Refer to the following figure for an example of where termination resistors should be placed in a system with more than two devices. If multiple devices are placed along the cable, only the devices on the ends of the cable should have termination resistors. However, this requirement does not mean that every device should have a termination resistor. If the transmission line is not terminated, each signal change on the line causes reflections that may cause communication failures.īecause communication flows both ways on the CAN bus, CAN requires that both ends of the cable be terminated. The pair of signal wires (CAN_H and CAN_L) constitutes a transmission line. If all of the devices on the network meet the DeviceNet specifications, 64 devices may be connected to the network. Higher numbers of devices may be connected if the electrical characteristics of the devices do not degrade signal quality below ISO 11898 signal level specifications. If all of the devices meet the requirements of ISO 11898, at least 30 devices may be connected to the bus. The maximum number of devices depends on the electrical characteristics of the devices on the network. The following table lists the DeviceNet cable length specifications. 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. 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. Detailed cable length recommendations can be found in the ISO 11898, CiA DS 102, and DeviceNet specifications. The allowable cable length is affected by the characteristics of the cabling and the desired bit transmission rates. ISO 11898 Specifications for Characteristics of a CAN_H and CAN_L Pair of Wires Cabling Requirements for High-Speed CANĬables should meet the physical medium requirements specified in ISO 11898, shown in the following table.īelden cable (3084A) meets all of those requirements, and should be suitable for most applications. Connecting the optional CAN shield may improve signal integrity in a noisy environment. Shield is an optional connection when using a shielded CAN cable. These signals should be connected using twisted-pair cable. PCMCIA-CAN Cable PCMCIA-CAN Cable Connector Pin DescriptionsĬAN_H and CAN_L are signal lines that carry the data on the CAN network. All of the signals on the 5-pin screw terminal are connected directly to the corresponding pins on the 9-pin D-SUB. The arrow points to pin 1 of the 5-pin screw terminal block. The following figure shows the end of a PCMCIA-CAN cable. PCMCIA-CAN cables have both a 9-pin male D-SUB and Combicon-style pluggable screw terminal connector for each port. All High-Speed Series 2 PCI, PXI, and USB hardware is powered internally, so it is not necessary to supply V+, unless you have configured the VBAT jumper for EXT. V+ supplies bus power to the CAN physical layer if external power is required. V- serves as the reference ground for CAN_H and CAN_L. Optional CAN power supply if bus power or external VBAT is requiredĬAN_H and CAN_L are signals lines that carry the data on the CAN network. Pinout for 9-Pin D-SUB Connector Pinout for 9-Pin D-SUB Connector The following figure shows the 9-pin D-SUB connector pinout. The 9-pin D-SUB connector follows the pinout recommended by CiA DS 102. PCI-CAN, PXI-8461, USB-8473, and USB-8473s hardware have a 9-pin male D-SUB (DB9) connector for each port. Previous page next page High-Speed CAN Pinout Cable High-Speed PCI, PXI, and USB Connector Pinout
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