Serial communication bus circuit

Abstract

The present invention provides a data communication circuit that enables communication with a small number of wires and can automatically terminate even when the wiring (bus) is expanded. [Solution] A serial communication bus circuit 1 for sequentially connecting multiple slave nodes 3 to one master node 2 in serial order, wherein each slave node 3 is equipped with a termination resistor 4, a termination switch 5 for connecting and disconnecting the termination resistor 4 to bus B, and a bus switch 6 for connecting and disconnecting communication from slave node 3 to the next slave node 3, wherein in the initial state the termination switch 5 is connected and the bus switch 6 is disconnected, and based on a command from the master node 2, the slave node 3 disconnects the termination switch 5 and connects the bus switch 6 when the next slave node 3 is connected to it.

Description

[Technical Field]

[0001] This invention relates to a serial communication bus circuit. [Background technology]

[0002] Vehicles are equipped with numerous control devices, which perform independent control on their own, and have traditionally communicated and controlled each other using the CAN (Controller Area Network) protocol.

[0003] In the CAN protocol, control devices are called nodes, and by connecting multiple nodes to a single serial bus, it is possible to send messages and data from one node to another (see, for example, Patent Document 1).

[0004] Figure 5 shows a schematic configuration of a conventional standard CAN bus circuit 101. The conventional CAN bus circuit 101 has a master node 102 and multiple slave nodes 1031-103 on a main bus B that is pre-terminated by a termination resistor 104. n The configuration is such that the terminal slave node 103 is always connected to it. n The system is designed to terminate at that point. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2001-069179 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, conventionally, point-to-point serial communication has been used to transmit communication signals for marine applications (see Figure 6). In point-to-point serial communication, a master node 102 and multiple slave nodes 1031-103 nare connected in parallel by a plurality of dedicated signal lines (buses) B, and the master node 102 is connected to a plurality of slave nodes 1031 to 103 n so as to select one of them and transmit and receive data. Therefore, when trying to add a new control device (node) to the circuit, there is a problem that the number of signal lines (buses) B has to be increased, which is cumbersome. The adoption of serial communication in which node addresses (IDs) are attached to data and transmitted and received in order using a small number of signal lines (buses) B has been considered. However, when adding a new control device (node) for marine use, it is often necessary to add a control device (node) across the cabins (to another cabin), that is, it is often necessary to expand the bus to add a node. When trying to use the conventional CAN bus circuit 101, which is an example of serial communication, it is necessary to check the wiring termination points in the ship's drawings, etc., and manually attach a termination resistor to the end of the added control device (node), which has the problem of complicated processing.

[0007] Therefore, an object of the present invention is to provide a data communication circuit that can communicate with a small number of wirings and can automatically terminate even when the wiring (bus) is expanded.

Means for Solving the Problems

[0008] In order to solve the above problems, the invention according to claim 1 is a serial communication bus circuit for sequentially connecting a plurality of slave nodes to one master node. The slave node includes a termination resistor, a termination switch for connecting and disconnecting the termination resistor to and from the bus, and a bus switch for connecting and disconnecting communication from the slave node to the next slave node. In the initial state, the termination switch is connected and the bus switch is disconnected. Based on a command from the master node, when the next slave node is connected to the slave node, the slave node disconnects the termination switch and connects the bus switch.

[0009] The invention described in claim 2 is a serial communication bus circuit as described in claim 1, characterized in that, when communication from any of the slave nodes is disconnected, the slave node immediately preceding the disconnected slave node connects the termination switch and disconnects the bus switch based on a command from the master node. [Effects of the Invention]

[0010] According to the invention described in claim 1, since it is a serial communication bus circuit that serially connects multiple slave nodes to a master node, it is possible to communicate with a small number of wires. Moreover, each slave node is equipped with a termination resistor, a termination switch, and a bus switch, and is initially set to a terminated state (i.e., the termination switch is connected and the bus switch is disconnected), and when it is determined that the next slave node is connected to a slave node, the termination state is released (i.e., the termination switch is disconnected and the bus switch is connected) based on a command from the master node. Therefore, even when a slave node is added to the end of the circuit to expand the bus, the circuit can be automatically terminated.

[0011] Furthermore, according to the invention described in claim 2, if communication from any slave node is interrupted, the slave node immediately preceding the disconnected slave node is set to a terminated state (i.e., the termination switch is connected and the bus switch is disconnected) based on a command from the master node. Therefore, in conventional CAN bus circuits where each node is connected to the main bus, if the main bus is disconnected midway, the absence of termination resistors can cause data misrecognition and other problems, leading to the entire circuit becoming unstable or even shutting down and becoming unusable. However, in this invention, even if the bus is disconnected midway, communication can be automatically restored up to the intermediate path. [Brief explanation of the drawing]

[0012] [Figure 1]This figure shows a schematic configuration of a serial communication bus circuit according to an embodiment of the present invention. [Figure 2] Figure 1 is a flowchart showing the procedure for registering location information in the serial communication bus circuit. [Figure 3] Figure 1 is a flowchart showing the procedure for adding a slave node to the serial communication bus circuit. [Figure 4] Figure 1 is a flowchart showing the procedure for operational monitoring (especially when a disconnection is detected) in the serial communication bus circuit. [Figure 5] This diagram shows a schematic configuration of a conventional standard CAN bus circuit. [Figure 6] This diagram shows a schematic configuration of a conventional parallel communication system. [Modes for carrying out the invention]

[0013] The present invention will be described below based on the illustrated embodiments.

[0014] Figure 1 is a diagram showing the schematic configuration of a serial communication bus circuit 1 according to an embodiment of the present invention. This serial communication bus circuit 1 is a circuit used to sequentially transmit data to multiple control devices (nodes) via a single bus B, and consists of a master node 2 and multiple slave nodes 31-31. n The system includes a termination resistor 4, a termination switch 5, and a bus switch 6. This embodiment primarily describes a case where multiple control devices (nodes) are devices mounted on a ship as control devices for a communication system that notifies land of the occurrence of an emergency.

[0015] In the serial communication bus circuit 1 according to this embodiment, multiple slave nodes 31-3 are connected to one master node 2. n These are sequentially connected serially via bus B. Master node 2 and slave nodes 31-3 nis a control device (node), specifically, a device such as a satellite communication device mounted on a ship. These control devices (nodes) are, for convenience, divided into a master node (parent device) 2 and slave nodes (child devices) 31 to 3 n and will be described separately. However, since the serial communication bus circuit 1 according to the present invention is a multi-master system, there is no parent-child relationship (superior-inferior) between the master node 2 and the slave nodes 31 to 3 n .

[0016] Each slave node 31 to 3 n has an input port (X port) located on the master node 2 side and an output port (Y port) located on the next slave node side or the terminal side (hereinafter, also collectively referred to as the "expansion side"). The expansion side (Y port) is provided with a termination resistor 4, a termination switch 5, and a bus switch 6.

[0017] The termination switch 5 is a switch for connecting (closing, ON) and disconnecting (releasing, OFF) the termination resistor to the bus B. The bus switch 6 is a switch for connecting (closing, ON) and disconnecting (releasing, OFF) the communication from the slave node 31 to the next slave node 3. When one of the switches is connected, the other switch is disconnected. These switches 5 and 6 are in an initial state where the termination switch 5 is connected and the bus switch 6 is disconnected. Then, when registering the position information of each control device (node) described later, each slave node 31 to 3 n is sequentially set to a state suitable for its position, and the operation of the circuit is started. The basic state of the switch is that in the slave nodes 31 to 3 n-1 not located at the terminal, the termination switch 5 is OFF and the bus switch 6 is ON, and in the slave node 3 n located at the terminal, the termination switch 5 is ON and the bus switch 6 is OFF.

[0018] Next, the specific operation of the serial communication bus circuit 1 according to this embodiment will be described with reference to FIGS. 2 to 4.

[0019] Figure 2 is a flowchart showing the procedure for registering location information in the serial communication bus circuit 1. Location information registration is a process performed when the operation of the circuit is started, and specifically involves n slave nodes 31-3 n Register the location information of each slave node 31-3 n Set switches 5 and 6 to the appropriate position.

[0020] First, as a prerequisite for registering location information, master node 2 will connect to each slave node 31-3 n Register the ID (Step S1). At this point, each slave node 31-3 n The initial state is set, i.e., with termination switch 5 ON and bus switch 6 OFF. Also, through ID registration, master node 2 knows that there are n slave nodes 3. Furthermore, ID registration is preferably performed manually to save time and prevent false detections, but it can also be performed automatically.

[0021] Next, master node 2 scans for the IDs of the registered slave nodes 3 one by one in sequence. First, master node 2 scans for ID 1 (specifically, it sends the question "Is this ID 1?") (step S2). When slave node 31 responds (step S3), master node 2 registers slave node 31 as location number 1 (step S4) and sends a command to slave node 31 to change the state of switches 5 and 6 because the next slave node 3 is connected (step S5). Based on the command from master node 2, slave node 31 turns off termination switch 5 and turns on bus switch 6 (step S6). As a result, slave node 31 is released from termination state and becomes ready to communicate with the next slave node 32.

[0022] Secondly, Master Node 2 scans for ID2 (step S7) and then sends a thread to it. When a response is received from master node 32 (step S8), master node 32 is registered as location number 2 (step S9), and a command is sent to slave node 32 to change the state of switches 5 and 6 because the next slave node 3 is connected (step S10). Based on the command from master node 2, slave node 32 turns off termination switch 5 and turns on bus switch 6 (step S11). As a result, slave node 32 is released from termination state and becomes ready to communicate with the next slave node 33.

[0023] Master node 2 performs the same process as above for ID3 to IDn-1, and slave nodes 33 to 3 n-1 Register the location information of slave nodes 33-3. n-1 When location information is registered, the terminal switch 5 is turned OFF and the bus switch 6 is turned ON based on the above command from master node 2 (not shown). As a result, each slave node 33-3 n-1 The termination state is released, and the next slave node 34-3 n This enables communication with the other party.

[0024] Finally, master node 2 scans for IDn (step S12) and sends it to slave node 3. n When a response is received from (step S13), slave node 3 n The location is registered as position number n (step S14). This completes the position information registration process for slave node 3, and the serial communication bus circuit 1 begins operation. n Although it is located at the end of the circuit, switches 5 and 6 are in their initial state (termination switch 5 is ON and bus switch 6 is OFF), i.e., in the termination state, so they can be operated without any changes.

[0025] Figure 3 is a flowchart showing the procedure for adding slave node 3 to serial communication bus circuit 1. Here, slave nodes 31-3 nThis section describes how to expand circuit 1 by adding one slave node 3 to circuit 1 which already has the above components. Note that when adding slave node 3, the slave node 3 located at the end of the circuit will be added. n Add it to the right side, positioning the added slave node 3 at the end of the circuit.

[0026] At this stage, slave nodes 31-3 n Since the location information registration is complete for slave nodes 31-3 n-1 With termination switch 5 OFF and bus switch 6 ON, slave node 3 n The termination switch 5 is ON and the bus switch 6 is OFF. Also, the additional slave node 3 n+1 Switches 5 and 6 are assumed to be in their initial state (termination switch 5 is ON and bus switch 6 is OFF).

[0027] First, master node 2 registers IDn+1 of the slave node 3 to be added (step S15). Then, with the addition of a new slave node 3, slave node 3 is no longer at the end of the chain. n Since the next slave node 3 is connected, a command is sent to change the state of switches 5 and 6 (step S16). Slave node 3 n Based on the command from master node 2, the termination switch 5 is turned OFF and the bus switch 6 is turned ON (step S17). As a result, slave node 3 n The termination state is released, and the next slave node 3 n+1 This enables communication with the other party.

[0028] Next, master node 2 scans for IDn+1 (specifically, it sends the question "Is this IDn+1?") (step S18). In response, slave node 3 n+1 When a response is received from (step S19), master node 2 will send a message to slave node 3 n+1 Register it as position number n+1 (step S20). Added slave node 3 n+1The switches 5 and 6 are in the initial state (the terminal switch 5 is ON and the bus switch 6 is OFF), that is, in the terminal state. Therefore, the additional registration of the slave node 3 n+1 is completed, and the terminal processing of the circuit 1 is also completed.

[0029] Figure 4 is a flowchart showing the operation monitoring procedure in the serial communication bus circuit 1. Here, in particular, the processing when a disconnection point of the circuit is detected by operation monitoring will be described.

[0030] At this stage, the registration of the position information for the slave nodes 31 to 3 p is completed. Therefore, the terminal switches 5 of the slave nodes 31 to 3 p are turned off, and the bus switches 6 are turned on (here, 1 < p ≦ n, and when p = n, the terminal switch 5 of the slave node 3 p is turned on, and the bus switch 6 is turned off).

[0031] The operation monitoring of the circuit can be performed by, for example, a keep-alive notification from the slave node 3 to the master node 2 or polling from the master node 2 to the slave node 3, but the means is not particularly limited. In Figure 4, the case where the operation of the circuit is monitored by a keep-alive notification from the slave node 3 to the master node 2 will be described as an example.

[0032] During operation, the master node 2 monitors the states of the slave nodes 31 to 3 n by periodically receiving keep-alive notifications from the slave nodes 31 to 3 n (step S21).

[0033] Here, as shown in Figure 4, when the keep-alive notifications from the slave nodes 31 to 3 p-1 arrive, but the keep-alive notification from the slave node 3 p does not arrive, the master node 2 will pIt is determined that there is a break in the connection between the master node and the slave node, and the circuit operation is updated (step S22). Specifically, the master node 2 determines that there is a break in the connection between the master node and the slave node 3. p The slave node 3 immediately preceding (the one before) p-1 For the next slave node 3 p Since it is disconnected, a command is sent to change the state of switches 5 and 6 (step S23). Slave node 3 p-1 Based on the command from master node 2, the termination switch 5 is turned ON and the bus switch 6 is turned OFF (step S24). As a result, slave node 3 p-1 Since switches 5 and 6 are in the termination state, circuit 1 is connected to master node 2 and slave nodes 31-3 p-1 The circuit will be updated to operate between the two points, restoring communication in that section and preventing a situation where the entire circuit goes down and becomes unusable.

[0034] As explained above, according to the serial communication bus circuit 1 of this embodiment, multiple slave nodes 31-3 are connected to the master node 2. n Because it is a serial communication bus circuit that connects serially, it is possible to communicate with a small number of wires. Moreover, each slave node 31-3 n The circuit includes a termination resistor 4, a termination switch 5, and a bus switch 6. Initially, it is set to a terminated state (i.e., termination switch 5 is ON and bus switch 6 is OFF), and when it is determined that the next slave node 3 is connected to the slave node 3, the termination state is released (i.e., termination switch 5 is turned OFF and bus switch 6 is turned ON) based on a command from the master node 2. n+1 Even when the bus is expanded by adding this, it is still possible to automatically terminate circuit 1.

[0035] Furthermore, if communication from any of the slave nodes 3 is interrupted, the master node 2 will, based on its command, initiate communication with the disconnected slave node 3. p Slave node 3 immediately before p-1The bus switch is set to the terminated state (i.e., the termination switch 5 is ON and the bus switch 6 is OFF). Therefore, in conventional CAN bus circuits 101 where each node is connected to the main bus B, if the main bus B is disconnected midway, the termination resistor 4 is lost, which can cause data misrecognition and other problems, making the entire circuit 101 unstable or causing it to shut down and become unusable. In contrast, in the serial communication bus circuit 1 according to this embodiment, even if the bus B is disconnected midway, the intermediate path (slave node 3) remains accessible. p-1 Communication can be automatically restored up to that point.

[0036] Although embodiments of this invention have been described above, the specific configuration is not limited to the embodiments described above, and any design changes, etc., that do not depart from the gist of this invention are also included. For example, in the embodiments described above, the case in which each node is a control device mounted on a ship was described, but it may also be a control device mounted on a mobile body other than a ship (for example, a vehicle, aircraft, submarine, etc.).

[0037] 1. Serial communication bus circuit 2 Master Nodes 3 slave nodes 4 Termination resistors 5 Termination switch 6 Bus Switch B Bus

Claims

1. This is a serial communication bus circuit for sequentially connecting multiple slave nodes to a single master node. The slave node is equipped with a termination resistor, a termination switch for connecting and disconnecting the termination resistor to the bus, and a bus switch for connecting and disconnecting communication from the slave node to the next slave node, and in the initial state, the termination switch is connected and the bus switch is disconnected. Based on a command from the master node, the slave node disconnects the termination switch and connects the bus switch when the next slave node is connected to it. A serial communication bus circuit characterized by the following features.

2. If communication from any of the slave nodes is interrupted, the slave node immediately preceding the disconnected slave node will connect the termination switch and disconnect the bus switch, based on a command from the master node. The serial communication bus circuit according to feature 1.

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