CN111181828B - Device for realizing CAN bus communication star connection - Google Patents
Device for realizing CAN bus communication star connection Download PDFInfo
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- CN111181828B CN111181828B CN202010106334.2A CN202010106334A CN111181828B CN 111181828 B CN111181828 B CN 111181828B CN 202010106334 A CN202010106334 A CN 202010106334A CN 111181828 B CN111181828 B CN 111181828B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/40—Bus networks
- H04L12/40006—Architecture of a communication node
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/44—Star or tree networks
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/40—Bus networks
- H04L2012/40208—Bus networks characterized by the use of a particular bus standard
- H04L2012/40215—Controller Area Network CAN
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Abstract
The invention provides a device for realizing CAN bus communication star connection, which comprises a logic processing unit and at least two CAN nodes, wherein the CAN nodes are respectively connected with the logic processing unit, and the logic processing unit is used for carrying out logic processing on received signals on a bus to realize the star connection function. The network layout of the traditional CAN bus CAN be simplified, the wiring cost and the wiring difficulty CAN be reduced, and stable communication CAN be realized during the multi-node complex network layout of the CAN bus.
Description
Technical Field
The invention relates to the technical field of CAN communication, in particular to a device for realizing CAN bus communication star connection.
Background
The CAN bus belongs to the field bus category, CAN carry out network connection on various intelligent machines, carries out unified control, has safe, effective and timely control functions, CAN provide functions of unified control or multi-master control and the like of a plurality of ports, and is widely applied to the fields of automobiles, aviation, navigation, factory automation, industrial mechanical control, medical appliances and the like at present. However, with the continuous expansion of the application range of the CAN bus, the traditional wiring form of the CAN bus gradually highlights its own defects, the wiring of a complex system is not only high in cost, but also very difficult, if the number of nodes is large, the bus cable becomes long, the transmission of bus signals is affected, and when the CAN nodes are combined into a star network, the length of each branch line cannot be too long.
In addition, the CAN node realized by the ARM soft core is very common in the CAN network, at present, the CAN node equipment realized by the ARM soft core needs to convert signals into CAN H and CAN L through a conversion chip when needing to access a CAN bus, if the CAN node realized by the ARM soft core CAN be directly accessed into the CAN network, the cost CAN be saved, the energy consumption CAN be reduced, and the communication stability CAN be improved due to one-stage less connection conversion.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects of the prior art, the invention provides a device for realizing CAN bus communication star connection, which CAN realize the star connection function by carrying out logic processing on received signals on a bus, simplify the network layout of the traditional CAN bus, reduce the wiring cost and the wiring difficulty, and realize stable communication when the CAN bus is provided with multiple nodes and complicated network layout.
The technical scheme is as follows: in order to achieve the technical effects, the technical scheme provided by the invention is as follows:
a device for realizing CAN bus communication star connection comprises a logic processing unit and at least two CAN nodes, wherein the types of the CAN nodes comprise a common CAN node and a soft core ARM node; the soft core ARM node is directly connected with the logic processing unit; the CAN node is connected with the logic processing unit through a CAN transceiver, wherein CAN _ H and CAN _ L cables of the common CAN node are respectively connected with CAN _ H and CAN _ L pins of the CAN transceiver, and the CAN transceiver is connected with the logic processing unit through RX and TX pins;
the logic processing unit controls communication among all nodes through a state machine, after the operation is started, the state machine always sends a recessive bit 1 to all nodes, all nodes judge that a bus enters an idle state when receiving continuous 11 recessive bits 1, at the moment, if a node needing to occupy the bus sends data to the logic processing unit, if only one CAN node A sends data, the CAN node A occupies the bus, and if a plurality of CAN nodes send data at the same time, the logic processing unit enters an arbitration stage;
in the arbitration phase, the logic processing unit processes signals of each CAN node as follows:
if the CAN node A is a common CAN node, the logic processing unit takes (RXA | (-TXA _ delay)) as an action signal of the CAN node A acting on other CAN nodes; where RXA is an actual output signal of CAN node a, | represents an or operation in a logical operation, — represents an inverted symbol, TXA represents a signal received by CAN node a, TXA _ delay represents a delay of time duration, which is performed on signal TXA, and delay ═ delay*+f×L，delay*The maximum propagation delay of the CAN transceiver is represented, f multiplied by L represents wiring delay, f is a delay parameter, and L is the wiring length between the CAN node and the CAN transceiver;
if the CAN node A is a soft core ARM node, the logic processing unit takes the RXA as an action signal of the CAN node A to act on other CAN nodes;
the signal finally sent to a CAN node B by the logic processing unit is the logical AND of the action signals acted on the node B by other nodes; according to an arbitration principle specified by a CAN protocol, each CAN node finally wins in arbitration to obtain a bus control right; (ii) a
After the arbitration phase is finished, the bus is occupied by a certain CAN node, and after the occupation is finished, the bus returns to an idle state to wait for the start of the next communication.
Further, the maximum delay time delay does not exceed 20% of the bit length.
Further, each CAN node interface of the logic processing unit has a data input terminal RX and a data output terminal TX; each data input terminal RX is connected to a pull-up resistor.
Further, 120 ohm impedance matching is adopted between CAN _ H and CAN _ L of the CAN transceiver.
Has the advantages that: compared with the prior art, the invention has the following advantages:
1. the logic processing unit is used for carrying out logic processing on signals among the connected CAN nodes, so that the bus function is realized through the logic processing unit, the star connection of each CAN node is realized, and bus wiring is not needed;
2. the device for realizing CAN bus communication star connection has flexible access CAN node equipment form, uses corresponding logic codes and reserves different node interfaces, and CAN access the node equipment with interfaces of CAN _ H and CAN _ L and CAN access the CAN equipment realized by ARM soft core.
3. When the CAN node realized by the ARM soft core is accessed, the node signal does not need to be converted into CAN _ H and CAN _ L signals through a conversion chip, so that the cost CAN be saved, the energy consumption CAN be reduced, and the communication stability CAN be improved.
4. The method for forming the star network is simple and reliable, the impedance matching of the branch nodes with unequal lengths is simple, calculation is not needed, and the impedance matching fixed rule is 120 ohms.
5. The invention has flexible wiring mode of forming a star network and greatly reduces the limitation on the length of the connecting line from each node to the logic processing unit.
6. The invention CAN simplify the network layout of the traditional CAN bus, reduce the wiring cost and the wiring difficulty, and realize the stable communication of the CAN bus during multi-node complex network layout;
7. when the invention forms a star network, no concentrator is needed to be added for network topology division.
Drawings
Fig. 1 is a diagram illustrating an exemplary structure of a device for implementing a CAN bus communication star connection according to the present invention.
Detailed Description
The invention will be further described with reference to the accompanying drawings and specific embodiments. It is to be understood that the present invention may be embodied in various forms, and that there is no intention to limit the invention to the specific embodiments illustrated, but on the contrary, the intention is to cover some exemplary and non-limiting embodiments shown in the attached drawings and described below.
Fig. 1 shows an example of an apparatus for implementing CAN bus communication star connection according to the present invention, including: the system comprises a logic processing unit, a node 1, a node 2 and a node 3, wherein the node 1, the node 2 and the node 3 are connected to the logic processing unit, and a reserved node interface is reserved in the logic processing unit; in the nodes 1, 2 and 3, the node 3 is a CAN node realized by an ARM soft core, namely a soft core ARM node, the nodes 1 and 2 are common nodes, namely nodes accessed to a logic processing unit through a CAN transceiver, the three nodes form a star network topology structure, the logic processing unit performs corresponding logic judgment and processing on the communication signal access of each node to realize bus communication among the CAN nodes, and when one of the three nodes has a fault, the other two nodes communicate normally. When the reserved node is not accessed, the communication of other three nodes is not influenced, and when the reserved node is accessed, the four nodes can normally communicate.
The device for realizing CAN bus communication star connection shown in FIG. 1 works according to the following principle:
the logic processing unit controls communication among all nodes through a state machine, after the operation is started, the state machine always sends a hidden bit 1 to all nodes, each node judges that a bus enters an idle state when receiving continuous 11 hidden bits 1, at the moment, if a node needing to occupy a CAN bus sends data to the logic processing unit, and if only one node sends data, the bus is directly occupied by the CAN node; if a plurality of CAN nodes send data simultaneously, the logic processing unit enters an arbitration phase.
In the arbitration phase, the logic processing unit mainly ensures that the CAN node with the highest priority occupies the bus, and normally, the confirmation of the bus for the node priority is judged according to the arbitration frame (namely, the ID field of the CAN node) of the node: for example, CAN node a and CAN node B, whose ID segments are both dominant 0 in the first bit, now assuming that node a has a higher priority than node B, the first bits of the a and B arbitration frames (i.e., data output to the bus) are the same, and priority is to be dropped at the next level, since a has a higher priority, the next level of a must be dominant 0 and the next level of B must be recessive 1. Node A and node B arbitrate according to the arbitration principle specified by the CAN protocol, and the arbitration result is that B fails in arbitration and A occupies the bus.
However, since the normal CAN node is connected to the logic processing unit through the CAN transceiver, the output of the CAN transceiver is affected by the output signal of the connected normal CAN node and also by the level received by the CAN transceiver from the logic processing unit. The effect is formed by: there will be a delay inside the CAN transceiver, and the time of this delay is denoted as delay*，delay*From the time when the signal of the logic processing unit enters the input terminal of the CAN transceiver to the time when the signal acts on the CANH terminal and the CANL terminal of the CAN transceiver, that is, the signal of the logic processing unit received by the CAN transceiver, to the time when the signal reaches the CANH terminal and the CANL terminal of the CAN transceiver and affects the output of the CAN transceiver, there is a delay between the signal and the CANH terminal*. And the data output by the CAN nodes connected with the CANH end and the CANL end of the CAN transceiver immediately act on the CANH end and the CANL end of the CAN transceiver. Based on the effect of this delay, the output data of the CAN transceiver would be such that: transfusion systemThe output signal is determined by the current signal of the CAN node and the signal input to the CAN transceiver by the logic processing unit, and in delay*Before time and at delay*After the time, the signal output by the logic processing unit has a jump effect on the CANH end and CANL end of the CAN transceiver, so that the final output data of the CAN transceiver is in delay*Before and after the jump occurs, the jump is not processed and directly acts on other nodes to influence the arbitration result of the bus.
To eliminate this jump, the present invention uses a signal opposite to the jump signal to superimpose the signal output from the CAN transceiver, thereby eliminating the jump.
Based on the above analysis, the present invention performs bus arbitration using the following method:
if the CAN node A is a common CAN node, the logic processing unit takes (RXA | (-TXA _ delay)) as an action signal of the CAN node A acting on other CAN nodes; where RXA is an actual output signal of CAN node a, | represents an or operation in a logical operation, — represents an inverted symbol, TXA represents a signal received by CAN node a, TXA _ delay represents a delay of time duration, which is performed on signal TXA, and delay ═ delay*+f×L，delay*The maximum propagation delay of the CAN transceiver is represented, f multiplied by L represents the wiring delay, f is a delay parameter, and L is the wiring length between the CAN node and the CAN transceiver.
delay*The maximum cyclic delay determination may be selected according to the selected CAN transceiver manual, and f × L represents the wiring delay. Taking the CAN transceiver TJA1051 as an example, as CAN be seen from the data manual, the maximum propagation delay is 220ns, and the minimum propagation delay is 40ns, so 220ns is taken as delay*Time. Considering the wiring length again, if the CAN transceiver and the logic processing unit are on the same circuit board, the wiring is very short, and in this case, only delay is needed*The time is slightly enlarged, the enlarged time is wiring delay and is in direct proportion to the wiring length, and the calculation formula is f multiplied by L. When the CAN transceiver and the logic processing unit are not on the same circuit board, the wiring delay increases with the increase of the length of the cable from the CAN transceiver to the logic processing unitThe maximum delay time is not more than 20% of the bit length, the maximum delay time is the sum of the inherent delay and the wiring delay of the CAN transceiver, and the bit length is related to the selected baud rate, for example, the selected baud rate is 500K, the length of the bit is 1S/500K, and the length of the bit is 2 us.
In this embodiment, in the star network topology shown in fig. 1, impedance matching of each node branch with different lengths is simple, and an impedance matching fixed rule of 120 ohms is used, that is, 120 ohms impedance matching is adopted between CAN _ H and CAN _ L of a CAN transceiver. The CAN node interface CAN be reserved on the logic processing unit CPLD circuit board, and the interface form CAN be designed according to the requirements, so that the expansion is very convenient.
In one or more embodiments of the device for implementing CAN bus communication star connection according to the present invention, each CAN node interface of the logic processing unit has a data input RX and a data output TX; each data input end RX is connected with a pull-up resistor in series, when a CAN node is not connected or fails, because the pull-up resistor exists, a recessive level 1 is sent, and the logic operation results of other signals are not influenced.
It is to be understood that the features listed above for the different embodiments may be combined with each other to form further embodiments within the scope of the invention, where technically feasible. Furthermore, the particular examples and embodiments of the invention described are non-limiting, and various modifications may be made in the structure, steps, and sequence set forth above without departing from the scope of the invention.
The above-described embodiments, particularly any "preferred" embodiments, are possible examples of implementations, and are presented merely for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the technology described herein, and such variations and modifications are to be considered within the scope of the invention.
Claims (4)
1. A device for realizing CAN bus communication star connection is characterized by comprising a logic processing unit and at least two CAN nodes, wherein the types of the CAN nodes comprise a common CAN node and a soft core ARM node; the soft core ARM node is directly connected with the logic processing unit; the CAN node is connected with the logic processing unit through a CAN transceiver, wherein CAN _ H and CAN _ L cables of the common CAN node are respectively connected with CAN _ H and CAN _ L pins of the CAN transceiver, and the CAN transceiver is connected with the logic processing unit through RX and TX pins;
the logic processing unit controls communication among all nodes through a state machine, after the operation is started, the state machine always sends recessive bit 1 to all nodes, all nodes judge that a bus enters an idle state when receiving continuous 11 recessive bit 1, at the moment, if a node needing to occupy the bus sends data to the logic processing unit, if only one CAN node A sends data, the CAN node A occupies the bus, and if a plurality of CAN nodes send data at the same time, the logic processing unit enters an arbitration stage;
in the arbitration phase, the logic processing unit processes signals of each CAN node as follows:
if the CAN node A is a common CAN node, the logic processing unit takes (RXA | (-TXA _ delay)) as an action signal of the CAN node A acting on other CAN nodes; where RXA is an actual output signal of CAN node a, | represents an or operation in a logical operation, — represents an inverted symbol, TXA represents a signal received by CAN node a, TXA _ delay represents a delay of time duration, which is performed on signal TXA, and delay ═ delay*+f×L，delay*The maximum propagation delay of the CAN transceiver is represented, f multiplied by L represents wiring delay, f is a delay parameter, and L is the wiring length between the CAN node and the CAN transceiver;
if the CAN node A is a soft core ARM node, the logic processing unit takes the RXA as an action signal of the CAN node A to act on other CAN nodes;
the signal finally sent to a CAN node B by the logic processing unit is the logical AND of the action signals acted on the node B by other nodes; according to an arbitration principle specified by a CAN protocol, each CAN node finally wins in arbitration to obtain a bus control right;
after the arbitration phase is finished, the bus is occupied by a certain CAN node, and after the occupation is finished, the bus returns to an idle state to wait for the start of the next communication.
2. The apparatus of claim 1, wherein the maximum delay time delay is not more than 20% of the bit length.
3. The apparatus of claim 1, wherein each CAN node interface of the logic processing unit has a data input RX and a data output TX; each data input terminal RX is connected to a pull-up resistor.
4. The device of claim 3 wherein the CAN transceiver is configured to use 120 ohm impedance matching between CAN _ H and CAN _ L.
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