instead of on the cable itself. Termination

requires two resistors, RTH for CAN_H and RTL for CAN_L. This configuration allows

the Philips Fault-Tolerant CAN transceiver to detect and recover from bus faults. It is

important to determine the overall termination of the existing network, or the

termination of the individual device, before connecting it to a Low-Speed/Fault-

Tolerant port. Philips recommends an overall RTH and RTL termination of 100 to

500 Ω (each) for a properly terminated low-speed network.

Termination on the low-speed/fault-tolerant ports of the NI 9852 is set through the

NI 985x software to either 1 kΩ or 5 kΩ.

The maximum number of nodes depends on the electrical characteristics of the

nodes on the network. If all of the nodes meet the requirements of Low-Speed/

Fault-Tolerant CAN, up to 32 nodes may be connected to the bus.

NI-9852 Getting Started

Value

90 mΩ/m nominal

30 pF/m nominal

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