CN1540889A - A Ring Fiber CAN Bus Network - Google Patents

Abstract

The invention relates to a ring-shaped optical fiber CAN bus network. A CAN transceiver is not used in the ring-shaped CAN bus network, and an optical fiber is used as a transmission medium in the ring-shaped CAN bus network. On the ring fiber CAN network, each CAN node includes a photoelectric conversion module and an interface dedicated to the ring fiber CAN network. The annular optical fiber CAN bus network of the present invention can eliminate the blockage problem of the annular optical fiber CAN network, and the whole optical fiber CAN network has reliable communication, simple circuit and strong anti-interference performance. Therefore, the anti-interference ability of the optical fiber CAN network is better than that of the current twisted pair CAN network, and meets the needs of harsh industrial sites.

Description

A Ring Fiber CAN Bus Network

                      

The invention belongs to CAN bus network, in particular to a circular CAN bus network whose transmission medium is based on optical fiber.

Background technique

CAN (Control Area Network) bus is a serial multi-master controller local bus, which has good network security, communication reliability and real-time performance, and low network cost. Especially suitable for automotive and various industrial control fields. The network can work in the industrial environment with harsh environment, strong electromagnetic radiation and large vibration. The transmission medium can be twisted pair, coaxial cable or optical fiber, and the data transmission rate can reach 1Mbits/s. At present, the twisted-pair CAN bus has been widely used, and the technologies of the twisted-pair CAN bus have been very mature. The twisted-pair CAN bus often uses CAN transceivers such as 82C250 to complete level conversion, and convert the logic level output by the CAN controller into a differential signal with strong anti-interference ability to complete the sending and receiving of messages. The twisted-pair CAN bus network can improve the anti-interference ability of the bus to a certain extent. But when the working environment is particularly complicated, its anti-interference ability is not very satisfactory.

In order to solve the problem of large-capacity, high-speed, and long-distance data transmission in modern communication networks, optical fiber communication networks have been produced. Compared with twisted pair and coaxial cable, another superior performance of optical fiber - strong anti-electromagnetic interference ability has attracted people's attention. In order to further improve the performance of the CAN network, it is necessary to use optical fiber as the transmission medium. At present, due to the high technical difficulty, various technologies of the optical fiber CAN network have not been successfully developed, so they have not been widely used. However, if the CAN transceiver is used in the optical fiber CAN network, it will bring a large delay to the network and make the performance of the network worse.

As a kind of industrial low-level control local area network, the optical fiber CAN network has the same topological structure as the commonly used local area network. The basic topological structures include bus, ring and star. Due to the unidirectionality of optical transmission, the ring network structure becomes one of the important networking schemes.

Contents of the invention

The technical problem to be solved by the present invention is to design an optical fiber CAN ring network interface and construct a ring optical fiber CAN bus network. Among them, the function of the optical fiber ring network interface circuit is: support the CAN bus controller link layer communication protocol, complete the normal sending, receiving and forwarding functions of messages in the ring network, and at the same time improve the anti-interference ability of the CAN bus and reduce the transmission delay.

The technical scheme adopted by the present invention to solve the above-mentioned technical problems is: the CAN transceiver is not used in the ring CAN bus network.

The interconnection in the ring network interface circuit adopts electrical connection, and the specific connection relationship is:

The output TX0 of the CAN controller of each node is connected to the input terminal of a NAND gate b, and is connected to the other input terminal of the NAND gate b through a delay module a, and is also connected to the input terminal of an AND gate d;

An OR gate c input terminal is respectively connected to the input RX0 of the CAN controller and the output terminal of the NAND gate b, and its output terminal is connected to the other input terminal of the AND gate d;

The output of the AND gate d is connected to the LED of the electro-optical conversion module;

The input RX0 of the CAN controller is also connected with the photoelectric conversion module PIN.

Each CAN node in the ring network is electrically connected to the ring network interface circuit; each CAN node forms a ring optical fiber CAN bus network through the ring network interface circuit and optical fiber.

The LED of the electro-optical conversion module of the CAN controller of the sending node is connected with the PIN of the photoelectric conversion module of the CAN controller of the receiving node;

The electro-optical conversion module LED of the receiving node CAN controller is connected with the PIN of the photoelectric conversion module of the downstream receiving node CAN controller in such a cycle, and the electro-optical conversion module LED of the last receiving node CAN controller is connected with the photoelectric conversion module PIN of the sending node CAN controller. Form a ring network.

In order to abide by the protocol of the CAN bus controller in the link layer, an optical fiber ring network interface is designed. The function of the ring network interface is: send and receive messages to the master node on the CAN bus, but not forward the received messages, eliminate the self-excitation phenomenon of the ring fiber CAN bus network, and ensure that the ring network is not blocked; The slave nodes on the CAN bus realize the reception and forwarding of messages, so that the downstream nodes of the ring network can receive the messages of the upstream nodes; the CAN bus response frame information is received and blocked in time to ensure that the response frame information on the bus is transmitted to the The sending node implements a normal message transmission protocol; a simple RC charging and discharging circuit is used to form a delay circuit to generate a delay signal slightly longer than the loop transmission delay to solve the problem of network congestion caused by the self-excitation phenomenon of the ring network.

The invention does not need to use a CAN transceiver, and directly connects the CAN controller to the ring optical fiber network through the ring network interface, which not only reduces the bus transmission delay, but also improves the anti-interference ability of the bus. The adoption of the optical fiber ring network greatly improves the security, communication reliability and real-time performance of the CAN bus network.

Description of drawings

FIG. 1 is a circuit diagram of a network structure according to an embodiment of the present invention, and a schematic diagram of a ring network interface circuit is shown in a dotted line.

FIG. 2 is a timing diagram of each port level of the node unit in the sending state in the loop.

Fig. 3 is a timing diagram of the level of each port of the node unit in the receiving state in the loop.

Figure 4 is a schematic diagram of the delay circuit in the loop.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and examples, but these examples should not be construed as limiting the present invention.

As shown in Figure 1, the TX and RX levels of the CAN controller are at the TTL level, so level conversion is not required in the ring CAN bus network, and the optical fiber ring network is directly connected by using the electro-optical conversion module LED and the photoelectric conversion module PIN message transmission. In this way, there is no need to use a CAN transceiver, which reduces the transmission delay on the bus and simplifies the ring network interface circuit at the same time. The use of optical fiber as the transmission medium makes the anti-interference performance of the whole system better, and the stability of the whole system is improved.

As shown in Figure 2, it is assumed that in the CAN bus network, node 1 becomes the master node of the network (sends messages) through the competition, and at this time other nodes are all slave nodes (receives messages). TX1 represents the signal sent by the TX end of the CAN controller of the sending node; RX1 represents the signal received by the RX end of the CAN controller of the sending node, delay1 represents the transmission delay of the ring network, and ACK represents the response signal sent by the receiving node on the bus; a1 represents the transmission The delayed waveform of the signal sent by the TX1 terminal of the node CAN controller, delay2 represents the delay of the delay module (delay) in the interface circuit; b1 represents the waveform of the TX1 signal and the NAND of the delayed signal, as or An input signal of the gate makes the c1 terminal always maintain a high level when TX1 sends a frame of information, so that the signal received by the RX1 terminal of the node is no longer forwarded, which solves the problem of network congestion caused by the self-excitation phenomenon of the ring network. For the received acknowledgment signal ACK, the receiving node downstream of the master node will process the signal.

As shown in Figure 3, the RX2 terminal receives the data sent from the upstream node in the ring or the forwarded data, and also receives the response signal ACKr transmitted from the previous node. For this signal, it will communicate with the b2 terminal The signal is ORed and filtered out and not forwarded to the next receiving node; the ACK signal in the timing diagram of TX2 is the response signal sent by the receiving node, and the signal will be transmitted to the next receiving node to be received by the next receiving node but not It will be forwarded again; the d2 terminal is the signal sent to the next ring node, ACK represents the response signal sent by the receiving node, and the response signal ACKr sent from the previous node has been filtered out by the interface circuit . For each other node on the ring network, it works according to this sequence, receiving the signal (including data information and response signal information) transmitted by a node on the ring network, and then forwarding the data information through the interface circuit to filter out the previous node. The transmitted response information will also send the response signal information sent by the node to the bus.

As shown in Figure 4, through the analysis of the timing diagram of the sending node and the receiving node above, it shows that the working mode of the ring network interface circuit of the ring optical fiber CAN bus network conforms to the transmission protocol of the CAN bus link layer, which can ensure that each node of the entire ring normal work. For the ring network interface circuit, the key point is how to determine the parameters of the delay circuit according to the transmission delay of the bus. There are many ways to design the delay circuit, which can be implemented not only by analog circuits but also by digital circuits. Here we take the RC delay circuit as an example to illustrate. Assume that there are four nodes in the ring fiber CAN network. Through the test, the delay of the loop through 4 nodes is 130ns, so when designing the delay circuit, the delay should be greater than the transmission delay of the loop, so that the corresponding data can be processed, otherwise there will be glitches that make the Error in bus telegram transmission.

From the above analysis, the delay circuit needs to meet the following conditions:

T _d <Δτ<T _s

In this inequality, T _d represents the loop transmission delay, Δτ is the delay of the delay circuit, and T _s is the bit period of the transmission signal. Measure the transmission delay of the entire loop for different network nodes, calculate the signal transmission period according to the transmission baud rate of the bus signal, and then determine the delay parameters R and C of the RC delay circuit. In the actual network test, if the bus baud rate is set to 125kbit, the delay time of the delay circuit should be less than 8us and greater than the loop delay of 130ns.

The above conditions meet the delay requirements of the signal. At the same time, because the RC delay circuit has filtering characteristics, the RC should not be too large to avoid filtering out the transmitted signal while meeting the delay requirements. According to the above conditions, the network performance of R=3KΩ and C=82pF is the best in the actual test.

The invention has been tested, and completes compliance with the protocols of the CAN bus at the physical layer and the link layer. It can complete the fast and correct transmission of the message and reduce the bus delay. In the present invention, according to the difference in the number of ring network nodes, the RC parameters are adjusted according to the loop transmission delay and the bus baud rate.

Claims (4)

1, a kind of annular optical fiber CAN bus network, it is characterized in that: do not use CAN transceiver in the annular CAN bus network. 2. The annular optical fiber CAN bus network according to claim 1, characterized in that: the annular CAN bus network uses optical fiber as the transmission medium. 3. The annular optical fiber CAN bus network as claimed in claim 1, characterized in that: the interconnection in the ring network interface circuit adopts electrical connection, and the specific connection relationship is: The output TX0 of each node of the CAN controller in the CAN bus network is connected to the input terminal of a NAND gate b, and is connected to the other input terminal of the NAND gate b through a delay module a, and is also connected to the input terminal of an AND gate d terminal connection; An OR gate c input terminal is respectively connected to the input RX0 of the CAN controller and the output terminal of the NAND gate b, and its output terminal is connected to the other input terminal of the AND gate d; The output of the AND gate d is connected to the LED of the electro-optical conversion module; The input RX0 of the CAN controller is also connected to the photoelectric conversion module PIN; Each CAN node in the ring network is electrically connected to the interface circuit of the ring network. 4. The annular optical fiber CAN bus network as claimed in claim 1, characterized in that: each CAN node forms an annular optical fiber CAN bus network through an optical fiber through a ring network interface circuit, wherein: The conversion module LED of the CAN controller of the sending node is connected with the PIN of the photoelectric conversion module of the CAN controller of the receiving node; The electro-optical conversion module LED of the CAN controller of the receiving node is connected with the PIN of the photoelectric conversion module of the CAN controller of the downstream receiving node in such a cycle, and the electro-optical conversion module LED of the CAN controller of the last receiving node is connected with the photoelectric conversion module PIN of the CAN controller of the sending node. Form a ring network.

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