National Instruments 321372C-01 用户手册

Appendix B

Cabling Requirements

Getting Started with CAN for Windows NT

B-4

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 National Instruments Corporation

Figure B-5 shows how to configure your jumpers for internal or external 
power supplies.

Figure B-5.  Power Source Jumpers

The CAN physical layer is still isolated regardless of the power source 
chosen.

The PCMCIA-CAN and PCMCIA-CAN/2 are available with two types of 
cable. The DeviceNet (bus powered) cable requires that the CAN physical 
layer be powered from the bus cable power.

The internal-powered cable supplies power to the CAN physical layer from 
the host computer. The V+ pin is not connected to any internal signals, but 
the corresponding pins on the 9-pin D-Sub and the 5 pin Combicon-style 
connectors are still connected. The V– pins serves as the reference ground 
for the isolated signals.

The CAN physical layer is isolated from the computer in both types of 
cable.

If the CAN physical layer is powered from a bus power supply, the power 
supply should be a DC power supply with an output of 10 V to 30 V. The 
power requirements for the CAN ports for Bus-Powered configurations are 
shown in Table B-1. You should take these requirements into account when 
determining requirements of the bus power supply for the system.

Table B-1.  Power Requirements for the CAN Physical Layer for 

Bus-Powered Versions

Voltage Requirement

V+ 10-30 VDC

Current Requirement

40 mA typical 
100 mA maximum

INT

EXT

a. Internal Power Mode

INT

EXT

b. External Power Mode

(Device Net)

1

2

3

1

2

3