JP3783960B2 - Data transmission method, data transmission system, and data transmission apparatus - Google Patents

Description

  The present invention relates to a data transmission method, a data transmission system, and a data transmission device, and more specifically, a data transmission method between data transmission devices connected by a transmission line in a ring type or the like, its data transmission system, And a data transmission apparatus.

  2. Description of the Related Art In recent years, when the Internet and image information such as car navigation and ITS (Intelligent Transport Systems) are transmitted in a space such as an automobile, large-capacity and high-speed communication is required. Communication systems for transmitting digital data such as digitized video and audio data, or computer data are being actively studied, and a network that transmits digital data even in spaces such as automobiles has been fully introduced. It is becoming. In this in-vehicle network, for example, a physical topology is a ring topology, and a plurality of nodes are connected by a ring topology to form a one-way ring LAN, and audio equipment, navigation equipment, information terminal equipment, or Aiming for an integrated connection to security devices. As an information communication protocol used in the ring LAN, there is, for example, Media Oriented Systems Transport (hereinafter referred to as MOST). In this MOST, not only a communication protocol but also a method for constructing a distributed system is mentioned, and data of the MOST network is transmitted with a frame as a basic unit, and the frame is transmitted in one direction to each node one after another.

  By the way, in the case of a ring-type LAN provided in a car or the like, radiation noise may cause malfunction of other electronic devices mounted on the car or the like, and may be affected by radiation noise from other devices. There is also a need for accurate transmission. For this reason, in a conventional ring LAN using MOST, each node is connected by an optical fiber cable and optically communicates with each other, thereby improving noise resistance while preventing generation of electromagnetic waves. On the other hand, there is also a data transmission system that performs electrical communication using an inexpensive cable such as a twisted pair cable or a coaxial cable, and enables high-speed data transmission exceeding 20 Mbps while improving noise resistance with less radiation noise. Yes (see, for example, Patent Document 1).

  A conventional data transmission system using telecommunications will be described with reference to FIG. FIG. 6 is a block diagram showing the configuration of the data transmission system.

  In FIG. 6, the data transmission system includes n-stage data transmission apparatuses 101a to 101n in which each node transmits and receives data. Each of the data transmission apparatuses 101a to 101n is connected in a ring shape via a transmission line 110 constituted by a coaxial cable or a twisted pair wire. Each of the data transmission apparatuses 101a to 101n is connected to connection devices 100a to 100n, respectively. The connection apparatuses 100a to 100n are based on data output from the data transmission apparatuses 101a to 101n to which the connection devices 100a to 100n are connected, respectively. The processing is performed and the result is output to the data transmission apparatuses 101a to 101n. Here, the data transmission apparatus 101a is a master that transmits data using its own clock, and the other data transmission apparatuses 101b to 101n establish clock synchronization using a lock signal for establishing clock synchronization received from the master. It is a slave to do. Each of the data transmission apparatuses 101a to 101n has substantially the same configuration, but as a representative of them, first, the configuration of the master data transmission apparatus 101a and the flow of transmission / reception data will be described.

  The data transmission apparatus 101a includes a transmission / reception unit (physical layer) 102a, a MOST controller (link layer) 103a, and a CPU 104a. The transmitting / receiving unit 102a includes a receiving unit 121a and a transmitting unit 122a.

  The data transmission apparatus 101a outputs data to the data transmission apparatus 101b via the transmission path 110, and receives data from the data transmission apparatus 101n. Data from the connected device 100a connected to the data transmission apparatus 101a is processed by the MOST controller 103a and output as a digital data string. Then, the digital data sequence is collectively made into data symbols for each predetermined bit by the transmission unit 122a, and mapping and filtering processing by the conversion table is performed. The digital signal processed by the transmission unit 122 a is converted into an analog signal and output to the transmission path 110. The analog signal is output as a waveform having a predetermined period in which the digital data string is mapped to one of a plurality of signal levels. On the other hand, the receiving unit 121a of the data transmission apparatus 101a receives the analog signal output from the data transmission apparatus 101n via the transmission path 110 and converts it into a digital signal. Then, the receiving unit 121a decodes the digital signal into data symbols through filtering processing and inverse mapping, converts the digital signal into a digital data string, and outputs the digital data string to the MOST controller 103a.

  In the data transmission system configured as described above, initialization processing is performed on the MOST controllers 103a to 103n as the link layer of the protocol and the transmission / reception units 102a to 102n as the physical layer in order to define the mechanical connection. During the initialization operation, the clock synchronization of each of the data transmission apparatuses 101a to 101n is established and a determination level that is a reference for data determination is set. The initialization process in the data transmission system will be described below with reference to FIGS. FIG. 7 is a sequence diagram showing an initialization process of the data transmission apparatuses 101a to 101n in the data transmission system.

  In the data transmission system, the MOST controllers 103a to 103n that are the link layers of the data transmission apparatuses 101a to 101n and the transmission / reception units 102a to 102n that are the physical layers are all in a reset state before the initialization operation. First, the CPUs 104a to 104n of the data transmission apparatuses 101a to 101n cancel the reset state of the transmission / reception units 102a to 102n, respectively, when the system is turned on. Then, the transmission / reception unit 102a cancels the reset state and performs initialization processing of itself (physical layer). In this initialization process, the initialization process is performed including the transmission / reception units 102b to 102n, which are other physical layers of the protocol, in order to define the mechanical connection.

  First, the master transmission / reception unit 102a transmits a lock signal to the transmission line 110 based on an output frequency using the resonator of the own device as a reference frequency. This lock signal is, for example, a sine wave signal based on the clock frequency of the master data transmission apparatus 101a.

  On the other hand, the slave transmission / reception unit 102b receives the lock signal from the transmission line 110, performs clock recovery, and sets a reception PLL. Then, the transmission / reception unit 102b transmits a lock signal to the transmission line 110 based on the reproduction clock of the reception PLL. Each of the other slave transmission / reception units 102c to 102n also receives the lock signal sent from the data transmission device upstream of its own device, regenerates the clock, sets the reception PLL, and then regenerates the received PLL. Based on the above, a lock signal is transmitted to the downstream data transmission apparatus. Then, the master transmission / reception unit 102a receives the lock signal transmitted from the upstream transmission / reception unit 102n, performs clock recovery, and sets a reception PLL.

  Next, the master transmission / reception unit 102 a generates a training signal for setting a determination level as a data determination reference with the slave transmission / reception unit 102 b arranged downstream, and transmits the training signal to the transmission path 110. To do. The training signal includes, for example, a clock reproduction sine wave in which the maximum and minimum amplitude levels appear alternately, a training pattern header (for example, the maximum or minimum amplitude level continues for a predetermined period), and each data transmission apparatus 101. And a training pattern which is a known data pattern. As the training pattern, a PN pattern signal or the like in which all the data symbol values are included and various patterns appear is used.

  The slave transmitting / receiving unit 102 b receives the training signal from the transmission path 110, immediately generates a training signal with the downstream data transmission apparatus 101 c, and transmits the training signal to the transmission path 110. Then, the transmission / reception unit 102b uses the received training signal in the reception unit 121b of its own apparatus to set a determination level for determining a transmission level threshold value for each symbol value. Each judgment value with the judgment level as a boundary is set. The other slave transmission / reception units 102c to 102n also receive the training signal transmitted from the upstream data transmission apparatus 101, and immediately transmit the training signal of the own apparatus to the downstream data transmission apparatus 101. Similarly, in the other slave transmission / reception units 102c to 102n, the reception units 121c to 121n respectively determine the transmission level threshold value for each symbol value using the training signal received from the upstream data transmission apparatus 101. Each determination level is set to set the determination level, and a determination value with the determination level as a boundary is set. The master transmission / reception unit 102a also uses the training signal received from the transmission / reception unit 102n to set a determination level for determining a transmission level threshold value for each symbol value, and determines the determination level and the determination level. Set each judgment value with as the boundary. As a result, the physical layer initialization process of the data transmission system is completed, and the respective physical layers become ready for data communication with each other.

  After the physical layer initialization process of the entire system is completed, the CPUs 104a to 104n release the reset states of the MOST controllers 103a to 103n, respectively. Then, the MOST controllers 103a to 103n release the reset state, start an operation based on a predetermined reference frequency, and start an initialization process of itself (link layer).

  In the link layer initialization processing, synchronization is established between the link layer and the physical layer of the device itself, and frame synchronization is established between the master link layer and the slave link layer. The master MOST controller 103a Check the overall network establishment. First, the master MOST controller 103a (link layer) outputs initialization data for performing initialization processing such as frame synchronization with other link layers to the transmission unit 122a. Using this initialization data, synchronization between the MOST controller 103a and the transmission unit 122a is established, and the PLL included in the MOST controller 103a is locked. Then, the initialization data is output from the transmission unit 122a to the transmission path 110.

  The slave receiver 121b receives the initialization data from the transmission line 110 and outputs it to the MOST controller 103b. Then, the MOST controller 103b establishes frame synchronization with the master MOST controller 103a using the input initialization data, and outputs the initialization data to the transmission unit 122b. Using this initialization data, synchronization between the MOST controller 103b and the transmission unit 122b is established, and the PLL included in the MOST controller 103b is locked. Then, the initialization data is output from the transmission unit 122b to the transmission line 110. The initialization data received by the reception unit 121b is output from the transmission unit 122b, bypassing the MOST controller 103b, until the PLL included in the MOST controller 103b is locked. Then, after the synchronization between the MOST controller 103b and the transmission unit 122b is established, all the data received by the reception unit 121b is output to the MOST controller 103b.

The other slave MOST controllers 103c to 103n also establish frame synchronization with the master MOST controller 103a using the input initialization data in the same manner, and output the initialization data to the transmission units 122c to 122n, respectively. To do. Then, the master MOST controller 103a receives the initialization data through the transmission / reception unit 102a (physical layer) a predetermined number of times, thereby confirming that the network has been established, and sends the establishment confirmation result to another link layer. To complete the link layer initialization process. After such initialization processing of the physical layer and the link layer, the respective data transmission apparatuses 101a to 101n start data communication with each other.
International Publication No. 02/30079 Pamphlet

  However, after the physical layer and the link layer described above are initialized, the conventional data transmission system transmits all data via each MOST controller. That is, the transmission / reception units (physical layers) 102a to 102n, the MOST controllers (link layers) 103a to 103n, and the CPUs (control units) 104a to 104n included in the data transmission apparatuses 101a to 101n are all maintained in an operable state. This increases the power consumption of the entire data transmission system. In general, when the MOST controllers 103a to 103n are maintained in an operable state, the connected devices 100a to 100n are similarly turned on, and thus the power consumption is further increased.

  On the other hand, in an automobile, a storage battery (battery) is generally used as a power source, and electric power generated by a generator (alternator) provided in the engine is stored during engine startup. When the engine is stopped, only the storage battery serves as a power source in the automobile, and there is a limit to the amount of power that can be used. Therefore, when the above-described data transmission system is installed in an automobile, this storage battery operates as a power source. Therefore, particularly when the data transmission system is used while the engine is stopped, power consumption must be suppressed as much as possible. However, even when, for example, a surveillance camera, a security system, or the like is configured as a part of the connection device of the data transmission system and only the part of the connection device is to be operated while the engine is stopped, Since it is necessary to keep all irrelevant hardware operable, power consumption is greatly increased.

  Therefore, an object of the present invention is to provide a data transmission method, a data transmission system, and a data transmission device that reduce power consumption of the entire system when operating only some of the connected devices connected to the data transmission system. It is to be.

  In order to achieve the above object, the present invention employs the following configuration. Note that reference numerals and the like in parentheses indicate correspondence with embodiments described later to help understanding of the present invention, and do not limit the scope of the present invention.

The data transmission system of the present invention includes a plurality of data transmission devices (1a to 1n) connected in a ring shape via a transmission line (11) , and each data transmission device transmits and receives transmission signals to and from each other. Each data transmission apparatus includes a processing unit (MOST controller 3) , a transmission / reception unit (2) , and a control unit (CPU 4) . The processing unit processes transmission / reception data (reception digital data string RX, transmission digital data string TX) based on a predetermined communication protocol. The transmission / reception unit generates a transmission signal based on the transmission data processed by the processing unit, outputs the transmission signal to the subsequent data transmission device, and generates reception data based on the transmission signal output from the previous data transmission device. Output to the processing unit. The control unit controls operations of the processing unit and the transmission / reception unit. The control units are communicably connected via a transmission line (12). Each of the first data transmission apparatuses, which is at least one of the plurality of data transmission apparatuses, generates reception data in accordance with the transmission signal output from the preceding data transmission apparatus in the transmission / reception unit, and then receives the reception data (bypass A transmission signal is generated in accordance with the digital data string BX) and output to the subsequent data transmission apparatus. Among the plurality of data transmission apparatuses, each of the second data transmission apparatuses different from the first data transmission apparatus processes received data generated according to the transmission signal output from the preceding data transmission apparatus in the transmission / reception unit. The processing unit performs processing based on the communication protocol, and the transmission / reception unit generates a transmission signal according to the transmission data processed based on the communication protocol by the processing unit, and outputs the transmission signal to the subsequent data transmission apparatus. The control unit included in the first data transmission device maintains the reset state in which the data processing operation of the processing unit of the own device is stopped based on the instruction input via the transmission line (instruction to prohibit reset release of the link layer) Control is performed (S77).

Each of the transmission / reception units may include a bypass route (a route between the determination processing unit 215 and the selector 221) and a selector (221). The bypass path bypasses the processing unit of its own device and outputs received data. The selector selects one of transmission data output from the processing unit and reception data output from the bypass path according to the operation state of the processing unit, and outputs the selected data to the transmission side (data mapping unit 222) of the transmission / reception unit. To do. In this case, as an example, the selector included in the first data transmission apparatus selects reception data output from the bypass path in accordance with an instruction from the outside of the transmission / reception unit of the own apparatus. As another example, the selector included in the first data transmission device is output from the bypass path when the processing unit of the own device is in a reset state in which the data processing operation is stopped (when the synchronization detection signal CS is not input). Select received data .

  Each of the transmission / reception units may include a data mapping unit (222) and a determination processing unit (215). The data mapping unit maps each symbol of transmission data to one of a plurality of signal levels to generate a transmission signal. The determination processing unit generates reception data based on a determination level for distinguishing and determining a plurality of signal levels of the transmission signal.

  The communication protocol used by the processing unit is specifically defined by MOST.

The data transmission device of the present invention is connected to another device via a transmission line in a ring shape, and transmits / receives transmission signals to / from the other device. The data transmission apparatus includes a processing unit , a transmission / reception unit , and a control unit . The processing unit processes transmission / reception data based on a predetermined communication protocol. The transmission / reception unit generates a transmission signal based on the transmission data processed by the processing unit and outputs the transmission signal to another device, and generates reception data based on the transmission signal output from the other device, and sends the transmission data to the processing unit. Output. The control unit controls operations of the processing unit and the transmission / reception unit. The control unit is communicably connected to the control unit of another device via a transmission line. In the first mode (bypass mode), the transmission / reception unit generates reception data according to a transmission signal output from another device, and then generates a transmission signal according to the reception data and outputs the transmission signal to the other device. To do. In a second mode (normal mode) different from the first mode, the transmission / reception unit outputs reception data generated according to a transmission signal output from another device to the processing unit, and the processing unit is a transmission / reception unit. Processes the received data output based on the communication protocol, outputs the transmission data processed based on the communication protocol to the transmission / reception unit, and the transmission / reception unit generates a transmission signal based on the transmission data output from the processing unit And output to other devices. The control unit performs control to maintain the reset state in which the data processing operation of the processing unit of the own apparatus is stopped based on the instruction indicating the first mode input via the transmission line.

The transmission / reception unit may include a bypass path and a selector. The bypass path bypasses the processing unit and outputs received data. The selector selects one of transmission data output from the processing unit and reception data output from the bypass path according to the operation state of the processing unit, and outputs the selected data to the transmission side of the transmission / reception unit. In this case, as an example, the selector selects reception data output from the bypass path in response to an instruction from the outside of the transmission / reception unit indicating the first mode. As another example, the selector selects received data output from the bypass path when the processing unit is in a reset state in which data processing operation is stopped in the first mode .

  Further, the transmission / reception unit may include a data mapping unit and a determination processing unit. The data mapping unit maps each symbol of transmission data to one of a plurality of signal levels to generate a transmission signal. The determination processing unit generates reception data based on a determination level for distinguishing and determining a plurality of signal levels of the transmission signal.

  The communication protocol used by the processing unit is specifically defined by MOST.

  According to the data transmission method of the present invention, the first data transmission apparatus that transmits data using only the physical layer of the own apparatus, and the second data transmission apparatus that transmits data using the link layer and the physical layer of the own apparatus. And are provided. Therefore, by setting a data transmission device that does not require link layer operation as the first data transmission device, the power consumption of the data transmission device can be reduced. For example, when only a specific connection device connected to each of a plurality of data transmission devices is operated, the data transmission device connected to a connection device that is not operated is operated as the first transmission device, thereby consuming the entire system. Electric power can be greatly reduced.

  In response to an instruction from the outside of the physical layer of the device, the first data transmission device needs to perform data processing in the link layer when received data bypasses the link layer of the device and transmits / receives a transmission signal. Therefore, power consumption at the link layer can be reduced.

  When the link layer of the first data transmission device is maintained in the reset state, the link layer does not perform data processing, so that the power consumption of the link layer can be reduced. In general, since the power supply to the connection device connected to the link layer in the reset state is also stopped, the power consumption of the connection device connected to the first data transmission apparatus can be greatly reduced. Further, when the link layer of the first device is in the reset state, the first data transmission device bypasses the link layer and transmits / receives transmission signals. Therefore, the first data transmission device can easily control the reset state of each link layer. In addition, data transmission bypassing the link layer can be performed. For example, since the control of the reset state in each link layer is performed in the initialization process for all the data transmission apparatuses, the data transmission apparatuses can cooperate with each other and shift to the respective modes.

  In addition, in the physical layer, a transmission signal is generated by mapping each symbol of transmission data to one of a plurality of signal levels, and a determination for distinguishing a plurality of signal levels of a transmission signal from received data is determined. In the case of generating based on the level, the first data transmission apparatus transmits / receives data to perform transmission processing by performing data transmission processing having mapping processing after data reception processing having data determination of the received transmission signal. Data transmission can be performed while reducing deterioration of data indicated by the transmission signal.

  More specifically, the communication protocol used in the data transmission method of the present invention is defined by MOST, and the same effect as described above can be obtained even when communication is performed using MOST as the communication protocol.

  Further, according to the data transmission system and the data transmission apparatus of the present invention, the same effect as the above-described data transmission method of the present invention can be obtained.

  A data transmission system according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of the data transmission system.

  In FIG. 1, the data transmission system forms a unidirectional ring LAN by connecting a plurality of nodes in a ring topology with a physical topology as a ring topology. Hereinafter, as an example of the data transmission system, each node is constituted by n stages of data transmission apparatuses 1a to 1n, each connected in a ring shape by a transmission line 11, and transmitted data is transmitted in one direction via the transmission line 11. A system to be transmitted will be described. Connected to each of the data transmission apparatuses 1a to 1n is a connection device 10a to 10n that performs processing based on the data transmitted through the data transmission system and outputs the result to the data transmission system. For example, the connection devices 10a to 10n are audio devices, navigation devices, information terminal devices, security devices, surveillance cameras, or the like. In addition, as a form of general hardware, each data transmission apparatus 1a-1n and each connection apparatus 10a-10n are each comprised integrally.

  As an information communication protocol used in the data transmission system, for example, there is Media Oriented Systems Transport (hereinafter referred to as MOST). Data transmitted using the MOST as a communication protocol is transmitted using a frame as a basic unit, and the frames are sequentially transmitted in one direction between the data transmission apparatuses 1a to 1n. That is, the data transmission device 1a outputs data to the data transmission device 1b via the transmission path 11. Further, the data transmission device 1b outputs data to the data transmission device 1c via the transmission line 11, and the data transmission device 1 (n-1) transmits to the data transmission device 1n via the transmission line 11. Output data. Then, the data transmission device 1n outputs data to the data transmission device 1a via the transmission path 11. An inexpensive cable such as a twisted pair wire or a coaxial cable is used for the transmission line 11, and the data transmission apparatuses 1 a to 1 n perform electrical communication with each other. Here, in the data transmission system, the data transmission device 1a is a master that transmits data using its own clock, and the other data transmission devices 1b to 1n are slaves that lock the frequency to the clock generated by the master. is there.

  Next, the configuration of the data transmission devices 1a to 1n will be described. Each of the data transmission apparatuses 1a to 1n has substantially the same configuration, but as a representative thereof, first, the schematic configuration of the master data transmission apparatus 1a and the flow of transmission / reception data will be described.

  The data transmission device 1a includes a transmission / reception unit (physical layer) 2a, a MOST controller (link layer) 3a, and a CPU (central processing unit: microcomputer) 4a. And the transmission / reception part 2a has the receiving part 21a and the transmission part 22a.

  For example, the MOST controller 3a is composed of an LSI, and a MOST controller chip or the like in which a communication protocol used in the data transmission system is defined is used. The MOST controller 3a is connected to a connection device 10a that performs processing based on data output from the MOST controller 3a and outputs the result to the MOST controller 3a. As one of the functions, the MOST controller 3a converts data from the connected device 10a into a protocol defined by MOST and outputs a digital data string to the transmission unit 22a of the transmission / reception unit 2a. Further, the MOST controller 3a receives the digital data string output from the receiving unit 21a and transmits it to the connected device 10a.

  The CPU 4a controls the MOST controller 3a and the transmission / reception unit 2a included in the data transmission device 1a. For example, the CPU 4a controls a reset function, power control, master / slave selection processing, transition processing to a diagnosis mode, and the like of the data transmission device 1a. The CPU 4a is serially connected to the CPUs 4b to 4n of the other data transmission apparatuses 1b to 1n via the transmission line 12 different from the transmission line 11, and selects a bypass mode to be described later for the other CPUs 4b to 4n. Instruct processing. In addition, you may provide CPU which controls the bypass mode of a data transmission system separately from CPU4a-4n which data transmission apparatus 1a-1n has. In this case, a separately provided CPU and CPUs 4 a to 4 n are serially connected via the transmission line 12.

  The transmission / reception unit 2a is typically composed of an LSI. From the MOST controller 3a, the digital data string is output to the transmission unit 22a as described above. The transmission unit 22a collects the digital data sequence for each predetermined bit into a data symbol, and performs mapping and filtering processing using a conversion table. Then, the transmitter 22a converts the mapped and filtered signal into an analog signal, amplifies the analog signal, converts it into a differential signal, and sends it to the transmission line 11. That is, the digital signal mapped and filtered by the transmission unit 22a is output as an analog waveform having a predetermined period in which the digital data string is mapped to one of a plurality of signal levels. The detailed configuration and operation of the transmission unit 22a will be described later.

  On the other hand, the receiving unit 21a receives the analog signal output from the data transmission device 1n via the transmission path 11, and converts it into a digital signal. The receiving unit 21a decodes the digital signal into data symbols through filtering and inverse mapping processing, converts the digital signal into a digital data string, and outputs the digital data string to the MOST controller 3a. The detailed configuration and operation of the receiving unit 21a will be described later.

  The configuration of the slave data transmission devices 1b to 1n is the same as that of the master data transmission device 1a. In the following description, the constituent parts of the slave data transmission apparatuses 1b to 1n are denoted by “b” to “n” in place of the reference symbol “a” given to the constituent parts of the master data transmission apparatus 1a. To explain. Further, when the data transmission devices 1a to 1n and their constituent parts are described generically, the reference numerals “a” to “n” given as the data transmission device 1 and given to the respective constituent units are omitted. Do.

  Next, a detailed configuration of the data transmission apparatus 1 will be described with reference to FIG. FIG. 2 is a block diagram showing the configuration of the data transmission apparatus 1.

  2, the data transmission device 1 includes the transmission / reception unit 2 having the reception unit 21 and the transmission unit 22, the MOST controller 3, and the CPU 4 as described above. The receiving unit 21 includes a differential receiver 211, a low-pass filter 212, an A / D converter 213, a digital filter 214, a determination processing unit 215, and a synchronization detection unit 216. The transmission unit 22 includes a selector 221, a data mapping unit 222, a digital filter 223, a D / A converter 224, a low-pass filter 225, a differential driver 226, and a synchronization detection unit 227. The MOST controller 3 has a PLL 31.

  A transmission digital data string TX is output from the MOST controller 3 to the transmission unit 22. Then, the transmission digital data sequence TX is input to the data mapping unit 222 via the selector 221. The selector 221 selects the transmission digital data string TX output from the MOST controller 3 when the synchronization detection unit 227 described later detects the synchronization of the PLL 31 included in the MOST controller 3 and inputs the synchronization detection signal CS. The data mapping unit 222 is input. On the other hand, when the selector 221 does not detect the synchronization of the PLL 31 included in the MOST controller 3 in the synchronization detector 227 (that is, does not input the synchronization detection signal CS), the selector 221 receives the bypass digital data string BX output from the receiver 21. The data is selected and input to the data mapping unit 222. Since the operation of the transmission unit 22 described later is the same for the transmission digital data sequence TX and the bypass digital data sequence BX, the operation for the transmission digital data sequence TX will be representatively described in the following description.

  The data mapping unit 222 collects the transmission digital data sequence TX for each predetermined bit to form a data symbol, performs mapping processing using a conversion table, and outputs the data symbol to the digital filter 223. Specifically, the data mapping unit 222 converts the serial transmission digital data string TX into parallel in order to perform multilevel transmission. When the communication protocol is MOST, 2-bit information with 1 symbol is output from the MOST controller 3 as a transmission digital data string TX. Therefore, the data mapping unit 222 converts the serially input data into 2-bit parallel data. Convert. Then, the data mapping unit 222 converts the parallel data for every 2 bits converted based on the reproduction clock CD reproduced and locked by the synchronization detection unit 216 of the reception unit 21 or the transmission clock output from the PLL 31 of the MOST controller 3. Is mapped to one of the eight-valued symbols. In this mapping, in order to perform clock recovery in another data transmission apparatus 1 arranged on the receiving side, parallel data for each 2 bits is alternately assigned to the upper 4 symbols and the lower 4 symbols among the 8-level symbols. . Further, in order to exclude the influence of fluctuations and differences in DC components between transmission and reception, mapping is performed based on the difference from the previous value.

  The digital filter 223 is, for example, a roll-off filter, performs a filtering process on the mapped data, and outputs the filtered data to the D / A converter 224. The digital filter 223 is a waveform shaping filter for suppressing the band limitation and the intersymbol interference of the electric signal to be transmitted. For example, an FIR filter having a roll-off rate of 100% is used.

  The D / A converter 224 converts the signal output from the digital filter 223 into an analog signal. For example, it is a 12-bit D / A converter operating at 100 MHz, and an analog signal so that a sine wave in which the transmission symbol value alternately has the maximum or minimum amplitude level can be output at the output terminal of the differential driver 226. Is output. The low pass filter 225 attenuates the high frequency from the analog signal output from the D / A converter 224 and inputs the attenuated frequency to the differential driver 226.

  The differential driver 226 amplifies the intensity of the analog signal output from the low-pass filter 225, converts it into a differential signal, and sends it to the transmission line 11. The differential driver 226 transmits an electrical signal to be sent to one side (plus side) conductor of the transmission line 11 with respect to a set of two conductors included in the transmission line 11, and a signal opposite to the electrical signal. Is transmitted to the other side (minus side) of the transmission line 11. As a result, since the electrical signals on the plus side and the minus side are transmitted as one pair to the transmission line 11, the mutual electrical signals cancel each other's changes in the electrical signals, and radiation noise from the transmission line 11 and Electric influence from the outside can be reduced. As described above, the transmission unit 22 performs mapping, filtering, and DA conversion processing, and thus the electrical signal having a waveform with a predetermined period in which the transmission digital data sequence TX is mapped to one of a plurality of signal levels. Is output.

  The synchronization detection unit 227 detects a data frame included in the transmission digital data sequence TX based on the transmission digital data sequence TX and the transmission clock output from the MOST controller 3, and periodically detects a frame header included in the data frame, for example. By detecting this, establishment of synchronization of the MOST controller 3 is detected. Then, when the synchronization detection unit 227 detects the synchronization establishment of the MOST controller 3, the synchronization detection unit 227 outputs a synchronization detection signal CS to the selector 221.

  On the other hand, the differential receiver 211 of the receiving unit 21 receives an electrical signal (differential signal) sent from the previous data transmission device 1 via the transmission path 11. The differential receiver 211 converts the differential signal into a voltage signal and outputs the voltage signal to the low-pass filter 212. As described above, the plus and minus electrical signals are transmitted as one pair with respect to a set of two conductors included in the transmission line 11, and the differential receiver 211 is connected to the plus and minus sides. Since the signal is judged from the difference between the two, it is effective against an external electrical influence.

  The low-pass filter 212 attenuates high-frequency noise mixed in the voltage signal output from the differential receiver 211 and inputs the attenuated noise to the A / D converter 213. The A / D converter 213 converts the voltage signal output from the low-pass filter 212 into a digital signal and outputs the digital signal to the digital filter 214.

  The digital filter 214 performs a filtering process on the digital signal output from the A / D converter 213, and includes, for example, a roll-off filter. The digital filter 214 is a waveform shaping FIR filter that removes noise from the digital signal output from the A / D converter 213. Combined with the above-described roll-off filter (digital filter 223) on the transmission side, a roll-off characteristic without intersymbol interference is realized.

  Also, the synchronization detection unit 216 regenerates the clock of the received data by regenerating the clock component of the signal received from the transmission path 11 output from the A / D converter 213, and the maximum or minimum of the transmission waveform described above. The data symbol timing that becomes the amplitude point is detected. The reproduction clock CD of the synchronization detection unit 216 is used as a clock for the determination processing unit 215 and the data mapping unit 222.

  The determination processing unit 215 performs inverse mapping processing on the digital signal output from the digital filter 214, decodes it into a data symbol, converts it into a received digital data string RX, and outputs it to the MOST controller 3. Specifically, the determination processing unit 215 calculates a difference value between the reception symbol value output from the digital filter 214 and the previous symbol value based on the data symbol timing detected by the synchronization detection unit 216. Thus, by determining the received symbol value based on the difference value with respect to the previous symbol value, it is possible to cancel the overall voltage change when transmitting from the transmission side to the data transmission device 1 on the reception side. Then, the determination processing unit 215 performs data determination for each difference value based on a determination level set in an initialization process described later, and performs a reverse mapping process on the determination value. That is, the inverse mapping process of the determination processing unit 215 decodes the data before mapping by the mapping process on the transmission side using the determination value based on the data symbol timing detected by the synchronization detection unit 216. By the reverse mapping process, the determination value is converted into parallel data. Then, the determination processing unit 215 converts the parallel data subjected to the reverse mapping process into a serial received digital data string RX and outputs the serial data to the MOST controller 3. The received digital data sequence RX is also output to the selector 221 as a bypass digital data sequence BX. Then, when the selector 221 selects the bypass digital data string BX, the selector 221 outputs the data to the data mapping unit 222 of the transmission unit 22.

  The CPU 4 controls the operation of the MOST controller 3 by transmitting and receiving a control signal CL to and from the MOST controller 3. Further, the CPU 4 outputs a reset signal RS to each of the MOST controller 3 and the transmission / reception unit 2, thereby initial standby state in which the MOST controller 3 and the transmission / reception unit 2 do not transmit / receive data (hereinafter, this state is reset). State)), or cancel that state. The CPU 4 is serially connected to the CPU 4 of another data transmission apparatus 1 via the transmission line 12. In the case of the master data transmission device 1a, the other CPU 4 is instructed to select the reset state or its release. Further, in the case of the slave data transmission devices 1b to 1n, the master CPU 4 is instructed to select its own reset state or its release.

  In the data transmission system configured as described above, initialization processing is performed on the MOST controllers 3a to 3n which are the link layers of the protocol and the transmission / reception units 2a to 2n which are the physical layers in order to define the mechanical connection. During the initialization operation, the clock synchronization of each of the data transmission apparatuses 1a to 1n is established and a determination level that is a reference for data determination is set. After the link layer and physical layer initialization processing is completed, all data transmission apparatuses 1 start data communication with each other using the physical layer and the link layer. Hereinafter, an operation mode in which the data transmission apparatus 1 performs data communication using the physical layer and the link layer is referred to as a “normal mode”. In addition, since the operation | movement from which all the data transmission apparatuses 1 transfer to a normal mode from the initialization process in the said data transmission system is the same as that of the conventional data transmission system demonstrated by background art, detailed description is demonstrated here. Omitted.

  In the data transmission system of the present invention, a part of the slave data transmission apparatus 1 can perform data transmission using only the physical layer (hereinafter, this data transmission is referred to as “bypass mode”). That is, the data transmission device 1 operating in the bypass mode sends the data received from the previous data transmission device 1 to the subsequent data transmission device 1 without going through the link layer (MOST controller 3). For example, the data transmission device 1a and the data transmission device 1 to which the connection device 10 composed of a monitoring camera, a security system, or the like is connected are operated in the normal mode, and the data transmission to which another connection device 10 is connected is performed. It is possible to operate the device 1 in the bypass mode. Hereinafter, an operation in which a part of the data transmission apparatus shifts from the normal mode to the bypass mode and then returns to the normal mode will be described with reference to FIGS. 3 and 4. 3 is a flowchart of the first half showing an operation in which some data transmission apparatuses 1 shift to the bypass mode in a data transmission system in which all the data transmission apparatuses 1 are operating in the normal mode. FIG. It is a flowchart of the latter half part which shows the operation | movement which returns to the normal mode from the said bypass mode in the transmission system.

  In FIG. 3, when all the data transmission apparatuses 1 are operating in the normal mode, the CPU 4a of the master data transmission apparatus 1a receives an instruction to shift a part of the data transmission apparatus 1 to the bypass mode (step S11). ). For example, the transfer instruction may be received by the CPU 4a in response to the operation of the user of the data transmission system by operating a predetermined SW, or the user may receive the key SW of the vehicle at the accessory position (that is, the engine stop). In this mode, the CPU 4a may receive it in response to the operation. As described above, when a CPU for controlling the bypass mode is separately provided in the data transmission system, the CPU receives the transition instruction. Hereinafter, in order to make the description more specific, the master CPU 4a is serially connected to the CPUs 4b to 4n of the other data transmission apparatuses 1b to 1n via the transmission line 12, and is in bypass mode with respect to the other CPUs 4b to 4n. A case where the selection process is instructed will be described.

  Next, the master CPU 4a starts a reset process for resetting the transmitting / receiving unit 2a and the MOST controller 3a of its own device (step S12), and connects the transmission line 12 to the other slave CPUs 4b to 4n. An instruction to perform a reset process is issued via Based on this instruction, the slave CPUs 4b to 4n also start reset processing for resetting the transmitting / receiving units 2b to 2n and the MOST controllers 3b to 3n of the own device (steps S41 and S71). The CPUs 4a to 4n send reset signals RS for resetting the transmitting / receiving units 2a to 2n and the MOST controllers 3a to 3n of the own device (steps S13, S42, and S72). The transmission / reception units 2a to 2n and the MOST controllers 3a to 3n enter the reset state by receiving the reset signal RS for setting the reset state (steps S14, S43, and S73). With these operations, all link layers and physical layers of the data transmission system are reset.

  Next, after elapse of a predetermined time from the reset process, the CPUs 4a to 4n output reset signals RS for canceling the reset state of the transmission / reception units 2a to 2n to the transmission / reception units 2a to 2n, respectively (steps S15, S44, and S74). . And the transmission / reception parts 2a-2n each start the physical layer initialization process by receiving the reset signal RS which cancels | releases a reset state (step S16, S45, and S75).

  Hereinafter, the physical layer initialization process will be described in detail. First, the master transmission / reception unit 2a transmits a lock signal to the transmission line 11 based on an output frequency using the resonator of the own device as a reference frequency. This lock signal is, for example, a sine wave signal based on the clock frequency of the master data transmission device 1a.

  On the other hand, the slave transmission / reception unit 2b receives the lock signal from the transmission line 11, performs clock recovery at the synchronization detection unit 216b, and sets a reception PLL. Then, the transmission / reception unit 2b transmits a lock signal to the transmission line 11 based on the reproduction clock of the reception PLL. Each of the other slave transmission / reception units 2c to 2n also receives the lock signal sent from the data transmission device 1 on the upstream side of its own device, regenerates the clock, sets the reception PLL, and then regenerates the reception PLL. Based on the clock, a lock signal is transmitted to the data transmission device 1 on the downstream side. Then, the master transmission / reception unit 2a receives the lock signal transmitted from the upstream transmission / reception unit 2n, performs clock recovery, and sets a reception PLL.

  Next, the master transmission / reception unit 2 a generates a training signal for setting a determination level as a data determination reference with the slave transmission / reception unit 2 b arranged downstream, and transmits the training signal to the transmission line 11. To do. The training signal includes, for example, a clock reproduction sine wave in which the maximum and minimum amplitude levels appear alternately, a training pattern header (for example, the maximum or minimum amplitude level continues for a predetermined period), and each data transmission apparatus 1. And a training pattern which is a known data pattern. As the training pattern, a PN pattern signal or the like in which all the data symbol values are included and various patterns appear is used.

  The slave transmitting / receiving unit 2 b receives the training signal from the transmission line 11, immediately generates a training signal with the downstream data transmission device 1 c, and transmits the training signal to the transmission line 11. Then, the transmitting / receiving unit 2b uses the received training signal in the receiving unit 21b of its own apparatus to set a determination level for determining a threshold value of the transmission level for each symbol value, Each judgment value with the judgment level as a boundary is set. The other slave transmission / reception units 2c to 2n also receive the training signal sent from the upstream data transmission device 1, and immediately transmit the training signal of the own device to the downstream data transmission device 1. Similarly, the transmission / reception units 2c to 2n of the other slaves also use the training signals received from the upstream data transmission device 1 in the reception units 21c to 21n, respectively, to determine the transmission level threshold value for each symbol value. Each determination level is set to set the determination level, and a determination value with the determination level as a boundary is set. The master transmission / reception unit 2a also uses the training signal received from the transmission / reception unit 2n to set a determination level for determining a transmission level threshold value for each symbol value. Set each judgment value with as the boundary.

  As a result, the physical layer initialization process of the data transmission system is completed, and the respective physical layers become ready for data communication with each other. Then, the transmission / reception units 2a to 2n output initialization process completion notifications indicating that the initialization process has been completed to the respective CPUs 4a to 4n. In addition, in order for all the transmission / reception units 2a to 2n to output the initialization processing completion notification in cooperation, the master transmission / reception unit 2a prompts the other transmission / reception units 2b to 2n to output the initialization processing completion notification. A signal may be output to the transmission line 11. In addition, each of the transmission / reception units 2a to 2n may output initialization process completion notifications to the CPUs 4a to 4n as a predetermined time elapses after the determination value setting process is executed. Then, the CPUs 4a to 4n determine whether or not the physical layer initialization process is completed by waiting for the initialization process completion notification output from the transmission / reception units 2a to 2n (steps S17, S46, and S76).

  Next, when the initialization process completion notification is notified from the transmission / reception unit 2a, the CPU 4a outputs a reset signal RS for canceling the reset state of the MOST controller 3a to the MOST controller 3a (step S18). Then, the CPU 4a sends an instruction to prohibit the reset release of the link layer to the CPUs 4b to 4n included in the data transmission apparatuses 1b to 1n operating in the bypass mode via the transmission line 12. The CPUs 4b to 4n from which the CPU 4a sends an instruction to prohibit the reset release are set in advance. For example, the data transmission device 1a and the data transmission device 1 to which the connection device 10 composed of a monitoring camera, a security system, or the like is connected are operated in the normal mode, and the data transmission to which another connection device 10 is connected is performed. When the device 1 is operated in the bypass mode, an instruction for prohibiting reset release is sent only to the CPU 4 of the data transmission device 1 operated in the bypass mode. The instruction for prohibiting the reset release may be sent during the reset process in steps S12, S41, and S71. The CPUs 4b to 4n included in the data transmission apparatuses 1b to 1n operating in the normal mode automatically cancel the link layer reset state as will be described later. However, the CPU 4a also cancels the link layers to the CPUs 4b to 4n. An instruction to release the reset state may be sent.

  On the other hand, among the CPUs 4b to 4n, those that have not received the instruction for prohibiting the reset release are automatically reset in the MOST controllers 3b to 3n when the initialization processing completion notification is notified from the transmission / reception units 2b to 4n. A reset signal RS for releasing the state is output to the MOST controllers 3b to 3n (step S47). Of the CPUs 4b to 4n, those that have received the instruction to prohibit the reset release continue the reset state of the MOST controllers 3b to 3n when the initialization processing completion notification is notified from the transmission / reception units 2b to 4n. (Step S77).

  Next, in steps S18 and S47, the MOST controller 3 to which the reset signal RS for releasing the reset state is input starts link layer initialization processing (steps S19 and S48).

  Hereinafter, the link layer initialization process when a part of the data transmission apparatus 1 operates in the bypass mode will be described in detail. The master MOST controller 3a cancels its reset state by receiving the reset signal RS, and performs its initial setting by receiving the control signal CL. The PLL 31a included in the MOST controller 3a operates using the frequency output from the oscillator included in the transmission / reception unit 2a as a reference frequency. Then, the MOST controller 3a outputs initialization data for performing initialization processing such as frame synchronization with other MOST controllers 3 to the transmission unit 22a as a transmission digital data string TX.

  The synchronization detection unit 227a of the transmission unit 22a detects a data frame included in the initialization data from the initialization data output from the MOST controller 3a and its transmission clock, and periodically detects a frame header included in the data frame. Thus, the establishment of synchronization of the MOST controller 3a is detected. Then, when detecting the synchronization establishment of the MOST controller 3a, the synchronization detection unit 227a outputs a synchronization detection signal CS to the selector 221a. When the synchronization detection signal CS is input, the selector 221a causes the data mapping unit 222a to input initialization data output from the MOST controller 3a. The initialization data is subjected to the mapping process and filtering process described above by the transmission unit 22a, converted into an analog signal, and transmitted to the transmission line 11.

  The receiving unit 21b included in the slave data transmission device 1b receives the initialization data from the transmission line 11, converts the initialization data into a digital signal as described above, and performs filtering processing and inverse mapping processing. When the link layer reset state is released by the operation of step S47 in the slave data transmission apparatus 1b, the initialization data is output from the determination processing unit 215b to the MOST controller 3b as the received digital data string RX. Then, the MOST controller 3b establishes frame synchronization with the master MOST controller 3a using the input initialization data, locks the PLL 31b, and then outputs the initialization data to the transmitter 22b. The synchronization detection unit 227b of the transmission unit 22b detects a data frame included in the initialization data from the initialization data output from the MOST controller 3b and its transmission clock, and periodically detects a frame header included in the data frame. By doing so, the synchronization establishment of the MOST controller 3b is detected. Then, when detecting the synchronization establishment of the MOST controller 3b, the synchronization detection unit 227b outputs a synchronization detection signal CS to the selector 221b. When the synchronization detection signal CS is input, the selector 221b causes the data mapping unit 222b to input initialization data output from the MOST controller 3b. Then, the initialization data is subjected to the mapping process and filtering process described above by the transmission unit 22b, converted into an analog signal, and sent to the transmission line 11. Until the synchronization detection unit 227b outputs the synchronization detection signal CS to the selector 221b, the selector 221b causes the data mapping unit 222b to input the initialization data output from the determination processing unit 215b as the bypass digital data string BX. Then, the bypass digital data string BX (that is, initialization data bypassing the MOST controller 3b) is converted into an analog signal after being subjected to the mapping process and the filtering process described above by the transmission unit 22b, and sent to the transmission line 11.

  On the other hand, when the link layer reset state is continued in the operation of step S77 in the slave data transmission device 1b (that is, release of the reset state is prohibited), the synchronization detection unit 227b includes the MOST controller 3b. Synchronization establishment cannot be detected. Therefore, since the synchronization detection signal CS is not output to the selector 221b, the selector 221b always causes the initialization data output from the determination processing unit 215b to be input to the data mapping unit 222b as the bypass digital data string BX. Then, the bypass digital data string BX (that is, initialization data bypassing the MOST controller 3b) is converted into an analog signal after being subjected to the mapping process and the filtering process described above by the transmission unit 22b, and sent to the transmission line 11. That is, the data transmission device 1 in which the link layer reset state continues continues to send initialization data received from the upper data transmission device 1 to the lower data transmission device 1 via only the physical layer of the data transmission device 1 itself. .

  The other slave MOST controllers 3c to 3n perform the same operation as the above-described slave MOST controller 3b. That is, the MOST controller 3 whose link layer reset state has been released by the operation of step S47 establishes frame synchronization with the master MOST controller 3a using the input initialization data, and the initialization data Are output to the transmitter 22. On the other hand, the MOST controller 3 in which the link layer reset state is continued in the operation of the above step S77 transmits the initialization data received from the upper data transmission device 1 to the lower data transmission only through the physical layer of the own device. Send to device 1.

  Then, the master MOST controller 3a determines the establishment of the network of the entire data transmission system in the link layer initialization process started in step S19. For example, the MOST controller 3a sends a network establishment confirmation signal via the transmitter 22a, and the MOST controller 3a receives the signal a predetermined number of times via the other data transmission devices 1b to 1n and the receiver 21a. Determine that the network has been established. Then, the MOST controller 3a gives an identifier indicating network establishment to a predetermined data frame, and transmits the data frame to all the other slave data transmission apparatuses 1b to 1n. Further, after the network is established, the MOST controller 3a ends the link layer initialization process, and outputs a control signal CL indicating the end to the CPU 4a. The CPU 4a waits for the link layer initialization process of the MOST controller 3a to end, receives the control signal CL indicating the end, and determines the end of the initialization process (step S20). Then, the CPU 4a outputs a control signal CL for instructing the MOST controller 3a to start data communication, and the MOST controller 3a receives the control signal CL for instructing start of data communication. Data communication is started (step S21).

  On the other hand, the slave MOST controller 3 whose link layer reset state is released by the operation of step S47 receives the data frame to which the identifier indicating the network establishment output from the master data transmission device 1a is attached. Thus, the establishment of the network is determined. Then, after the network is established, the MOST controller 3 ends the link layer initialization process, and outputs a control signal CL indicating the end to the CPU 4. The CPU 4 waits for the link layer initialization process of the MOST controller 3 to end, receives the control signal CL indicating the end, and determines the end of the initialization process (step S49). Then, the CPU 4 outputs a control signal CL for instructing the MOST controller 3 to start data communication, and the MOST controller 3 receives the control signal CL for instructing start of data communication. Data communication is started (step S50).

  Also, the MOST controller 3 in which the link layer reset state is continued in the operation of step S77 also performs the physical frame of its own device with respect to the data frame to which the identifier indicating the network establishment received from the upper data transmission device 1 is assigned. The data is sent to the lower data transmission apparatus 1 only through the layer. Then, the data transmission device 1 in which the link layer reset state is continued, even if another data transmission device 1 starts data communication (steps S21 and S50), the data transmission device 1 from the upper data transmission device 1 through the data communication. It operates in a bypass mode in which transmitted data is sent to the lower data transmission apparatus 1 only through the physical layer of the own apparatus (step S78).

  In the data transmission device 1 that operates in the bypass mode, an electrical signal sent from the previous data transmission device 1 via the transmission path 11 is input to the differential receiver 211 of the reception unit 21. The input electrical signal is filtered and converted into digital data by the low-pass filter 212, the A / D converter 213, and the digital filter 214. Then, the digital data is decoded into a data symbol by the determination processing unit 215 and output to the transmission unit 22 as a bypass digital data string BX. The transmission unit 22 handles the bypass digital data sequence BX in the same manner as the transmission digital data sequence TX. That is, the bypass digital data string BX is subjected to mapping processing and filtering processing by the transmission unit 22 and converted into an analog signal, and then transmitted as an electric signal to the subsequent data transmission apparatus 1 via the transmission path 11. Therefore, in the physical layer of the data transmission apparatus 1 that operates in the bypass mode, the filtering process, the A / D conversion process, and the data determination process are performed on the received electrical signal, and then the mapping process, the filtering process, and the D Since the A / A conversion process is performed and the electrical signal is transmitted to the subsequent stage, data transmission can be performed with reduced deterioration of data indicated by the transmitted / received electrical signal. Further, in the data transmission device 1 operating in the bypass mode, the MOST controller 3 continues to be in the reset state, and therefore the MOST controller 3 does not perform data transmission / reception processing. That is, the power consumption of the MOST controller 3 can be reduced. Furthermore, generally, since the power supply to the connection device 10 (see FIG. 1) connected to the reset MOST controller 3 is also stopped, the connection device 10 connected to the data transmission apparatus 1 operating in the bypass mode is stopped. Power consumption can be greatly reduced.

  Next, with reference to FIG. 5, the state of each data transmission apparatus 1 will be described in time series in the above-described bypass mode transition processing of the data transmission system. FIG. 5 is a sequence diagram showing, in time series, the state in which each data transmission device 1 operates in the above-described link layer and physical layer transition processing of the data transmission system.

  In FIG. 5, the link layer (MOST controller 3) and the physical layer (transmission / reception unit 2) of each data transmission apparatus 1 are all reset by the reset process of the CPU 4. Then, the physical layer of each data transmission apparatus 1 performs a physical layer initialization process by a reset release process of the CPU 4. Next, the link layer of the data transmission device 1 operating in the master mode and the normal mode performs the link layer initialization process by the reset release process of the CPU 4 after the physical layer initialization process ends. After the link layer initialization process is completed, the data transmission device 1 operating in the master and normal mode starts data communication using the physical layer and link layer of the device itself. On the other hand, as can be seen from comparison with FIG. 7, the link layer of the data transmission device 1 operating in the bypass mode is not subjected to the reset release processing by the CPU 4 even when the physical layer initialization processing of the own device is completed. Therefore, the reset state continues. Therefore, after the link layer initialization process of the other data transmission apparatus 1 is completed, the data transmission apparatus 1 operating in the bypass mode performs data transmission using only the physical layer by bypassing the link layer of the own apparatus.

  Next, with reference to FIG. 4, the operation of returning from the bypass mode to the normal mode in the data transmission system will be described. In FIG. 4, when some data transmission apparatuses 1 are operating in the bypass mode, the CPU 4a of the master data transmission apparatus 1a waits for an instruction to cancel the bypass mode (step S22). For example, the release instruction may be received by the CPU 4a in response to the operation of the user of the data transmission system by operating a predetermined SW, or the user operates the key SW of the vehicle to the engine start position. Thus, the CPU 4a may receive it in response to the operation. As described above, when a CPU for controlling the bypass mode is separately provided in the data transmission system, the CPU receives the release instruction. Hereinafter, in order to make the description more specific, the master CPU 4a is serially connected to the CPUs 4b to 4n of the other data transmission apparatuses 1b to 1n via the transmission line 12, and is in bypass mode with respect to the other CPUs 4b to 4n. A case where the cancellation process is instructed will be described.

  When the master CPU 4a receives the bypass mode release instruction in step S22, the master CPU 4a starts reset processing for resetting the transmitting / receiving unit 2a and the MOST controller 3a of the own device (step S23), and the CPU 4b of the other slaves. Instructions for reset processing are also sent to .about.4n via the transmission line 12. Based on this instruction, the slave CPUs 4b to 4n also start reset processing for resetting the transmitting / receiving units 2b to 2n and the MOST controllers 3b to 3n of the own device (steps S51 and S79). The CPUs 4a to 4n send reset signals RS for resetting the transmitting / receiving units 2a to 2n and the MOST controllers 3a to 3n of the own device (steps S24, S52, and S80). Then, the transmission / reception units 2a to 2n and the MOST controllers 3a to 3n enter the reset state by receiving the reset signal RS for setting the reset state (steps S25, S53, and S81). With these operations, all link layers and physical layers of the data transmission system are reset.

  Next, after a predetermined time has elapsed from the reset process, the CPUs 4a to 4n output reset signals RS for canceling the reset states of the transmission / reception units 2a to 2n to the transmission / reception units 2a to 2n, respectively (steps S26, S55, and S82). . And the transmission / reception parts 2a-2n each start the physical layer initialization process by receiving the reset signal RS which cancels | releases a reset state (step S27, S55, and S83). Since these physical layer initialization processes are the same as steps S16, S17, S45, S46, S75, and S76 described above, detailed description thereof is omitted.

  Next, when the initialization process completion notification is notified from the transmission / reception unit 2a, the CPU 4a outputs a reset signal RS for canceling the reset state of the MOST controller 3a to the MOST controller 3a (step S29). However, when the bypass mode is released, the CPU 4a does not send the instruction to prohibit the reset release of the link layer described above via the transmission line 12. The CPUs 4b to 4n included in the data transmission apparatuses 1b to 1n operating in the normal mode automatically cancel the reset state of the link layer when the reset release is not prohibited. However, the CPU 4a has all the CPUs 4b to 4n. An instruction to release the reset state of the link layer may be sent to.

  On the other hand, when the initialization processing completion notification is notified from the transmission / reception units 2b to 4n, the CPUs 4b to 4n automatically output a reset signal RS for releasing the reset state of the MOST controllers 3b to 3n to the MOST controllers 3b to 3n. (Steps S57 and S85).

  Next, in steps S29, S57, and S85, the MOST controller 3 to which the reset signal RS for releasing the reset state is input starts link layer initialization processing (steps S30, S58, and S86). Since these link layer initialization processes are the same as steps S19, S20, S48, and S49 described above, detailed description thereof will be omitted.

  Next, the CPU 4a outputs a control signal CL instructing the MOST controller 3a to start data communication, and the MOST controller 3a receives the control signal CL instructing start of data communication. Data communication is started (step S32). On the other hand, the slave CPUs 4b to 4n output control signals CL for instructing the start of data communication to the respective MOST controllers 3b to 3n, and the MOST controllers 3b to 3n receive the control signal CL for instructing the start of data communication. Then, data communication with the other data transmission apparatus 1 is started (steps S60 and S88). Therefore, when a transition is made from a state in which some data transmission apparatuses 1 operate in the bypass mode to a state in which all data transmission apparatuses 1 operate in the normal mode, initialization is performed for all physical layers and link layers. Processing is performed and data communication is started.

  In the data transmission system operating in the bypass mode in the data transmission system of the present embodiment, the MOST controller of the own apparatus is in a reset state, and the MOST controller does not perform data transmission / reception processing, so that the power consumption of the MOST controller is reduced. Can do. In general, since power supply to the connected device connected to the reset MOST controller is also stopped, the power consumption of the connected device connected to the data transmission device operating in the bypass mode can be greatly reduced. it can. Therefore, when operating only some of the connected devices connected to the data transmission system, the power consumption of the entire system is greatly reduced by operating the data transmission device connected to the connected devices that are not operated in the bypass mode. can do. Further, in the physical layer of the data transmission device operating in the bypass mode, the filtering process, the A / D conversion process, and the data determination process are performed on the received electrical signal, and then the mapping process, the filtering process, and the D / D Since the A conversion process is performed and the electric signal is transmitted to the subsequent stage, data transmission can be performed with reduced deterioration of data indicated by the electric signal to be transmitted and received.

  In the description of this embodiment, the selector of the transmission unit is switched based on the synchronization establishment of the MOST controller. However, the selector switching method is not limited to this. For example, the selector may perform switching according to the presence / absence of a transmission digital data string output from the MOST controller, or may be directly controlled by the CPU of the own device. That is, the selector may be switched by control from the outside of the transmission unit.

  In the description of the present embodiment, the protocol defined by MOST is used as the link layer of the data transmission system, but the present invention is not limited to the protocol defined by MOST. For example, it goes without saying that the present invention can be similarly applied to a custom link layer other than the link layer defined by MOST.

  A data transmission method, a data transmission system, and a data transmission device according to the present invention are a data transmission between data transmission devices connected by a transmission line in a ring type or the like that needs to reduce power consumption of the entire system. It is useful as a method, a data transmission system, and a data transmission apparatus.

The block diagram which shows the structure of the data transmission system which concerns on one Embodiment of this invention. The block diagram which shows the structure of the data transmission apparatus 1 of FIG. FIG. 1 is a first half flowchart illustrating an operation in which some data transmission apparatuses 1 shift to a bypass mode in a data transmission system in which all the data transmission apparatuses 1 in FIG. 1 operate in the normal mode. Flowchart in the second half showing the operation of returning from the bypass mode to the normal mode in the data transmission system of FIG. FIG. 3 is a sequence diagram showing, in time series, the state in which each data transmission device 1 operates in the link layer and physical layer migration processing of the data transmission system of FIG. Block diagram showing the configuration of a conventional data transmission system using telecommunications FIG. 6 is a sequence diagram showing initialization processing in the data transmission system of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Data transmission apparatus 2 ... Transmission / reception part 21 ... Reception part 211 ... Differential receiver 212, 225 ... Low pass filter 213 ... A / D converter 214, 223 ... Digital filter 215 ... Determination processing part 216, 227 ... Synchronization detection part 22 ... Transmission unit 221, selector 222, data mapping unit 224, D / A converter 226, differential driver 3, MOST controller 31, PLL
4 ... CPU
DESCRIPTION OF SYMBOLS 10 ... Connection apparatus 11 ... Transmission path 12 ... Transmission line

Claims (10)

A data transmission system including a plurality of data transmission devices connected in a ring shape via a transmission line, each data transmission device transmitting and receiving transmission signals to and from each other,
The data transmission devices are respectively
A processing unit for processing transmission / reception data based on a predetermined communication protocol;
A transmission signal is generated based on the transmission data processed by the processing unit and output to a subsequent data transmission device, and reception data is generated based on the transmission signal output from the previous data transmission device, and the processing is performed. A transmission / reception unit that outputs to the unit ;
A control unit that controls operations of the processing unit and the transmission / reception unit,
The control units are connected to be able to communicate with each other via a transmission line,
The first data transmission device, which is at least one of the plurality of data transmission devices, generates reception data according to the transmission signal output from the previous data transmission device in the transmission / reception unit, and then receives the reception data. In response to the transmission signal and output it to the subsequent data transmission device.
Of the plurality of data transmission devices, a second data transmission device different from the first data transmission device,
In the transmission / reception unit, the reception data generated according to the transmission signal output from the preceding data transmission device is processed in the processing unit based on the communication protocol,
In accordance with the transmission data processed based on the communication protocol in the processing unit, a transmission signal is generated in the transmission / reception unit and output to the data transmission device in the subsequent stage ,
The control unit included in the first data transmission device performs control to maintain a reset state in which the data processing operation of the processing unit of the own device is stopped based on an instruction input via the transmission line. A data transmission system. Each of the transmitting and receiving units is
A bypass path for bypassing the processing unit of the own device and outputting the received data;
A selector that selects one of the transmission data output from the processing unit and the reception data output from the bypass path according to an operation state of the processing unit and outputs the selected data to the transmission side of the transmission / reception unit. ,
Said selector, wherein the first data transmission device has, in response to an instruction from the outside of the transceiver unit of the own device, and selects the reception data output from the bypass path, according to claim 1 The data transmission system described in 1. Each of the transmitting and receiving units is
A bypass path for bypassing the processing unit of the own device and outputting the received data;
A selector that selects one of the transmission data output from the processing unit and the reception data output from the bypass path according to an operation state of the processing unit and outputs the selected data to the transmission side of the transmission / reception unit. ,
The selector included in the first data transmission device selects the reception data output from the bypass path when the processing unit of the own device is in a reset state in which the data processing operation is stopped. The data transmission system according to claim 1 . Each of the transmitting and receiving units is
A data mapping unit that maps each symbol of the transmission data to one of a plurality of signal levels to generate the transmission signal;
The data transmission system according to claim 1 , further comprising: a determination processing unit that generates the reception data based on a determination level for distinguishing and determining a plurality of signal levels of the transmission signal. The communication protocol used by the processing unit is MOST (Media Oriented).
The data transmission system according to claim 1 , wherein the data transmission system is defined by Systems Transport). A data transmission device that is connected to another device via a transmission line in a ring shape, and that transmits and receives transmission signals to and from other devices,
A processing unit for processing transmission / reception data based on a predetermined communication protocol;
A transmission signal is generated based on the transmission data processed by the processing unit and output to another device, and reception data is generated based on the transmission signal output from the other device and output to the processing unit. A transceiver unit ;
A control unit that controls operations of the processing unit and the transmission / reception unit,
The control unit is communicably connected to the control unit of another device via a transmission line,
In the first mode, the transmission / reception unit generates reception data according to a transmission signal output from another device, then generates a transmission signal according to the reception data and outputs the transmission signal to the other device,
In a second mode different from the first mode,
The transmission / reception unit outputs reception data generated according to a transmission signal output from another device to the processing unit,
The processing unit processes reception data output by the transmission / reception unit based on the communication protocol, and outputs transmission data processed based on the communication protocol to the transmission / reception unit,
The transmission / reception unit generates a transmission signal based on transmission data output from the processing unit and outputs the transmission signal to another device ,
The control unit performs control to maintain a reset state in which the data processing operation of the processing unit of the own apparatus is stopped based on an instruction indicating the first mode input via the transmission line. , Data transmission equipment. The transceiver unit is
A bypass path for bypassing the processing unit and outputting the received data;
A selector that selects one of the transmission data output from the processing unit and the reception data output from the bypass path according to an operation state of the processing unit and outputs the selected data to the transmission side of the transmission / reception unit. ,
The data transmission according to claim 6 , wherein the selector selects the reception data output from the bypass path in response to an instruction from the outside of the transmission / reception unit indicating the first mode. apparatus. The transceiver unit is
A bypass path for bypassing the processing unit and outputting the received data;
A selector that selects one of the transmission data output from the processing unit and the reception data output from the bypass path according to an operation state of the processing unit and outputs the selected data to the transmission side of the transmission / reception unit. ,
7. The selector according to claim 6 , wherein the selector selects the received data output from the bypass path when the processing unit is in a reset state in which data processing operation is stopped in the first mode. Data transmission equipment. The transceiver unit is
A data mapping unit that maps each symbol of the transmission data to one of a plurality of signal levels to generate the transmission signal;
The data transmission apparatus according to claim 6 , further comprising: a determination processing unit that generates the reception data based on a determination level for distinguishing and determining a plurality of signal levels of the transmission signal. The data transmission apparatus according to claim 6 , wherein the communication protocol used by the processing unit is defined by a Media Oriented Systems Transport (MOST).

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