The contrast of CAN bus line and RS485 bus line is analysed

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Introduction: In North America and Western Europe, agreement of CAN bus line has become car computer to control system and embedded the standard bus line of industrial control local area network, the J1939 agreement that and have is large freight car and design of car of heavy industry machine only for rock-bottom agreement with CAN. The definition CAN of CAN bus line and RS485 bus line is controller local area network subsidiary channels in the human body through which vital energy (Controller Area Network, CAN) abbreviation, by research and development and product of manufacturing car electron famous German BOSCH company was developed, make international standard finally (ISO11898) . It is one of spot bus line with the widest application on international. In North America and Western Europe, agreement of CAN bus line has become car computer to control system and embedded the standard bus line of industrial control local area network, the J1939 agreement that and have is large freight car and design of car of heavy industry machine only for rock-bottom agreement with CAN. In recent years, the high reliability that its have and good mistake detect ability is taken seriously, be controlled at car computer by wide application radiate of abominable, electromagnetism mixes system and environmental temperature by force the industrial environment with big vibration. Rs - 485 use means of job of half duplex operation, support occupies communication more. Rs - the bus line that develop of network of 485 bus line attacks to use terminal to match commonly structure. Use a bus line to string together each node namely receive rise, do not support annular or star network. Rs - 485 use the balance is sent and poor cent is received, because this is had,restrain in all the ability that the model disturbs. Add bus line to send and receive appliance to have tall sensitivity, can detect low the voltage to 200mv, reason transmission signal can be beyond kilometre get resumptive. Some Rs - 485 send and receive implement so that modification input impedance allows to will amount to the division check the number of 8 times above to join same bus line. Rs - 485 the commonnest application are to be below industrial environment but the communication between interior of controller of process designing logic. CAN bus line and application of RS485 bus line are summarized before, the means such as net of RS232 of much have the aid of of PC and intelligent equipment communication, RS485, aether, basically depend on the interface of equipment is normative. But the physical medium layer that RS232, RS485 can represent news report only and link layer, if want to realize the two-way visit of data, must oneself write communication application program, but the standard that majority of this kind of program cannot accord with ISO ／ OSI, can realize singler function only, apply to single facility type, the program does not have versatility. In the equipment network that becomes in RS232 or RS485 equipment couplet, if facility amount exceeds 2, must use RS485 to make communication medium, want between the equipment of RS485 net contact is passed only " advocate (Master) " ability of equipment change trains comes true, this advocate equipment is PC normally, and one allows to exist only in net of this kind of equipment advocate equipment, the others is entirely from (Slave) equipment. And technology of spot bus line is a foundation with model of ISO ／ OSI, have complete software to support a system, can solve bus line control, conflict to detect, link is safeguarded wait for a problem. Equipment of spot bus line becomes a network automatically, the derelict ／ cent from equipment or allow a lot of advocate exist. Be in same a product that manufacturer differs on administrative levels is OK crossing-over, each other is had to operate a gender between equipment. Present bus line format is very much, what characteristic does CAN photograph have to other bus line? Above all, compare great master familiar to the ear can the 485 bus line of detailed, 485 bus line are standard of a kind of n only, not be the agreement with new what, with 232 about the same, of course so saying is not very appropriate, but conduce to everybody understanding. CAN of bus line of PK RS485 of CAN bus line (Controller Area Network) the category that attributes spot bus line, it is a kind of active support distributed control or real time pilot are serial communication network. Than at present RS - the 485 distributed control systems that are based on R line compose to build, the distributed control system that is based on CAN bus line has clear advantage in the following respect: 1) CAN controller works at how advocate means, each node in the network can visit lien according to bus line (depend on message identifier) use nondestructive structure chase an arbitral means to compete to transmit data to bus line, and CAN agreement abolished station address codes, and acting code with undertaking to communication data, this can make different node receives same data at the same time, these characteristics make the data between each node connects the network that CAN bus line forms the sex when trustworthy is strong, and make redundant structure easily, increase the flexibility of systematic dependability and system. And use RS - 485 can make system of construction of type of principal and subordinate, communication means also can with advocate the means of station poll undertakes, real time sex of the system, dependability is poorer. 2) two output that CAN bus line passes 82C250 of chip of CAN controller interface carry CANH and CANL and physical bus line to be linked together, and the state that CANH carries can be tall n or suspension condition only, CANL end can be low n or suspension condition only. This can appear with respect to guarantee against resemble be in RS - in 485 networks, have a mistake when the system, appear when knaggy dot transmits data to bus line at the same time, bring about bus line to present short circuit, damage thereby the phenomenon of certain node. And CAN node is had below wrong and severe case shut output function automatically, in order to make the operation of other node on bus line insusceptible, assure to won't give a phenomenon to be in the network thereby, select occurrence issue because of specific item, make bus line is in " dead lock " condition. 3) CAN has perfect communication agreement, can come true by CAN controller chip and its interface chip, reduced development difficulty of the system greatly thereby, shortened development cycle, these are the RS that have electric agreement merely only - 485 can not be likened to. RS - 485 with CAN - the character of Bus is comparative CNC Milling