Compare can bus and RS485 bus

2022-08-02
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Comparison: can bus and RS485 bus

Abstract: in the past, the communication between PC and intelligent devices mostly relied on RS232, RS485, Ethernet and other methods, which mainly depended on the interface specification of the device. However, RS232 and RS485 can only represent the physical media layer and link layer of communication. If you want to realize two-way access to data, you must write your own communication application program...

can is the abbreviation of controller area network (can), which was developed by Bosch Company in Germany, which is famous for developing and producing automotive electronic products, and finally became an international standard (iso11898). It is one of the most widely used Fieldbus in the world. In North America and Western Europe, can bus protocol has become the standard bus for automotive computer control system and embedded industrial control area, and has J1939 protocol specially designed for large trucks and heavy machinery vehicles with can as the underlying protocol. In recent years, its high reliability and good error detection ability have been paid attention to. It has been widely used in automotive computer control systems and industrial environments with harsh ambient temperature, strong electromagnetic radiation and large vibration

rs-485 adopts half duplex working mode and supports multi-point data communication. RS-485 bus network topology generally adopts the bus type structure with terminal matching. That is, a bus is used to connect all nodes in series, and ring or star networks are not supported. RS-485 adopts balanced transmission and differential reception, so it has the ability to suppress common mode interference. In addition, the bus transceiver has high sensitivity and can detect the voltage as low as 200mV, so the transmission signal can be recovered from km away. Some RS-485 transceivers modify the input impedance to allow up to 8 times more nodes to be connected to the same bus. The most common application of RS-485 is the communication between programmable logic controllers in industrial environment

can bus and RS485 bus application overview

in the past, the communication between PC and intelligent devices mostly relied on RS232, RS485, Ethernet and other methods, which mainly depended on the interface specification of the device. However, RS232 and RS485 can only represent the physical media layer and link layer of communication. If you want to achieve two-way access to data, you must write your own communication application program. However, most of these programs can not meet the iso/osi specification, and can only achieve a single function. They are applicable to a single device type, and the program is not universal

among the RS232 or RS485 devices, if the number of devices exceeds 2, RS485 must be used as the communication medium. To exchange information between RS485 devices, it can only be achieved through the transfer of "master" devices. This master device is usually a PC. in this device, only one master device is allowed, and the rest are slave devices. The fieldbus technology is based on iso/osi model and has a complete software support system, which can solve the problems of bus control, conflict detection, link maintenance and so on. The fieldbus device is automatically formed without master/slave devices or multiple masters are allowed. At the same level, the products of different manufacturers can be interchanged, and the equipment has interoperability

there are many bus formats. What are the characteristics of can compared with other buses? First of all, let's compare the familiar 485 bus. 485 bus is only a level standard, not a new protocol. It's similar to 232. Of course, that's not very appropriate, but it helps you understand

can bus PK RS485 bus

can (controller area netwo's capacity reduction policy from central to local is being issued in succession) belongs to the field bus category. It is a serial communication network that effectively supports distributed control or real-time control. Compared with the current RS-485 distributed control system based on R line, the distributed control system based on CAN bus has obvious advantages in the following aspects:

1) the CAN controller works in the multi master mode, and each node in the network can compete to send data to the bus in the bit by bit arbitration mode without water loss structure according to the bus access priority (depending on the message identifier), Moreover, the CAN protocol abolishes the station address coding and instead encodes the communication data, which can make different nodes receive the same data at the same time. These characteristics make the data communication between nodes of the network composed of CAN bus more real-time, and easy to form a redundant structure, so as to improve the reliability and flexibility of the system. RS-485 can only form a master-slave structure system, and the communication mode can only be carried out in the way of master station polling. The real-time performance and reliability of the system are poor

2) the CAN bus is connected to the physical bus through the two output terminals canh and canl of the CAN controller interface chip 82C250. The status of the canh terminal can only be high-level or suspended, and the canl terminal can only be low-level or suspended. This will ensure that there will not be a short circuit in the bus and damage to some nodes when the system has errors and multiple nodes simultaneously send the sales price data to the bus as a detection instrument, which can not be viewed only. In addition, the CAN node has safety protection functions such as upper and lower limits and overload in case of serious errors, and has the function of automatically closing the output, so that the operation of other nodes on the bus will not be affected, so as to ensure that there will be no image in the network. Due to the problems of individual nodes, the bus is in a "deadlock" state

3) can has perfect communication protocol, which can be realized by CAN controller chip and its interface chip, which greatly reduces the difficulty of system development and shortens the development cycle, which is unmatched by RS-485 with only electrical protocol

rs-485 and can bus characteristics comparison

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