JP2014239276A - Unidirectional communication system and method - Google Patents

Abstract

A collision of data transmitted from each transmitter to a communication bus with a simple configuration is avoided. A state information input terminal TA connected to a state information output terminal TB of a previous transmitter having a transmission order immediately before the own device is connected to each transmitter 10 and one from the own device. A status information input terminal TA of a transmitter immediately after having a later transmission order and a status information output terminal TB wired in a one-to-one relationship are provided, and the status information management unit 13 immediately before receiving it via the status information input terminal TA Based on the state information of the transmitter, when it is confirmed that the immediately preceding transmitter has transitioned from the data transmitting state to the data non-transmitting state, the transmission processing unit 14 transmits its own device to the receiver via the communication bus B. Data transmission is started and data is not transmitted from the data transmitting state by outputting the status information of the own device from the status information output terminal TB to the transmitter immediately after the data transmission is started. The transition to the state It is notified before the transmitter. [Selection] Figure 1

Description

  The present invention relates to a unidirectional communication technique in which each of a plurality of transmitters sequentially transmits data to a single receiver via a common communication bus according to a predetermined transmission order.

  In a unidirectional communication system in which data communication from a transmitter to a receiver is unidirectional (one direction), a plurality of transmitters may be required for one receiver. For example, when complex calculations or multiple calculations are required, or when measurement locations are discrete, the data obtained by each transmitter is transmitted to a single receiver, and the receiver that receives these data A predetermined calculation is performed.

  In such a unidirectional communication system, if a plurality of transmitters are connected by providing a common communication bus and data is transmitted from each transmitter at an arbitrary timing, data may collide on the communication bus. There is. For this reason, correct data cannot be received by the receiver, causing a communication error, equipment failure, and system malfunction. In addition, if it is allowed to change the communication method bidirectionally or to provide a communication bus for each transmitter individually, such problems will not occur, but the scale of equipment such as the communication bus, transmitter, receiver, etc. Equipment costs will increase.

  Conventionally, as a technique related to such a unidirectional communication system, a technique using an AC power line as a communication path has been proposed (see, for example, Patent Document 1). In this technology, in a unidirectional communication in which signals are transmitted from a plurality of transmitters to a single receiver in a single direction, each transmitter receives a signal periodically by a timer synchronized with the voltage of the AC power line. When a power failure occurs on the AC power line, the timer is switched to the operation by the internal oscillation circuit, and when the signal is transmitted, the state of the timer is added to the signal and transmitted.

JP-A-11-284551

  However, in such a prior art, since the transmission timing of each transmitter is determined based on the voltage change of the AC power line, when using a communication path other than the AC power line, an internal oscillation circuit is provided in each transmitter. Therefore, it is necessary to determine the transmission timing of each transmitter. In addition to this, a circuit configuration for determining the transmission timing of each transmitter based on the voltage change of the AC power line, such as a power supply synchronous pulse circuit and a power failure detection circuit, is required. For this reason, there has been a problem that the circuit configuration of the transmitter is complicated, and the equipment scale and equipment cost of the entire system are increased.

  The present invention is for solving such problems, and an object of the present invention is to provide a unidirectional communication technique capable of avoiding a collision of data transmitted from each transmitter to a common communication bus with a simple configuration. Yes.

  In order to achieve such an object, in the unidirectional communication system according to the present invention, each of a plurality of transmitters is sequentially transmitted to a single receiver via a common communication bus according to a predetermined transmission order. A unidirectional communication system for transmitting data, wherein each of the transmitters has a state information input wired in a one-to-one relationship with a state information output terminal of a previous transmitter having a transmission order one prior to the own device. A status information input terminal connected in a one-to-one relationship with a status information input terminal of a transmitter immediately after having a transmission order one after the terminal, and the immediately preceding transmitter received via the status information input terminal Based on the state information, when it is confirmed that the immediately preceding transmitter has transitioned from the data transmitting state to the data non-transmitting state, transmission of own data to the receiver via the communication bus is started, The aircraft In response to the end of data transmission, the status information output terminal outputs the status information of the own device to the immediately subsequent transmitter, thereby notifying that the own device has transitioned from the data transmitting state to the data non-transmitting state. And a transmission processing unit.

  In addition, in one configuration example of the unidirectional communication system according to the present invention, the transmission processing unit is connected to the transmitter immediately after the status information output terminal in parallel with the transmission of the own data. Notifying the transmitting state information indicating that it is in a data transmitting state, and according to the end of transmission of the own device data, the own device is in a data non-transmitting state from the state information output terminal to the immediately following transmitter. The non-transmission state information indicating is notified.

  Also, in one configuration example of the unidirectional communication system according to the present invention, the transmission processing unit is configured so that the own device transfers from the status information output terminal to the immediately subsequent transmitter in response to the end of transmission of the own device data. Transition state information indicating a transition from a data transmission state to a data non-transmission state is notified.

  The unidirectional communication method according to the present invention is a unidirectional communication system in which each of a plurality of transmitters sequentially transmits data to a single receiver via a common communication bus in accordance with a predetermined transmission order. Is a unidirectional communication method used in the above, and based on the status information of the immediately preceding transmitter received from the immediately preceding transmitter having the transmission order one before the own device, the immediately preceding transmitter is in a data transmitting state. The immediately preceding transmitter transmission state confirmation step for confirming the transition to the data non-transmission state, and at the time when it is confirmed that the previous transmitter has transitioned from the data transmitting state to the data non-transmission state, via the communication bus The own data transmission step for starting transmission of own data to the receiver, and the transmission of the own data to the immediately subsequent transmitter having the next transmission order after the own data in response to the end of transmission of the own data By outputting the status information, and a ship transmitting state notification step of notifying that the own apparatus has transited from the data transmission state to a data non-transmission state.

  According to the present invention, each transmitter starts transmission of its own data after confirming the end of data transmission at the immediately preceding transmitter based on the status information of the immediately preceding transmitter notified from the immediately preceding transmitter. Can do. Therefore, compared with the case of determining the transmission timing of each transmitter based on the voltage change of the AC power line, with a very simple configuration that detects the change in the status information of the transmitter immediately before being input to the status information input terminal, It becomes possible to avoid collision of data transmitted from each transmitter to a common communication bus. For this reason, it becomes possible to significantly reduce the equipment scale and equipment cost of the entire unidirectional communication system.

It is a block diagram which shows the structure of the unidirectional communication system concerning 1st Embodiment. It is a flowchart which shows the data transmission process of the unidirectional communication system concerning a 1st form. It is a timing chart which shows the data transmission operation | movement of the unidirectional communication system concerning a 1st form. It is a flowchart which shows the data transmission process of the unidirectional communication system concerning a 2nd form. It is a timing chart which shows the data transmission operation | movement of the unidirectional communication system concerning a 2nd form.

Next, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
First, a unidirectional communication system 1 according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of a unidirectional communication system according to a first embodiment.

  In this unidirectional communication system 1, each of a plurality of transmitters 10 (10 (1) to 10 (N)) is transmitted to a single receiver 20 via a common communication bus B in accordance with a predetermined transmission order. The communication system sequentially transmits data. Here, the transmitter 10 (1), transmitter 10 (2),..., Transmitter 10 (N-1), transmitter 10 (N), transmitter 10 (1),. A case where data is transmitted to the communication bus B will be described as an example.

  Each of the transmitters 10 includes a state information input terminal TA, a state information output terminal TB, a transmission data generation unit 11, a communication I / F unit 12, a state information management unit 13, and a transmission processing unit 14 as main functional units. Is provided.

The state information input terminal TA is an input terminal connected in a one-to-one relationship with the state information output terminal of the immediately preceding transmitter having the transmission order one before the own device through the inter-transmitter control line L.
The status information output terminal TB is an output terminal connected in a one-to-one relationship with the status information input terminal of the immediately following transmitter having the next transmission order from the own device via the inter-transmitter control line L.

The transmission data generation unit 11 processes data acquired from various sensors mounted on the own device and external devices connected to the own device, and generates and transmits the data as own device data to be transmitted to the receiver 20. It has a function of outputting to the processing unit 14.
The communication I / F unit 12 has a function of transmitting own device data to the receiver 20 via the communication bus B in response to an instruction from the transmission processing unit 14.

  The status information management unit 13 has a function of acquiring status information indicating the transmission status of the previous transmitter from the previous transmitter via the inter-transmitter control line L and the status information input terminal TA, and outputting the status information to the transmission processing unit 14. In response to an instruction from the transmission processing unit 14, it has a function of notifying the transmitter immediately after the status information output terminal TB and the inter-transmitter control line L of the status information indicating its own transmission status. Yes.

  The transmission processing unit 14 confirms that the previous transmitter has transitioned from the data transmitting state to the data non-transmitting state based on the state information of the immediately previous transmitter acquired by the state information management unit 13. A function for instructing the F unit 12 to transmit the own device data to the receiver 20 and outputting the status information of the own device to the immediately following transmitter to the status information managing unit 13 in response to the end of transmission of the own device data. Thus, it has a function of instructing that its own device transits from the data transmitting state to the data non-transmitting state.

  In the present embodiment, as a method of notifying the transmitter immediately after the transition from the data transmission state to the data non-transmission state, the own device is transmitting data in parallel with the transmission of the own device data. In-transmission status information indicating that the device itself is in a data non-transmission state in response to the end of transmission of the own device data Is.

  Therefore, as a specific function, the transmission processing unit 14 according to the present embodiment is in the middle of transmitting indicating that the own device is in the state of data transmission to the immediately following transmitter by an instruction to the state information management unit 13. Notifying the status information management unit 13 of the function for notifying the status information and the non-status information indicating that the own device is in the non-transmitting state to the immediately following transmitter according to the instruction to the status information management unit 13 It has the function to do.

[Operation of First Embodiment]
Next, with reference to FIG. 2 and FIG. 3, the data transmission operation of the unidirectional communication system 1 according to the present embodiment will be described. FIG. 2 is a flowchart showing data transmission processing of the unidirectional communication system according to the first embodiment. FIG. 3 is a timing chart showing a data transmission operation of the unidirectional communication system according to the first embodiment.

Each transmitter 10 (1) to 10 (N) executes the data transmission process of FIG. 2 in response to the activation of the unidirectional communication system 1.
Here, when notifying the state information between the transmitters 10 (1) to 10 (N) via the inter-transmitter control line L, the state information output terminal TB is set to the high level with respect to the inter-transmitter control line L. By outputting the potential, the transmission state information indicating the data transmission state of the own device is notified, and the low-level potential is output from the state information output terminal TB to the inter-transmitter control line L. A case where non-transmission state information indicating a data non-transmission state is notified will be described as an example.

First, the state information management unit 13 detects the state information of the immediately preceding transmitter notified from the immediately preceding transmitter by detecting the potential of the state information input terminal TA (step 100). Here, when the potential of the state information input terminal TA is at a low level, the state information management unit 13 determines that the immediately preceding transmitter is in a data non-transmission state, and the potential of the state information input terminal TA is at a high level. In this case, it is determined that the immediately preceding transmitter is in a data transmitting state.
Therefore, the state information management unit 13 changes its own transmission until the potential of the state information input terminal TA changes from the high level to the low level, that is, the previous transmitter changes from the data transmitting state to the data non-transmitting state. Until the timing arrives (step 101: NO), the process returns to step 100 repeatedly and waits.

  On the other hand, the state information management unit 13 confirms that the potential of the state information input terminal TA has changed from a high level to a low level, and the immediately preceding transmitter has changed from a data transmitting state to a data non-transmitting state. Is transmitted (step 101: YES), the transmission processing unit 14 instructs the state information management unit 13 to notify the transmitter immediately after transmission of the state information being transmitted. In response to this, the status information management unit 13 outputs a high-level potential from the status information output terminal TB to the inter-transmitter control line L, thereby indicating the transmitting status information indicating the own data transmitting status. Is immediately notified to the transmitter (step 102).

  Subsequently, the transmission processing unit 14 instructs the communication I / F unit 12 to transmit own device data to the receiver 20. In response to this, the communication I / F unit 12 starts transmitting its own data to the receiver 20 via the common communication bus B (step 103).

  Thereafter, the transmission processing unit 14 waits until the transmission of the own device data is completed (step 104: NO), and in response to the completion of the transmission of the own device data (step 104: YES), the transmission processing unit 14 The state information management unit 13 is instructed to notify the non-transmission state information. In response to this, the state information management unit 13 outputs a low-level potential to the inter-transmitter control line L from the state information output terminal TB, thereby indicating non-transmission state information indicating the data non-transmission state of the own device. Is immediately notified to the transmitter (step 105), and the process returns to step 100.

  Therefore, in the operation example of FIG. 3, first, when transmission of the own device data D (1) is started by the transmitter 10 (1) at time T1, the state information output terminal TB of the transmitter 10 (1) A high-level potential, that is, transmission status information is output. Thereafter, when the transmission of own data D (1) is completed at transmitter T (1) at time T2, a low-level potential, that is, non-transmission status information is output from status information output terminal TB of transmitter 10 (1). Is output.

  The transmitter 10 (2) corresponding to the transmitter immediately after the transmitter 10 (1) changes the state information input terminal TA from the high level potential to the low level potential at the time T2, and immediately before the transmitter 10 (2). It is confirmed that the transmitter 10 (1) corresponding to the transmitter has transitioned from the data transmitting state to the data non-transmitting state. As a result, the transmitter 10 (2) outputs a high-level potential, that is, in-transmission state information, from the state information output terminal TB, and starts transmission of its own data D (2) from the communication bus B to the receiver 20. .

Thereafter, when transmission of the own device data D (2) is completed at time T3, the transmitter 10 (2) outputs a low level potential, that is, non-transmission state information from the state information output terminal TB.
Thereby, the transmitter 10 (3) corresponding to the transmitter immediately after the transmitter 10 (2) changes the state information input terminal TA from the high level potential to the low level potential at the time T3, so that the transmitter 10 (3 ) Confirms that the transmitter 10 (2) corresponding to the immediately preceding transmitter has transitioned from the data transmitting state to the data non-transmitting state, and notifies the transmitter 20 of the state information and the own data to the receiver 20. Transmission of D (3) is started.

  Thereafter, the own device data is sequentially transmitted to the transmitters 10 (4) to 10 (N) in the same manner, and the transmission of the own device data D (N) from the transmitter 10 (N) is completed at time T11. The transmitter 10 (1) corresponding to the transmitter immediately after the transmitter 10 (N) starts notifying the status information of the own device to the immediately subsequent transmitter and transmitting the own device data D (1) to the receiver 20. Will do.

[Effect of the first embodiment]
As described above, in this embodiment, each transmitter 10 has a state information input terminal TA that is connected in a one-to-one relationship with the state information output terminal TB of the immediately preceding transmitter having the transmission order one before the own device. , A state information input terminal TA of a transmitter immediately after having a transmission order one after the own device and a state information output terminal TB wired in a one-to-one relationship are provided, and the state information management unit 13 includes a state information input terminal TA. The transmission processing unit 14 transmits the data of its own device when it is confirmed that the previous transmitter has transitioned from the data transmitting state to the data non-transmitting state based on the status information of the immediately preceding transmitter received via Instructing the communication I / F unit 12 and receiving it, the communication I / F unit 12 starts transmitting its own data to the receiver 20 via the communication bus B, and in response to the end of transmission of the own device data. Status information output via status information management unit 13 By outputting the state information of its own to the right after the transmitter from the child TB, in which the own apparatus has to notify immediately before the transmitter that it has transitioned from the data transmission state to a data non-transmission state.

  Thus, each transmitter 10 can start transmitting its own data after confirming the end of data transmission at the immediately preceding transmitter based on the status information of the immediately preceding transmitter notified from the immediately preceding transmitter. . Therefore, compared with the case where the transmission timing of each transmitter is determined based on the voltage change of the AC power line as described above, the change of the state information from the immediately preceding transmitter input to the state information input terminal TA is detected. With an extremely simple configuration, it is possible to avoid collision of data transmitted from each transmitter 10 to the common communication bus B. For this reason, it becomes possible to significantly reduce the equipment scale and equipment cost of the entire unidirectional communication system.

  Further, according to the present embodiment, the transmission processing unit 14 outputs the state information via the state information management unit 13 in parallel with the transmission of the own device data in response to the confirmation of the arrival of the transmission timing by the state information management unit 13. Notifying the transmitter immediately after the terminal TB to the transmitting state information indicating that the own device is in a data transmitting state, and outputting the state information via the state information management unit 13 in response to the end of transmission of the own device data Non-transmission state information indicating that the own device is in a data non-transmission state is notified from the terminal TB to the transmitter immediately thereafter.

  Therefore, the transmission state of the transmitter, that is, the data transmission state and the data non-transmission state can be notified by binary information, and a potential composed of a high level and a low level can be used as the state information. Thereby, the configuration of the state information management unit 13 that inputs and outputs the state information can be an extremely simple circuit configuration. In addition, the immediately subsequent transmitter can also grasp the start of data transmission by the immediately preceding transmitter of its own device, for example, processing operation for generating new own device data in preparation for the arrival of its own transmission timing. Can be executed in advance, and the response performance of the entire unidirectional communication system can be improved.

[Second Embodiment]
Next, with reference to FIG. 4 and FIG. 5, the unidirectional communication system 1 concerning the 2nd Embodiment of this invention is demonstrated. FIG. 4 is a flowchart showing data transmission processing of the unidirectional communication system according to the second embodiment. FIG. 5 is a timing chart showing a data transmission operation of the unidirectional communication system according to the second embodiment.

  In the first embodiment, as a method for notifying the transmitter immediately after the transition from the data transmission state to the data non-transmission state, the own device is transmitting data in parallel with the transmission of the own device data. As an example, send the status information indicating the status to the transmitter immediately after, and notify the transmitter immediately after the transmission of the data of the own device that the non-transmission status information indicating that the device is in a data non-transmission status. explained.

In the present embodiment, in parallel with the transmission of the own device data, the transmission state information is not immediately notified to the transmitter, and the own device changes from the data transmission state to the data non-transmission state in response to the end of the transmission of the own device data. A case will be described as an example where transition state information indicating a transition is immediately notified to the transmitter.
That is, the transmission processing unit 14 according to the present embodiment is in a state where the own device is transmitting data from the state information output terminal TB to the immediately subsequent transmitter via the state information management unit 13 in response to the end of transmission of the own device data. Has a function of notifying transition state information indicating a transition from a data non-transmission state to a data non-transmission state. In addition, about the other structure in each transmitter 10, it is the same as that of 1st Embodiment, and description here is abbreviate | omitted.

[Operation of Second Embodiment]
Next, with reference to FIG. 4 and FIG. 5, the data transmission operation of the unidirectional communication system 1 according to the present embodiment will be described.
Each transmitter 10 (1) to 10 (N) executes the data transmission process of FIG. 4 in response to the activation of the unidirectional communication system 1.

  Here, when notifying the status information of the own device between the transmitters 10 (1) to 10 (N) via the inter-transmitter control line L, the status information output terminal TB is connected to the inter-transmitter control line L. An example will be described in which transition state information indicating a transition from a data transmission state to a data non-transmission state is notified by outputting a pulse signal.

  First, the state information management unit 13 detects the potential of the state information input terminal TA, confirms the presence / absence of notification of transition state information using a pulse signal from the immediately preceding transmitter (step 200), and sends it to the state information input terminal TA. Until the pulse signal is input, that is, until the previous transmitter changes from the data transmitting state to the data non-transmitting state and the transmission timing of the own device arrives (step 201: NO), the processing returns to step 200 repeatedly.

  On the other hand, when a pulse signal is input to the state information input terminal TA, it is confirmed by the state information management unit 13 that the previous transmitter has transitioned from the data transmitting state to the data non-transmitting state, and the transmission timing of the own device has arrived. In the case (step 201: YES), the transmission processing unit 14 instructs the communication I / F unit 12 to transmit own data to the receiver 20. In response to this, the communication I / F unit 12 starts transmitting its own data to the receiver 20 via the common communication bus B (step 202).

  Thereafter, the transmission processing unit 14 waits until the transmission of the own device data is completed (step 203: NO), and in response to the completion of the transmission of the own device data (step 203: YES), the transmission processing unit 14 The state information management unit 13 is instructed to notify the non-transmission state information. In response to this, the state information management unit 13 outputs a low-level potential to the inter-transmitter control line L from the state information output terminal TB, thereby indicating non-transmission state information indicating the data non-transmission state of the own device. Is immediately notified to the transmitter (step 204), and the process returns to step 200.

  Therefore, in the operation example of FIG. 5, first, transmission of own data D (1) is started by transmitter 10 (1) at time T1, and then the own data D is transmitted by transmitter 10 (1) at time T2. When the transmission of (1) is completed, transition state information including a pulse signal is output from the state information output terminal TB of the transmitter 10 (1).

  The transmitter 10 (2) corresponding to the transmitter immediately after the transmitter 10 (1) is equivalent to the transmitter immediately before the transmitter 10 (2) when the pulse signal is input to the state information input terminal TA at time T2. It is confirmed that the transmitter 10 (1) to be transferred has transitioned from the data transmitting state to the data non-transmitting state. Thereby, the transmitter 10 (2) starts transmission of its own data D (2) from the communication bus B to the receiver 20.

Thereafter, when transmission of the own data D (2) is completed at time T3, the transmitter 10 (2) outputs transition state information including a pulse signal from the state information output terminal TB.
As a result, the transmitter 10 (3) corresponding to the transmitter immediately after the transmitter 10 (2) receives the pulse signal from the state information input terminal TA at time T3, and transmits immediately before the transmitter 10 (3). It is confirmed that the transmitter 10 (2) corresponding to the device has transitioned from the data transmitting state to the data non-transmitting state, and transmission of the own device data D (3) is started.

  Thereafter, the own device data is sequentially transmitted to the transmitters 10 (4) to 10 (N) in the same manner, and the transmission of the own device data D (N) from the transmitter 10 (N) is completed at time T11. Then, the transmitter 10 (1) corresponding to the transmitter immediately after the transmitter 10 (N) starts transmission of its own device data D (1) to the receiver 20.

[Effect of the second embodiment]
As described above, according to the present embodiment, the transmission processing unit 14 changes from the state information output terminal TB to the transmitter immediately after the transmission of the own device data, and the own device changes from the data transmitting state to the data non-transmitting state. Since the transition state information indicating the transition is notified, the transition from the transmitting state of the transmitter, that is, the data transmitting state to the data non-transmitting state is notified by information having a short signal transmission period such as a pulse signal. be able to. Thereby, the power required for notification of state information can be reduced, and the power consumption of the entire unidirectional communication system can be reduced.

[Extended embodiment]
The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a consistent range.

  DESCRIPTION OF SYMBOLS 1 ... Unidirectional communication system 10, 10 (1), 10 (2), 10 (3), 10 (N-1), 10 (N) ... Transmitter, 11 ... Transmission data generation part, 12 ... Communication I / F unit, 13 ... status information management unit, 14 ... transmission processing unit, 20 ... receiver, B ... communication bus, L ... inter-transmitter control line.

Claims (4)

A unidirectional communication system in which each of a plurality of transmitters sequentially transmits data according to a predetermined transmission order to a single receiver via a common communication bus,
Each of the transmitters is
A status information input terminal connected in a one-to-one relationship with the status information output terminal of the immediately preceding transmitter having a transmission order one before the own machine;
A status information output terminal connected in a one-to-one relationship with the status information input terminal of the transmitter immediately after having the transmission order one after the own machine;
Based on the status information of the immediately preceding transmitter received via the status information input terminal, when it is confirmed that the immediately preceding transmitter has transitioned from the data transmitting state to the data non-transmitting state, the communication bus The own device starts transmitting its own data to the receiver, and outputs the status information of the own device from the status information output terminal to the transmitter immediately after the transmission of the own device data. A unidirectional communication system comprising: a transmission processing unit that notifies that a transition from a data transmission state to a data non-transmission state is made. The unidirectional communication system according to claim 1, wherein
In parallel with the transmission of the own device data, the transmission processing unit notifies the transmitting state information indicating that the own device is in a data transmitting state from the state information output terminal to the immediately following transmitter, and Unidirectional communication characterized in that, in response to the end of transmission of own device data, non-transmission state information indicating that the own device is in a data non-transmission state is notified from the state information output terminal to the immediately following transmitter. system. The unidirectional communication system according to claim 1, wherein
The transmission processing unit indicates transition state information indicating that the own device has transitioned from a data transmitting state to a data non-transmitting state from the state information output terminal to the immediately subsequent transmitter in response to the end of transmission of the own device data. A unidirectional communication system, characterized by: A unidirectional communication method used in a unidirectional communication system in which each of a plurality of transmitters sequentially transmits data to a single receiver via a common communication bus according to a predetermined transmission order,
Immediately before confirming that the immediately preceding transmitter has transitioned from the data transmitting state to the data non-transmitting state based on the state information of the immediately preceding transmitter received from the immediately preceding transmitter having the previous transmission order from the own device Transmitter transmission status confirmation step,
When it is confirmed that the immediately preceding transmitter has transitioned from a data transmitting state to a data non-transmitting state, own data transmission step for starting transmission of own data to the receiver via the communication bus;
In response to the end of transmission of the own device data, by outputting the status information of the own device to the transmitter immediately after having the transmission order one after the own device, the own device changes from the data transmitting state to the data non-transmitting state. A unidirectional communication method comprising: a transmission state notifying step for notifying that a transition has occurred.

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