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The characteristics and differences between CAN bus and RS485
Zhongling| 2024-05-07| Return
CAN bus features:

1. International standard industrial grade fieldbus, reliable transmission and high real-time performance;

2. Long transmission distance (up to 10km) and fast transmission rate (up to 1MHz bps);

3. A single bus can connect up to 110 nodes and can easily expand the number of nodes;

4. Multi master structure, equal status of each node, convenient for regional networking, and high bus utilization;

5. High real-time performance, non-destructive bus arbitration technology, high priority nodes without delay;

6. The erroneous CAN node will automatically shut down and cut off the connection with the bus, without affecting the communication of the bus;

7. The message is a short frame structure with hardware CRC verification, with a low probability of interference and extremely low data error rate;

8. Automatically detect whether the message is successfully sent, and can be automatically resent by hardware, with high transmission reliability;

9. Hardware message filtering function, only receiving necessary information, reducing CPU burden, and simplifying software development;

10. Communication media can be ordinary twisted pair cables, coaxial cables, or optical fibers, etc;

11. The CAN bus system has a simple structure and extremely high cost-effectiveness.

RS485 interface standard features:

1. The electrical characteristics of RS485: Logic "1" is represented by the voltage difference between two lines as (2-6) V; The logic "0" is represented by the voltage difference between two lines as - (2-6) V. The interface signal level is lower than RS-232-C, making it less likely to damage the chip of the interface circuit. Moreover, this level is compatible with TTL level, making it convenient to connect with TTL circuits.

2. The maximum data transmission rate of RS485 is 10Mbps

3. The RS485 interface adopts a combination of balanced drivers and differential receivers, which enhances the ability to resist common mode interference and has good resistance to noise interference.

4. The maximum transmission distance standard value of the RS485 interface is 4000 feet, which can actually reach 3000 meters. In addition, the RS-232-C interface only allows one transceiver to be connected on the bus, which is a single station capability. The RS-485 interface allows up to 128 transceivers to be connected on the bus. It has multi site capability, allowing users to easily establish device networks using a single RS-485 interface. But only one transmitter can send at any time on the RS-485 bus.

5. Due to its excellent resistance to noise interference, long transmission distance, and multi station capability, the RS485 interface has become the preferred serial interface.

6. Because a half duplex network composed of RS485 interfaces generally only requires two wires, RS485 interfaces are transmitted using shielded twisted pair cables.

The difference between CAN bus and RS485:

1. Speed and distance: Both CAN and RS485 transmit at a high speed of 1Mbit/S, with a distance of no more than 100M, which can be said to be similar on high speeds. However, at low speeds, CAN can reach a distance of up to 10km at a speed of 5Kbit/S, while 485 can only reach a speed of around 1219 meters at even lower speeds (without any relays). It can be seen that CAN has absolute advantages in long-distance transmission.

2. Bus utilization: RS485 is a single master-slave structure, which means that there can only be one host on a bus, and communication is initiated by it. It does not issue commands, and the nodes below cannot send them. They must respond immediately after receiving a response, and the host will only inquire to the next node. This is to prevent multiple nodes from sending data to the bus, which may cause data confusion. And CAN bus is a multi master-slave structure, with each node having a CAN controller. When multiple nodes send data, they automatically arbitrate based on the ID number they send. This can ensure that the bus data is not messy, and once one node sends it, the other node can detect that the bus is idle and send it immediately. This eliminates the need for host queries, improves bus utilization, and enhances speed. So in systems with high practicality requirements such as cars, CAN bus or other similar buses are used.

3. Error detection mechanism: RS485 only specifies the physical layer and does not have a data link layer, so it cannot recognize errors unless there are some physical errors such as short circuits. This can easily cause a node to break down and desperately send data to the bus (keep sending 1), resulting in the entire bus being paralyzed. So once a node in RS485 fails, the bus network will hang up. The CAN bus has a CAN controller that can detect any errors on the bus. If there are more than 128 errors, it will automatically lock. Protect the bus. If errors are detected by other nodes or by itself, an error frame will be sent to the bus to prompt other nodes, and this data is incorrect. Be careful, everyone. Once a node CPU program on the CAN bus runs away, its controller automatically locks and protects the bus. So in networks with high security requirements, CAN is very strong.

4. Price and training cost: The price of CAN devices is about twice that of 485. Therefore, 485 communication is very convenient from a software perspective. As long as you understand serial communication, you can program. CAN requires low-level engineers to understand the complex layers of CAN, and writing upper computer software also requires understanding of CAN protocols. It can be said that the training cost is relatively high.

5. The CAN bus is connected to the physical bus through the two output terminals CANH and CANL of the CAN controller interface chip 82C250, and the status of the CANH end can only be high or suspended, while the status of the CANL end can only be low or suspended. This ensures that in an RS-485 network, when there is an error in the system and multiple nodes simultaneously send data to the bus, it will cause a short circuit on the bus and damage certain nodes. Moreover, CAN nodes have an automatic output shutdown function in case of serious errors, so that the operation of other nodes on the bus is not affected, ensuring that the bus is not in a "deadlock" state due to problems with individual nodes in the network.

6. CAN has a comprehensive communication protocol that can be implemented by the CAN controller chip and its interface chip, greatly reducing the difficulty of system development and shortening the development cycle. These are incomparable to RS-485, which only has electrical protocols.


Shenzhen Zhongling Technology Co., Ltd. has been committed to the wheeled robot industry since its establishment in 2013, researching, developing, producing, and selling wheel hub servo motors and drivers with stable performance. Its high-performance servo wheel hub motor drivers ZLAC8015, ZLAC8015D, and ZLAC8030L use CAN/RS485 bus communication, supporting the CinA301 and CiA402 sub protocols of the CANopen protocol/modbus RTU protocol, and can mount up to 16 devices; Supporting work modes such as position control, speed control, and torque control, suitable for various occasions of robots, greatly promoting the development of the robotics industry.

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