Physical layer CAN bus repeater
By introducing a CAN bus closed-loop feedback suppression circuit and a digital isolator into the CAN bus repeater, the problems of bus dominant level clamping and signal delay are solved, achieving low-latency, high-efficiency data transmission and network stability, and ensuring the normal operation and transparent access of the CAN bus.
Patent Information
- Application Number
- CN202510988435.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-17
- Publication Date
- 2025-11-21
AI Technical Summary
Existing physical layer CAN bus repeaters lack CAN bus closed-loop feedback suppression functionality, resulting in bus dominant level clamping, which may lead to arbitration failure and bus paralysis; another type of repeater has a signal flow through more layers, increasing signal transmission delay and affecting the effective transmission distance of the bus.
By employing a CAN bus closed-loop feedback suppression circuit and a digital isolator, the data receiving and transmitting ends of the first CAN transceiver are cross-connected with the data receiving and transmitting ends of the second CAN transceiver through the CAN bus closed-loop feedback suppression circuit and digital isolator. A single-channel buffer with three-state control is used to realize channel control, eliminate closed-loop feedback, and reduce signal propagation delay.
It achieves low-latency, high-speed data transmission, prevents bus failure, ensures the normal operation of the CAN network, isolates the electrical interference between the two relay networks, and maintains the transparency of the network.
Smart Images
Figure CN121000548A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of CAN communication technology, and in particular to a physical layer CAN bus repeater. Background Technology
[0002] Based on publicly available patents, existing physical layer CAN bus repeaters mainly take two forms: one is to directly cross-connect the data receiving end (RXD) and data transmitting end (TXD) of two CAN transceivers; the other is to cross-connect the data receiving end (RXD) and data transmitting end (TXD) of two CAN transceivers after passing through a circuit such as an automatic signal flow switching circuit.
[0003] The first type of CAN bus repeater lacks the CAN bus closed-loop feedback suppression function. According to the CAN bus communication protocol and the characteristics of self-feedback, it will cause the bus dominant level to be clamped, which will eventually lead to the failure of bus arbitration or even bus paralysis.
[0004] The automatic switching circuit in the second type of CAN bus repeater causes the signal to flow through more levels, increasing the signal transmission delay and affecting the effective transmission distance of the bus. Summary of the Invention
[0005] In view of the above problems, the present invention provides a physical layer CAN bus repeater for overcoming or at least partially solving the above problems.
[0006] This invention provides the following solution:
[0007] A physical layer CAN bus repeater, comprising:
[0008] A first CAN transceiver and a second CAN transceiver; the first data receiving end and the first data transmitting end of the first CAN transceiver are cross-connected with the second data receiving end and the second data transmitting end of the second CAN transceiver through a CAN bus closed-loop feedback suppression circuit and a digital isolator, so that data can be relayed between the CAN network where the first CAN transceiver is located and the CAN network where the second CAN transceiver is located.
[0009] The CAN bus closed-loop feedback suppression circuit includes a first single-channel buffer and a second single-channel buffer with three-state control; the first single-channel buffer is used to implement channel control between the first data receiving end and the second data transmitting end; the second single-channel buffer is used to implement channel control between the second data receiving end and the first data transmitting end.
[0010] Preferably, the enable terminal of the first single-channel buffer is connected to the second data receiving terminal. When the second data receiving terminal is at a high level, the output of the first single-channel buffer is equal to the input. When the second data receiving terminal is at a low level, the output of the first single-channel buffer is in a high-impedance state.
[0011] Preferably, the enable terminal of the second single-channel buffer is connected to the first data receiving terminal. When the first data receiving terminal is at a high level, the output of the second single-channel buffer is equal to the input. When the first data receiving terminal is at a low level, the output of the second single-channel buffer is in a high-impedance state.
[0012] Preferably, the CAN bus terminal of the first CAN transceiver is connected to the first CAN network, and the CAN bus terminal of the second CAN transceiver is connected to the second CAN network.
[0013] Preferably, when the first CAN network and the second CAN network are idle, the first data receiving end and the first data transmitting end are both at a high level, the output of the single-channel buffer with tri-state control is equal to the input, and the second data receiving end and the second data transmitting end are at a high level.
[0014] Preferably, when the first CAN transceiver receives a data bit from the first CAN network, the data bit is output by the data receiving end of the first CAN transceiver, transmitted to the second data transmitting end via the first single-channel buffer, and then transmitted by the second CAN transceiver to the second CAN network via the CAN bus, thereby realizing data relay transmission from the first CAN network to the second CAN network; similarly, relay from the second CAN network to the first CAN network can be realized.
[0015] Preferably, when the data bit is determined to be 0, the output of the second single-channel buffer is in a high-impedance state, cutting off the closed-loop feedback path from the first data receiver to the second data transmitter to the second data receiver to the first data transmitter in the repeater.
[0016] Preferably, the digital isolator is used to disconnect the electrical connection between the first CAN network and the second CAN network while maintaining data communication, to prevent mutual electrical interference between the two CAN networks.
[0017] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:
[0018] This application provides a physical layer CAN bus repeater with low latency and effective guarantee of high-speed data transmission in the CAN network. The repeater has very few latency stages, minimizing relay delays and effectively ensuring high-speed data transmission between the two CAN networks being relayed. Its feedback suppression function prevents closed-loop feedback that could paralyze the CAN bus between the two relayed networks, ensuring continuous and normal operation of the CAN bus. The repeater can be "transparently" connected to two CAN networks requiring relay, maintaining data communication while isolating the electrical interference between the two relayed CAN networks. It does not involve software layers and is transparent to the two relayed CAN networks.
[0019] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.
[0021] Figure 1 This is a connection block diagram of a physical layer CAN bus repeater provided in an embodiment of the present invention;
[0022] Figure 2 This is a schematic diagram of unsuppressed CAN bus closed-loop feedback provided in an embodiment of the present invention. Detailed Implementation
[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.
[0024] See Figure 1 This is a physical layer CAN bus repeater provided in an embodiment of the present invention, such as... Figure 1 As shown, the repeater may include:
[0025] A first CAN transceiver and a second CAN transceiver; the first data receiving end and the first data transmitting end of the first CAN transceiver are cross-connected with the second data receiving end and the second data transmitting end of the second CAN transceiver through a CAN bus closed-loop feedback suppression circuit and a digital isolator, so that data can be relayed between the CAN network where the first CAN transceiver is located and the CAN network where the second CAN transceiver is located.
[0026] The CAN bus closed-loop feedback suppression circuit includes a first single-channel buffer and a second single-channel buffer with three-state control; the first single-channel buffer is used to implement channel control between the first data receiving end and the second data transmitting end; the second single-channel buffer is used to implement channel control between the second data receiving end and the first data transmitting end.
[0027] The physical layer CAN bus repeater provided in this application consists of two CAN transceivers whose data receiving ends (RXD) and data transmitting ends (TXD) are cross-connected via a CAN bus closed-loop feedback suppression circuit. This eliminates the problem of dominant level clamping on the bus, thereby preventing the risk of bus paralysis caused by dominant level clamping. Furthermore, the bus closed-loop suppression circuit of this CAN bus repeater contains only one stage of digital buffer and one stage of digital isolator, minimizing signal propagation delay and having virtually no impact on the bus transmission distance. In addition, this CAN bus repeater has a dominant timeout protection function.
[0028] In a specific implementation, the embodiment of this application can provide that the enable terminal of the first single-channel buffer is connected to the second data receiving terminal. When the second data receiving terminal is at a high level, the output of the first single-channel buffer is equal to the input. When the second data receiving terminal is at a low level, the output of the first single-channel buffer is in a high-impedance state.
[0029] The enable terminal of the second single-channel buffer is connected to the first data receiving terminal. When the first data receiving terminal is at a high level, the output of the second single-channel buffer is equal to the input. When the first data receiving terminal is at a low level, the output of the second single-channel buffer is in a high-impedance state.
[0030] In the specific construction of the network, the embodiments of this application may provide that the CAN bus terminal of the first CAN transceiver is connected to the first CAN network, and the CAN bus terminal of the second CAN transceiver is connected to the second CAN network.
[0031] When the first CAN network and the second CAN network are idle, the first data receiver and the first data transmitter are both at a high level, the output of the single-channel buffer with tri-state control is equal to the input, and the second data receiver and the second data transmitter are at a high level.
[0032] When the first CAN transceiver receives a data bit from the first CAN network, the data bit is output by the first data receiving end, transmitted to the second data transmitting end via the first single-channel buffer, and then transmitted by the second CAN transceiver to the second CAN network via the CAN bus, thus realizing the relay from the first CAN network to the second CAN network.
[0033] When the data bit is determined to be 0, the output of the second single-channel buffer is in a high-impedance state, cutting off the closed-loop feedback path from the first data receiver to the second data transmitter to the second data receiver to the first data transmitter in the repeater.
[0034] The digital isolator is used to disconnect the electrical connection between the first CAN network and the second CAN network while maintaining data communication.
[0035] The physical layer CAN bus repeater provided in this application will be described in detail below.
[0036] The specific implementation of the physical layer CAN bus repeater (hereinafter referred to as "repeater") provided in this application embodiment is as follows: Figure 1 As shown.
[0037] The repeater includes a first CAN transceiver and a second CAN transceiver (both of which are transceivers with explicit timeout protection). The first CAN transceiver includes a first data receiver RXD1 and a second data receiver RXD2.
[0038] The receive data output terminal RXD and transmit data input terminal TXD of the first CAN transceiver and the second CAN transceiver are cross-connected after passing through the CAN bus closed-loop feedback suppression circuit (hereinafter referred to as "feedback suppression circuit") and the high-speed digital isolator. The CAN bus terminals of the first CAN transceiver and the second CAN transceiver are connected to the first CAN network A and the second CAN network B, respectively. The first CAN network A and the first CAN transceiver form a new first CAN network A′, and the second CAN network B and the second CAN transceiver form a new second CAN network B′. (The terminating resistor configuration in the first CAN network A′ and the second CAN network B′ is configured according to the actual situation and will not be described in detail.)
[0039] During operation, the data bits received by the first CAN transceiver from the bus of the first CAN network A are output from the first data receiving terminal RXD1. After passing through the buffer and digital isolator in the feedback suppression circuit, they are received by the second data transmitting terminal TXD2 of the second transceiver and transmitted to the bus of the second CAN network B. Similarly, the data bits received by the second CAN transceiver from the bus of the second CAN network B can be transmitted to the bus of the first CAN network A after passing through the repeater. In this way, the repeater realizes the relay function between the first CAN network A and the second CAN network B.
[0040] According to the operating characteristics of the CAN bus, each node containing a CAN controller in the first CAN network A and the second CAN network B can detect the actual voltage level on the bus in real time. The CAN controller of that node compares this level with its own transmitted voltage level to determine if the transmission and reception are consistent. Therefore, when the data bits received by the first CAN transceiver from the first CAN network A are transmitted to the second CAN network B via the second transceiver, the data bit transmission path is: first data receiver RXD1 -> second data transmitter TXD2 (simultaneously transmitting to the second CAN network B) -> second data receiver RXD2 -> first data transmitter TXD1 (simultaneously transmitting to the first CAN network A) -> first data receiver RXD1. This forms a closed-loop feedback between the two transceivers of the repeater (e.g., ...). Figure 2 (As shown by the dashed arrow in the diagram), this causes the signal to circulate between the two transceivers, and then circulate between the first CAN network A and the second CAN network B, forming a positive feedback loop.
[0041] Similarly, when the signal bit received by the second CAN transceiver from the second CAN network B is transmitted to the first CAN network A via transceiver 1, the transmission path of the signal bit is: second data receiver RXD2 → first data transmitter TXD1 (sends to the first CAN network A simultaneously) → first data receiver RXD1 → second data transmitter TXD2 (sends to the second CAN network B simultaneously) → second data receiver RXD2. This also forms a closed loop feedback between the two transceivers of the repeater, causing the signal to be circulated between the two transceivers, and then circulated between the first CAN network A and the second CAN network B.
[0042] When a low-level (dominant) data bit appears during relay transmission, due to the wired-AND characteristic of the CAN bus, this positive feedback loop will cause a continuous dominant level on the bus, and this state cannot be broken even when the next data bit is high (recessive). Ultimately, this causes the bus arbitration to fail and will affect the communication of all nodes in the first CAN network A' and the second CAN network B', even leading to bus paralysis. Therefore, the closed-loop feedback of the CAN bus must be suppressed to ensure the continuous normal operation of the CAN bus.
[0043] The feedback suppression circuit in this application consists of two single-channel buffers, a first single-channel buffer B1 and a second single-channel buffer B2, both with tri-state control (e.g., Figure 1 As shown in Table 1, the first single-channel buffer B1 controls the channel between the first data receiver RXD1 and the second data transmitter TXD2. Its enable terminal is connected to the second data receiver RXD2. When the second data receiver RXD2 is high, the output of the first single-channel buffer B1 is equal to the input. When the second data receiver RXD2 is low, the output of the first single-channel buffer B1 is in a high-impedance state. The second single-channel buffer B2 controls the channel between the second data receiver RXD2 and the first data transmitter TXD1. Its enable terminal is connected to the first data receiver RXD1. When the first data receiver RXD1 is high, the output of the second single-channel buffer B2 is equal to the input. When the first data receiver RXD1 is low, the output of the second single-channel buffer B2 is in a high-impedance state. The truth table of the feedback suppression circuit is shown in Table 1.
[0044] Table 1 Truth Table of Feedback Suppression Circuit
[0045]
[0046] When the first CAN network A and the second CAN network B are idle, the first data receiver RXD1 and the first data transmitter TXD1 are both at high level. Then En1 and En2 are also at high level. The output of the single-channel first single-channel buffer B1 and the second single-channel buffer B2 with tri-state control is equal to the input. The second data receiver RXD2 and the second data transmitter TXD2 are also at high level.
[0047] When the first CAN transceiver receives a data bit from the first CAN network A, the data bit is output by the first data receiver RXD1, transmitted to the second data transmitter TXD2 via the first single-channel buffer B1, and then transmitted by the second CAN transceiver to the second CAN network B via the CAN bus, realizing the relay from the first CAN network A to the second CAN network B. If this data bit is "0", then En2 = 0, the output of the second single-channel buffer B2 is in a high-impedance state, cutting off the closed-loop feedback path in the repeater from the first data receiver RXD1 to the second data transmitter TXD2, thus solving the problem of the bus not working properly due to the continuous dominant level caused by the closed-loop feedback when transmitting a dominant level (i.e., realizing "closed-loop feedback suppression"). Similarly, when the second CAN transceiver receives a data bit from the second CAN network B, it can relay the data bit to the first CAN network A and realize closed-loop feedback suppression.
[0048] When the first CAN transceiver and the second CAN transceiver simultaneously receive data bits, relay transmission is performed between the first CAN network A and the second CAN network B according to the mechanism corresponding to state 4 in Table 1.
[0049] There is a special case that needs to be explained here: When the first CAN network A and the second CAN network B simultaneously transmit data bits "0" to each other via repeaters, the outputs of the first single-channel buffer B1 and the second single-channel buffer B2 are both in a high-impedance state, which may affect the transmission of data bits "0" between the two CAN networks. When this happens, it indicates that a node in the first CAN network A and a node in the second CAN network B simultaneously send out data bits "0". Due to the feedback received by the CAN transceiver and the "wired-AND" characteristic, the buses of both the first CAN network A and the second CAN network B will be dominant. This means that each node in both the first CAN network A and the second CAN network B can receive data bits "0". Thus, although the communication path between the first CAN transceiver and the second CAN transceiver is blocked due to closed-loop feedback suppression, it is still equivalent to receiving data bits "0", and therefore it will not affect the transmission of data bits "0" between the two CAN networks.
[0050] The digital isolator between the first CAN transceiver and the second CAN transceiver disconnects the electrical connection between the first CAN network A and the second CAN network B while maintaining data communication, thus eliminating mutual electrical interference between the two CAN networks.
[0051] In summary, the physical layer CAN bus repeater provided in this application has low latency and can effectively ensure high-speed data transmission in the CAN network. The repeater has very few latency stages, minimizing relay delays and effectively guaranteeing high-speed data transmission between the two CAN networks being relayed. The repeater's feedback suppression function prevents closed-loop feedback that could paralyze the CAN bus between the two relayed networks, ensuring the continuous normal operation of the CAN bus. It can be "transparently" connected to two CAN networks requiring relay. While maintaining data communication, the repeater isolates the electrical mutual interference between the two relayed CAN networks and does not involve the software layer, making it transparent to the two CAN networks being relayed.
[0052] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0053] As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that this application can be implemented by means of software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments of this application.
[0054] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the descriptions in the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.
[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.
Claims
1. A physical layer CAN bus repeater, characterized in that, It includes a first CAN transceiver and a second CAN transceiver; the first data receiving end and the first data sending end of the first CAN transceiver are cross-connected with the second data receiving end and the second data sending end of the second CAN transceiver through a CAN bus closed-loop feedback suppression circuit and a digital isolator, so that data can be relayed between the CAN network where the first CAN transceiver is located and the CAN network where the second CAN transceiver is located. The CAN bus closed-loop feedback suppression circuit includes a first single-channel buffer and a second single-channel buffer with three-state control; the first single-channel buffer is used to implement channel control between the first data receiving end and the second data transmitting end; the second single-channel buffer is used to implement channel control between the second data receiving end and the first data transmitting end.
2. The physical layer CAN bus repeater according to claim 1, characterized in that, The enable terminal of the first single-channel buffer is connected to the second data receiving terminal. When the second data receiving terminal is at a high level, the output of the first single-channel buffer is equal to the input. When the second data receiving terminal is at a low level, the output of the first single-channel buffer is in a high-impedance state.
3. The physical layer CAN bus repeater according to claim 1, characterized in that, The enable terminal of the second single-channel buffer is connected to the first data receiving terminal. When the first data receiving terminal is at a high level, the output of the second single-channel buffer is equal to the input. When the first data receiving terminal is at a low level, the output of the second single-channel buffer is in a high-impedance state.
4. The physical layer CAN bus repeater according to claim 1, characterized in that, The CAN bus terminal of the first CAN transceiver is connected to the first CAN network, and the CAN bus terminal of the second CAN transceiver is connected to the second CAN network.
5. The physical layer CAN bus repeater according to claim 4, characterized in that, When the first CAN network and the second CAN network are idle, the first data receiver and the first data transmitter are both at a high level, the output of the single-channel buffer with tri-state control is equal to the input, and the second data receiver and the second data transmitter are at a high level.
6. The physical layer CAN bus repeater according to claim 4, characterized in that, When the first CAN transceiver receives a data bit from the first CAN network, the data bit is output by the data receiving end of the first CAN transceiver, transmitted to the second data transmitting end through the first single-channel buffer, and then transmitted by the second CAN transceiver to the second CAN network via the CAN bus, thus realizing data relay transmission from the first CAN network to the second CAN network; similarly, relay from the second CAN network to the first CAN network can be realized.
7. The physical layer CAN bus repeater according to claim 6, characterized in that, When the data bit is determined to be 0, the output of the second single-channel buffer is in a high-impedance state, cutting off the closed-loop feedback path from the first data receiver to the second data transmitter to the second data receiver to the first data transmitter in the repeater.
8. The physical layer CAN bus repeater according to claim 4, characterized in that, The digital isolator is used to disconnect the electrical connection between the first CAN network and the second CAN network while maintaining data communication, to prevent mutual electrical interference between the two CAN networks.