System Connection; Can-Bus Connection; Bus Terminal Resistance - ZLG USBCAN-4E-U User Manual

Guangzhou ZHIYUAN Electronics Co., Ltd.
 When data transmission by the CAN controller is successful, the CAN indicator
becomes green. When the transmission is error or the CAN controller has fault,
the CAN indicator becomes red.

2.5 System Connection

2.5.1 CAN-bus Connection

When the USBCAN-4E-U interface card is connected to CAN-bus Bus, users only
need to connect CAN_L with CAN_L signal, CAN_H with CAN_H signal.
The CAN-bus network uses linear topology, and the two terminals of bus should be
connected with a 120Ω terminal resistance; if the number of nodes is greater than 2,
the intermediate node does not need to connect with a 120Ω terminal resistance. For
branch connections, the connection distance should not exceed 3m. The CAN-bus
connection is shown in Figure 2- 2.
Notes: The CAN-bus can use common twisted pair or shielded twisted pair. If the
communication distance exceeds 1Km, the section area of cable should be greater than
which depends on the specific distance. Generally, the longer the communication distance is, the
greater the section area of cable is.

2.5.2 Bus Terminal Resistance

In general, the two terminals of CAN-bus network should be added a terminal
matching resistance to improve communication reliability. The value of terminal
matching resistance is determined by the characteristic impedance of transmission
cable. For example, if the characteristic impedance of twisted pair is 120Ω, two
terminals of CAN-bus should be connected with a 120Ω terminal resistance. In
addition, the USBCAN-4E-U interface card uses CTM8251KAT and CTM8251KT
transceiver; therefore, if the other nodes on the network use different transceivers,
the terminal resistance must be calculated separately.
The terminal resistance (120Ω) is not connected between the internal CANH and
CANL. If the user needs to connect the terminal resistance at the node of the
interface card, it is necessary to connect the 120Ω terminal resistance to the terminal
R+ and R-, as shown in Figure 2- 2.
User Manual
Date: 2017/03/09
Industrial high performance CAN interface card
Figure 2- 2: CAN-bus network topology
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USBCAN-4E-U User Manual
©2017 Guangzhou ZHIYUAN Electronics
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