CN117478495A - Automatic configuration method and circuit for CAN communication terminal resistor - Google Patents
Automatic configuration method and circuit for CAN communication terminal resistor Download PDFInfo
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- CN117478495A CN117478495A CN202311366679.1A CN202311366679A CN117478495A CN 117478495 A CN117478495 A CN 117478495A CN 202311366679 A CN202311366679 A CN 202311366679A CN 117478495 A CN117478495 A CN 117478495A
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- 230000007175 bidirectional communication Effects 0.000 claims description 3
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L41/00—Arrangements for maintenance, administration or management of data switching networks, e.g. of packet switching networks
- H04L41/08—Configuration management of networks or network elements
- H04L41/0876—Aspects of the degree of configuration automation
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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
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L41/00—Arrangements for maintenance, administration or management of data switching networks, e.g. of packet switching networks
- H04L41/08—Configuration management of networks or network elements
- H04L41/0876—Aspects of the degree of configuration automation
- H04L41/0886—Fully automatic configuration
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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 discloses an automatic configuration method of CAN communication terminal resistance and a circuit thereof, which are used for calculating the impedance Rw of a CAN communication cable and matching an equivalent terminal resistance based on the impedance Rw of the CAN communication cable, wherein the equivalent terminal resistance=the impedance Rw of the CAN communication cable or the equivalent terminal resistance is approximately equal to the impedance Rw of the CAN communication cable; the invention effectively solves the engineering practical problem caused by mismatching of the terminal resistor and the cable impedance in the CAN communication field, and improves the reliability and stability of CAN communication.
Description
Technical Field
The invention belongs to the technical field of CAN communication, and particularly relates to an automatic configuration method and circuit of a CAN communication terminal resistor.
Background
CAN (Controller Area Network) bus communication is a two-wire serial communication network with high reliability, strong real-time performance and long transmission distance, has strong error detection capability, and is widely used in the fields of automobile central control systems, ship control systems and the like. CAN use a variety of physical mediums such as twisted pair, coaxial cable, fiber optic, etc. The most common is twisted pair, the signals are transmitted by using differential voltage, two signal lines are called CAN_H and CAN_L, the differential level between the two lines is about 0 when in static state, and the state is expressed as logic 1 and is called recessive; a logic 0 is represented by can_h being higher than can_l, referred to as dominant.
In general, when the load side impedance does not match the transmission line impedance, i.e. when R, based on transmission line theory L ≠Z 0 At this point, a portion of the signal will reflect back along the transmission line at the load end (point B) to the source end (point a). The magnitude of the reflection can be determined by the load reflection coefficient ρ L The reflection coefficient is defined as the ratio of the reflected voltage at the reflection node to the incident voltage, as shown in the following equation:
in which R is L Is the load impedance; z is Z 0 Is the characteristic impedance of the transmission line.
As can be seen from the above equation, to eliminate reflections, the matching resistance can be terminated, i.e. ρ is ensured L And=0. Due to the characteristic impedance of the twisted pair being about 120 omega, i.e. Z 0 And approximately 120Ω. Thus, to avoid signal reflection effects, the CAN protocol agrees to maintain impedance continuity across a 120 Ω termination resistor on the bus termination, i.e., R L =120Ω, so that ρ L Approximately 0; it is theoretically considered that signal reflection is almost eliminated.
However, in practical engineering application, the applicant has large difference in length, cable material and the like of the CAN communication cable, so that the impedance difference of the communication cable is large, and the terminal resistance of the communication cable is simply and fixedly set to 120 Ω in the prior art, so that ρ cannot be ensured L Not equal to 0, the CAN communication signal still has larger reflection risk, and certain hidden trouble is brought to the reliability and the stability of the CAN communication.
For this reason, the applicant has sought to improve upon the above technical problems.
Disclosure of Invention
Therefore, the invention aims to provide an automatic configuration method and circuit of the CAN communication terminal resistor, which effectively solve the engineering practical problem caused by mismatching of the terminal resistor and the cable impedance in the CAN communication field and improve the reliability and stability of CAN communication.
For this purpose, the invention adopts the following technical scheme:
an automatic configuration method of CAN communication terminal resistance calculates the impedance Rw of a CAN communication cable, and matches an equivalent terminal resistance based on the impedance Rw of the CAN communication cable, wherein the equivalent terminal resistance=the impedance Rw of the CAN communication cable or the equivalent terminal resistance is approximately equal to the impedance Rw of the CAN communication cable.
Preferably, the method for calculating the impedance Rw of the CAN communication cable includes the following operation steps:
s10), establishing an equivalent circuit of the CAN communication cable and the load impedance RL, under steady-state conditions in the equivalent circuit,wherein U is in Differential output voltage of source end for CAN communication, U out Load terminal voltage for CAN communication, RL is load impedance;
s20), under the condition of ensuring that the CAN communication bus keeps dominant state, the load impedance R is set L Set to a first value R L1 From this, the load terminal voltage U of the first CAN communication is calculated out1 ；
S30), under the condition of ensuring that the CAN communication bus keeps dominant state, loading impedance R L Set to a second value R L2 Thereby calculating the load terminal voltage U of the second CAN communication out2 ；
S40), based on the following formula:
and calculating to obtain the impedance Rw of the CAN communication cable.
Preferably, the second value R L2 Greater than the first value R 1 And the second value R L2 Is the first value R 1 Is a multiple of (2).
Preferably, the first value R L1 =60deg.OMEGA, and isThe second value R L2 ＝120Ω。
Preferably, a terminal resistor matrix module is set through CAN communication, wherein the process of matching the equivalent terminal resistor is as follows: and determining the equivalent termination resistance by taking the impedance Rw of the CAN communication cable or the equivalent termination resistance of the CAN communication cable as a configuration principle, and outputting the equivalent termination resistance by the termination resistance matrix module.
Preferably, an automatic configuration circuit of the CAN communication terminal resistor adopts the automatic configuration method of the CAN communication terminal resistor; the automatic configuration circuit comprises a terminal resistor matrix module, a CAN communication interface module, a voltage sampling module and an MCU module;
the terminal resistor matrix module is connected between the CAN communication signal input end and the CAN communication interface module;
the MCU module is in control connection with the CAN communication interface module;
the voltage sampling module is connected between the output end of the terminal resistor matrix module and the MCU module and is used for collecting the voltage of the CAN communication load end and sending the voltage to the MCU module.
Preferably, the terminal resistor matrix module is connected with a first input end and a second input end of the CAN communication signal respectively; the terminal resistor matrix module comprises a plurality of switching tubes connected between a first input end and a second input end, the switching tubes are correspondingly connected with resistors, and various load resistor states of the terminal resistor matrix module are realized through selective connection of the switching tubes and the corresponding resistors, so that dynamic adjustment of voltage difference signals between the first input end and the second input end of CAN communication signals is realized.
Preferably, the termination resistor matrix module comprises a zero-number switching tube, a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a fifth switching tube, a sixth switching tube, a seventh switching tube and an eighth switching tube; the first switching tube, the second switching tube, the third switching tube, the fourth switching tube, the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube are correspondingly connected with a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor and an eighth resistor respectively, and are used for controlling the selective connection of the corresponding resistors;
the zero switching tube is connected with the second input end;
the first switching tube and the second switching tube are sequentially connected between the first input end and the zero switching tube;
the third switching tube and the fourth switching tube are sequentially connected between the first input end and the zero switching tube;
the fifth switching tube and the sixth switching tube are sequentially connected between the first input end and the zero switching tube;
the seventh switching tube and the eighth switching tube are sequentially connected between the first input end and the zero switching tube.
Preferably, the first resistor, the second resistor, the third resistor, the fourth resistor, the fifth resistor, the sixth resistor, the seventh resistor and the eighth resistor are all 120Ω; through the linkage combination of the zero-number switching tube, the first switching tube, the second switching tube, the third switching tube, the fourth switching tube, the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube, the 11 load resistance states of 240 omega, 180 omega, 160 omega, 150 omega, 120 omega, 100 omega, 90 omega, 80 omega, 70 omega, 60 omega and no-load resistance are realized.
Preferably, the CAN communication interface module converts the CAN communication signal output by the terminal resistor matrix module into a CAN communication data analog signal and is in bidirectional communication connection with the MCU module.
The invention specially develops a method for automatically calculating the impedance Rw of the CAN communication cable by calculating the impedance Rw of the CAN communication cable, and then matches the equivalent termination resistance according to the calculated impedance Rw of the CAN communication cable so as to lead the load reflection coefficient rho L The method has the advantages that the reflection problem of CAN communication is reliably guaranteed to be eliminated or basically eliminated, the engineering practical problem caused by mismatching of the terminal resistor and the cable impedance on the CAN communication site is effectively solved through the innovative scheme provided by the application, and the reliability and the stability of the CAN communication are improved; the invention also developsThe automatic configuration circuit of the CAN communication terminal resistor outputs various load resistor states through the terminal resistor matrix module, so that dynamic adjustment of voltage difference signals between a first input end and a second input end of CAN communication signals is realized, and the load reflection coefficient rho is ensured L =0 or≡0; the automatic configuration circuit provided by the application is simple and reliable in structure and is very suitable for large-scale application in engineering sites.
Drawings
FIG. 1 is an equivalent circuit diagram of a CAN communication cable and load impedance RL according to an embodiment of the application;
fig. 2 is a circuit diagram of automatic configuration of CAN communication termination resistors in accordance with an embodiment of the present application.
Detailed Description
The embodiment of the invention discloses an automatic configuration method of CAN communication terminal resistance, which calculates the impedance Rw of a CAN communication cable and matches an equivalent terminal resistance based on the impedance Rw of the CAN communication cable, wherein the equivalent terminal resistance=the impedance Rw of the CAN communication cable or the equivalent terminal resistance is approximately equal to the impedance Rw of the CAN communication cable.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments described in the present invention, and other drawings may be obtained according to the drawings without inventive effort to those skilled in the art.
The embodiment provides an automatic configuration method of CAN communication terminal resistance, which calculates the impedance Rw of a CAN communication cable, and matches an equivalent terminal resistance based on the impedance Rw of the CAN communication cable, wherein the equivalent terminal resistance=the impedance Rw of the CAN communication cable or the equivalent terminal resistance is approximately equal to the impedance Rw of the CAN communication cable.
Preferably, in the present embodiment, the method for calculating the impedance Rw of the CAN communication cable includes the following steps:
s10), referring to fig. 1, an equivalent circuit of the CAN communication cable and the load impedance RL is established,
under steady state conditions in the equivalent circuit, the equivalent circuit has the following derivation:
finally, the method can obtain:
wherein CAN_H is the first input end of the CAN communication signal, CAN_L is the second input end of the CAN communication signal, U in Differential output voltage of source end for CAN communication, U out The load terminal voltage is the load terminal voltage of CAN communication, rin is the source terminal impedance, RL is the load impedance, and Rw is the impedance of a communication cable; u (U) in For the differential output voltage of the CAN communication source end (namely the original voltage difference signal between the CAN_H and the CAN_L), U out The voltage of the CAN communication load terminal is the voltage;
s20), under the condition of ensuring that the CAN communication bus keeps dominant state, the load impedance R is set L Set to a first value R L1 From this, the load terminal voltage U of the first CAN communication is calculated out1 ；
S30), under the condition of ensuring that the CAN communication bus keeps dominant state, loading impedance R L Set to a second value R L2 By the following constitutionThe load terminal voltage U of the second CAN communication is calculated out2 ；
Further preferably, in order to improve the automatic calculation efficiency, in the present embodiment, the second value R L2 Is greater than a first value R 1 And a second value R L2 Is a first value R 1 Is a multiple of (2); particularly preferably, in the present embodiment, the first value R L1 =60deg.OMEGA, and a second value R L2 ＝120Ω；
S40), based on the following formula:
the impedance Rw of the CAN communication cable is calculated, and the specific calculation process in this embodiment is as follows:
by known measured U out1 And U out2 The impedance Rw of the CAN communication cable CAN be calculated.
Preferably, in order to quickly and accurately match the equivalent termination resistance, in this embodiment, a termination resistance matrix module is set through CAN communication, where the process of matching the equivalent termination resistance is: and determining an equivalent termination resistance (equivalent to load resistance RL) by taking the impedance Rw of the equivalent termination resistance=CAN communication cable or the impedance Rw of the equivalent termination resistance (approximately equal to CAN communication cable) as a configuration principle, and outputting the equivalent termination resistance by a termination resistance matrix module.
Preferably, referring to fig. 2, an automatic configuration circuit of a CAN communication terminal resistor adopts the automatic configuration method of the CAN communication terminal resistor as described above; the automatic configuration circuit comprises a terminal resistor matrix module 1, a CAN communication interface module 2, a voltage sampling module 3 and an MCU module 4;
the terminal resistor matrix module 1 is connected between a CAN communication signal input end (specifically, a first input end CAN_H of a CAN communication signal and a second input end CAN_L of the CAN communication signal) and the CAN communication interface module 2;
the MCU module 4 is in control connection with the CAN communication interface module 2;
the voltage sampling module 3 is connected between the voltage output end U+ of the terminal resistor matrix module 1 and the MCU module 4 and is used for collecting the voltage U of the CAN communication load end out And sent to the MCU module 4.
Preferably, the terminal resistor matrix module 1 is connected with a first input end CAN_H and a second input end CAN_L of the CAN communication signal respectively; the termination resistor matrix module 1 comprises a plurality of switching tubes connected between the first input end CAN_H and the second input end CAN_L, wherein each switching tube corresponds to a connection resistor, and multiple load resistor states of the termination resistor matrix module 1 are realized by selectively switching on the corresponding resistor of each switching tube, so that a voltage difference signal (equivalent to a differential output voltage U of a CAN communication source end) between the first input end CAN_H and the second input end CAN_L of a CAN communication signal is realized in ) Dynamic adjustment of (3).
Preferably, the termination resistor matrix module 1 comprises a zero-number switching tube Q0, a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, a fourth switching tube Q4, a fifth switching tube Q5, a sixth switching tube Q6, a seventh switching tube Q7 and an eighth switching tube Q8; the first switching tube Q1, the second switching tube Q2, the third switching tube Q3, the fourth switching tube Q4, the fifth switching tube Q5, the sixth switching tube Q6, the seventh switching tube Q7 and the eighth switching tube Q8 are correspondingly connected with a first resistor RL1, a second resistor RL2, a third resistor RL3, a fourth resistor RL4, a fifth resistor RL5, a sixth resistor RL6, a seventh resistor RL7 and an eighth resistor RL8 respectively, and are used for controlling the selective connection of the corresponding resistors;
the zero switching tube Q0 is connected with the second input end CAN_L;
the first switching tube Q1 and the second switching tube Q2 are sequentially connected between the first input end CAN_H and the zero switching tube Q0;
the third switching tube Q3 and the fourth switching tube Q4 are sequentially connected between the first input end CAN_H and the zero switching tube Q0;
the fifth switching tube Q5 and the sixth switching tube Q6 are sequentially connected between the first input end CAN_H and the zero switching tube Q0;
the seventh switching tube Q7 and the eighth switching tube Q8 are sequentially connected between the first input end CAN_H and the zero switching tube Q0.
Preferably, the first, second, third, fourth, fifth, sixth, seventh and eighth resistances RL1, RL2, RL3, RL4, RL5, RL6, RL7 and RL8 are each 120Ω; the linkage combination of the zero-number switching tube Q0, the first switching tube Q1, the second switching tube Q2, the third switching tube Q3, the fourth switching tube Q4, the fifth switching tube Q5, the sixth switching tube Q6, the seventh switching tube Q7 and the eighth switching tube Q8 realizes the 11 load resistance states of 240 omega, 180 omega, 160 omega, 150 omega, 120 omega, 100 omega, 90 omega, 80 omega, 70 omega, 60 omega and no-load resistance.
Preferably, in this embodiment, the CAN communication interface module 2 converts the CAN communication signals (adjusted can_h and can_l) output by the terminal resistor matrix module 1 into CAN communication data analog signals can_rxd and can_txd, and performs bidirectional communication connection with the MCU module 4, so as to implement bidirectional data exchange.
This example ensures that the load reflection coefficient ρ is reduced by the above embodiment L The method has the advantages that the reflection problem of CAN communication is reliably guaranteed to be eliminated or basically eliminated, the engineering practical problem caused by mismatching of the terminal resistor and the cable impedance in the CAN communication field is effectively solved, and the reliability and the stability of CAN communication are improved.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.
Claims (10)
1. The automatic configuration method of the CAN communication terminal resistor is characterized by calculating the impedance Rw of a CAN communication cable and matching the equivalent terminal resistor based on the impedance Rw of the CAN communication cable, wherein the equivalent terminal resistor=the impedance Rw of the CAN communication cable or the equivalent terminal resistor is approximately equal to the impedance Rw of the CAN communication cable.
2. The automatic configuration method of CAN communication terminal resistor according to claim 1, wherein the calculation method of the impedance Rw of the CAN communication cable comprises the following operation steps:
s10), establishing an equivalent circuit of the CAN communication cable and the load impedance RL, under steady-state conditions in the equivalent circuit,wherein U is in Differential output voltage of source end for CAN communication, U out Load terminal voltage for CAN communication, RL is load impedance;
s20), under the condition of ensuring that the CAN communication bus keeps dominant state, the load impedance R is set L Set to a first value R L1 From this, the load terminal voltage U of the first CAN communication is calculated out1 ；
S30), under the condition of ensuring that the CAN communication bus keeps dominant state, loading impedance R L Set to a second value R L2 Thereby calculating the second CANLoad terminal voltage U of communication out2 ；
S40), based on the following formula:
and calculating to obtain the impedance Rw of the CAN communication cable.
3. The automatic configuration method of CAN communication terminal resistor according to claim 2, wherein the second value R L2 Greater than the first value R 1 And the second value R L2 Is the first value R 1 Is a multiple of (2).
4. The method for automatically configuring a CAN communication terminal resistor according to claim 3, wherein the first value R L1 =60deg.OMEGA, and the second value R L2 ＝120Ω。
5. The automatic configuration method of CAN communication terminal resistor according to claim 1, wherein the terminal resistor matrix module is set in CAN communication, and the process of matching equivalent terminal resistor is as follows: and determining the equivalent termination resistance by taking the impedance Rw of the CAN communication cable or the equivalent termination resistance of the CAN communication cable as a configuration principle, and outputting the equivalent termination resistance by the termination resistance matrix module.
6. An automatic configuration circuit of a CAN communication terminal resistor, characterized in that an automatic configuration method of the CAN communication terminal resistor according to any one of claims 1 to 5 is adopted; the automatic configuration circuit comprises a terminal resistor matrix module, a CAN communication interface module, a voltage sampling module and an MCU module;
the terminal resistor matrix module is connected between the CAN communication signal input end and the CAN communication interface module;
the MCU module is in control connection with the CAN communication interface module;
the voltage sampling module is connected between the output end of the terminal resistor matrix module and the MCU module and is used for collecting the voltage of the CAN communication load end and sending the voltage to the MCU module.
7. The automatic configuration circuit of CAN communication terminal resistor according to claim 6, wherein the terminal resistor matrix module is connected with a first input terminal and a second input terminal of CAN communication signal, respectively; the terminal resistor matrix module comprises a plurality of switching tubes connected between a first input end and a second input end, the switching tubes are correspondingly connected with resistors, and various load resistor states of the terminal resistor matrix module are realized through selective connection of the switching tubes and the corresponding resistors, so that dynamic adjustment of voltage difference signals between the first input end and the second input end of CAN communication signals is realized.
8. The automatic configuration circuit of CAN communication terminal resistor according to claim 7, wherein the terminal resistor matrix module comprises a zero-number switching tube, a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a fifth switching tube, a sixth switching tube, a seventh switching tube and an eighth switching tube; the first switching tube, the second switching tube, the third switching tube, the fourth switching tube, the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube are correspondingly connected with a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor and an eighth resistor respectively, and are used for controlling the selective connection of the corresponding resistors;
the zero switching tube is connected with the second input end;
the first switching tube and the second switching tube are sequentially connected between the first input end and the zero switching tube;
the third switching tube and the fourth switching tube are sequentially connected between the first input end and the zero switching tube;
the fifth switching tube and the sixth switching tube are sequentially connected between the first input end and the zero switching tube;
the seventh switching tube and the eighth switching tube are sequentially connected between the first input end and the zero switching tube.
9. The automatic configuration circuit of CAN communication termination resistors of claim 8, wherein the first resistor, the second resistor, the third resistor, the fourth resistor, the fifth resistor, the sixth resistor, the seventh resistor, and the eighth resistor are all 120Ω; through the linkage combination of the zero-number switching tube, the first switching tube, the second switching tube, the third switching tube, the fourth switching tube, the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube, the 11 load resistance states of 240 omega, 180 omega, 160 omega, 150 omega, 120 omega, 100 omega, 90 omega, 80 omega, 70 omega, 60 omega and no-load resistance are realized.
10. The automatic configuration circuit of CAN communication terminal resistor according to claim 6, wherein the CAN communication interface module converts CAN communication signals output by the terminal resistor matrix module into CAN communication data analog signals and performs bidirectional communication connection with the MCU module.
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