JP2005252629A - Communication device and network system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication device with which transmission/reception performance can be improved even if a general-purpose electric wire is used for a transmission medium. <P>SOLUTION: Nodes where transceivers 16 and 26 and pulse transformers 17 and 27 are used for physical layer circuits 14 and 24 are connected through a channel 30. Middle points M are arranged in wire winding of a transceiver-side of the pulse transformers, and the middle points are connected to power source ground. When the number of turns on a primary side and that of a secondary side in the pulse transformers are set to be N01 and N02, a transformation ratio on appearance at the time of transmission becomes N02/(N01/2), and output voltage V00 can be enlarged. Even if the transformation ratio is adjusted to adopt impedance matching, V00 becomes not less than a prescribed value, and a transmission distance becomes long. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a communication device and a network system.

  PLC (programmable controller) used in FA (factory automation) inputs ON / OFF information of input devices such as switches and sensors, and performs logical operations according to a sequence program (user program) written in a ladder language. Execute. The PLC controls an object to be controlled by outputting a signal of ON / OFF information to an output device such as a relay, a valve, or an actuator according to the obtained calculation result. The above input device and output device may be directly connected to an input / output unit or the like constituting the PLC, or may be indirectly connected through various networks.

  Devices and equipment for sending and receiving data to and from the PLC exist at various production sites where the PLC is installed. Accordingly, devices / equipment installed near the PLC are connected to an input / output unit or the like to configure the PLC, and devices / equipment installed at a location away from the PLC are connected to the PLC via the network. . Communication via this network can be performed by, for example, master-slave communication. In this case, a slave is connected to the master unit constituting the PLC via a network cable (communication path), and the above-described devices and devices are connected to the slave.

  By the way, the above-mentioned master unit or slave needs to insulate the internal circuit and the communication path in a DC (direct current) manner in order to prevent destruction due to a loop current due to a ground potential difference or a surge voltage on the line. Therefore, a DC insulating member is usually interposed between the transceiver provided in the physical layer circuit directly connected to the communication path in the internal circuit and the connection port of the communication path. As such an insulating member, for example, a photocoupler, an insulation type DC-DC converter (or a dedicated power source for communication), a pulse transformer disclosed in Patent Document 1, and the like are used.

  FIG. 1 shows a physical layer circuit portion in a network using a conventional pulse transformer. As shown in FIG. 1, the primary side of the pulse transformer 1 is connected to the transceiver 2, and the secondary side of the pulse transformer 1 is connected to the communication path 3. When node # 00 is the transmitting station and node # 01 is the receiving station, the encoded data generated and output by the internal circuit (not shown) of the transmitting station is transmitted to the primary of the pulse transformer 1 via the transceiver 2. Given to the side. Then, since the secondary side of the pulse transformer 1 outputs encoded data having the same contents as the encoded data given to the primary side, the encoded data output to the secondary side passes through the communication path 3. To the node # 001.

  On the node # 01 side, the encoded data sent via the communication path 3 is given to the secondary side of the pulse transformer 1. Encoded data having the same content as the received code or data is output to the primary side of the pulse transformer and received by the transceiver 2. Therefore, the communication path 3 and the internal circuit (transceiver 2 and the like) are insulated from each other by the pulse transformer 1 so that data can be transmitted.

  The peak value (voltage) of the encoded data generated on the primary / secondary side of the pulse transformer 1 increases or decreases depending on the turn ratio (transformation ratio) between the primary winding and the secondary winding, but is the same for each node. When the physical layer circuit is applied, the output voltage output from the transceiver 2 on the transmission side is equal to the reception voltage when finally input to the transceiver 2 on the other side.

  That is, node # 00 is a transmitting station, node # 01 is a receiving station, V1 is a voltage appearing between ports AB of node # 00, V3 is a voltage appearing between ports AB of node # 01, and V0 is a communication path The voltage N1 / N2 appearing on 3 is defined as the turn ratio of the pulse transformer 1.

Then, the voltage V0 appearing on the communication path 3 when the node # 00 is transmitted is
V0 = (N2 / N1) × V1
It becomes.
The reception voltage V3 of the receiver at the time of reception of the node # 01 is
V3 = (N1 / N2) × V0
= (N1 / N2) × {(N2 / N1) × V1}
= V1
It becomes. Therefore, regardless of the transformation ratio of the pulse transformer 1, the output voltage on the transmission side appears as a reception voltage on the reception side.
JP 2001-156862 A

  However, the communication system using the conventional pulse transformer described above has the following problems. That is, the highest transmission performance and communication distance can be obtained when a dedicated transmission medium (cable) suitable for the transceiver is used. However, in the case of such a dedicated transmission medium, there is a problem that it is difficult to obtain and expensive as compared with a general-purpose electric wire such as a power supply line.

  On the other hand, in order to increase the types of inventory, there is a demand for the development of communication equipment that can be used as a transmission medium with a cable that is easily available as a general-purpose cable and that is inexpensive but originally in stock. However, when a general-purpose transmission medium such as a power supply line is simply used for a conventional communication path, impedance mismatch with the communication path occurs, and transmission quality may be deteriorated due to reflected waves.

In addition, since the transformation ratio of the pulse transformer 1 is considered to be unrelated to the peak value of transmission / reception, changing the transformation ratio matches the characteristic impedance of the communication path with the apparent impedance of the physical layer circuit being transmitted, It is possible to prevent deterioration in transmission quality due to double reflection of the reflected wave from the side and superimposition on the traveling wave. That is, impedance matching can be achieved by satisfying the following equation.
Z1 / Z0 = (N1 / N2) 2
Therefore, when N1 = 1, impedance matching can be achieved by setting N2 = (Z0 / Z1) 1/2.

  However, for example, if the setting for impedance matching is N2 <N1, the output voltage V0 of the pulse transformer becomes less than the input voltage V1, and the voltage of the signal transmitted through the communication path 3 becomes small. Therefore, there is a high possibility that the transmission distance will be shortened, or the signal will be distorted and garbled due to noise or the like, resulting in a decrease in communication performance.

  Furthermore, there is a demand for realizing a larger size and system with a single communication path, and in order to achieve such a demand, higher performance and communication distance than before are required. However, in the system using the conventional dedicated line, the transmission distance is limited, and in the system using the general-purpose line adopting impedance matching, the transmission / reception performance is higher than that when the transmission medium suitable for the transceiver is used. It cannot be improved.

  An object of this invention is to provide the communication apparatus and network system which can improve transmission / reception performance even if a general purpose electric wire is used for a transmission medium.

  A communication device according to the present invention is a serial communication device that performs data communication with another serial communication device via a communication path, and uses a transceiver and a pulse transformer in a physical layer circuit connected to the communication path. And connecting the winding on the communication path side of the pulse transformer to the communication path, connecting the winding on the transceiver side to the transceiver, and DC disconnecting between the communication path side and the transceiver side, A mid-point was provided in the winding on the transceiver side, and the mid-point was connected to the power supply ground.

  It is preferable to provide a current suppression resistor in series with a line connecting the transceiver and the pulse transformer and a line connecting the midpoint and the power supply ground. Of course, the installation of such a current suppression resistor is not essential.

  Furthermore, although there are various application locations of the communication device, for example, it can be either a master unit constituting a programmable controller or a slave or repeater connected to the master unit via a network. Further, the transformation ratio of the pulse transformer may be set so that impedance matching is established with the connected communication path.

  Furthermore, each communication device (transmission side) described above is configured such that one port A of the transceiver is a high output and the other port B is a low output, and the transmission voltage appearing between the ports A and B is V01, When the voltage appearing on the communication path to which the secondary side of the pulse transformer is connected is V00, and the number of turns on the primary and secondary sides of the pulse transformer is N01 and N02, the transceiver outputs a high output when the high output is made. The generated current reaches the primary winding of the pulse transformer and flows through the path from the midpoint of the primary winding to the power supply ground. A voltage of 2 × (N02 / N01) × V01 is generated between both terminals of the secondary winding, and the voltage may be set to a voltage V00 that appears on the communication path.

In addition, as a communication device that receives a signal output from the communication device, the reception voltage applied between one port A and the other port B of the transceiver is V03, and the secondary side of the pulse transformer is connected. The voltage V00 (= 2 × (N02 / N01) × V01) of the communication path is the pulse when the voltage appearing on the communication path is V00 and the turns of the primary and secondary sides of the pulse transformer are N01 and N02. When a current flows through the secondary winding as a result of being applied to the secondary side of the transformer, a voltage V03 generated between both terminals of the primary winding of the pulse transformer is a received voltage between the AB ports of the transceiver. The received voltage V03 of the transceiver is
V03 = (N01 / N02) × V00
= (N01 / N02) × {2 · (N02 · N01) × V01}
= 2 ・ V01
It is good to set so that.

  This is preferable because the reception voltage is twice the transmission voltage. The above-described equations and generated voltages are set in an ideal state where there is no loss in each device or communication path, and of course, as an actual device, it may decrease due to loss or the like. .

  In the network system according to the present invention, in a network system including a plurality of nodes connected via a communication path, the nodes are mounted with communication devices having the above-described configurations.

  According to the present invention, by connecting the midpoint provided in the pulse transformer to the power supply ground, the current path at the time of transmission and reception is changed, and the apparent transformation ratio can be changed, so that the transmission capability is increased. be able to. In other words, by connecting the midpoint provided in the pulse transformer to the power supply ground, the transformer transformation ratio at the time of transmission can be changed, the voltage of the signal output from the pulse transformer and sent to the communication path can be increased, and the communication distance Can be lengthened.

  Also, by appropriately setting the transformation ratio of the pulse transformer, matching the impedance of the physical layer with the line (communication path) at the time of transmission prevents the transmission quality from deteriorating due to the reflected wave being superimposed on the transmission wave. be able to. As a result, even if a transmission medium in which impedance mismatch occurs at the time of transmission (a cheap and easily available cable such as a general-purpose power supply line VCTF) is used, the transmission quality is not significantly reduced. Of course, even when the present invention is used, it is not hindered to use a dedicated line for the communication path as in the prior art.

  In the present invention, since the midpoint is provided in the winding on the transceiver side of the pulse transformer and it is connected to the power supply ground, the substantial transformation ratio at the time of transmission can be changed and output to the winding on the output side. The voltage can be increased, and transmission / reception performance can be improved even if a general-purpose electric wire is used as the transmission medium.

  FIG. 2 shows an example of a network system in the FA system. FIG. 2 shows a state where the master 10 and the slave 20 are connected via a communication path. That is, the main communication path 30 is connected to the master 10, and the slave 20 is directly connected to the main communication path 30. Further, the slave 20 may be connected to the sub communication path 32 branched from the main communication path 30 via the T branching device 31. Further, a terminating resistor 33 is connected to a location where the end of the communication path 30 is open.

  The master 10 is one unit constituting the PLC and is also referred to as a master unit. FIG. 3 shows an example of the internal structure of the master 10. The master 10 includes a CPU unit and a PLC bus interface unit 11 for transferring data, a MPU unit 12 for data processing / arithmetic processing, an operation / display unit 13 and a main part of the present invention. And a physical layer circuit 14 connected to the communication path 30.

  The PLC bus interface unit 11 includes an inter-unit connector 11a, a bus driver 11b, a three-terminal regulator 11c, and a level shifter 11d. The inter-unit connector 11a has a function of electrically and mechanically connecting to other adjacent units, and is connected to the power supply line and the PLC bus. The power supply voltage supplied by the power supply line between units is 5V.

  The bus driver 11b is an ASIC that exchanges data with the CPU unit via the PLC bus, and transmits and receives data via the internal shared memory. The access right to the shared memory is controlled by an internal register flag. The bus driver 11b has an interrupt generation function, and can interrupt the CPU unit to the main unit (master 10) and can interrupt the main unit (master 10) to the CPU unit.

  The three-terminal regulator 11c steps down 5V supplied from the PLC bus to 3.3V that is an operation power supply of the MPU unit 12, and supplies the 3.3V power supply to the MPU unit 12 as a power supply voltage. Since the operating voltage (5V) of the bus driver 11b and the operating voltage (3.3V) of the MPU unit 12 are different from each other, the level shifter 11d adjusts the voltage when transferring data between them (voltage conversion of signals). Is to do.

  The MPU unit 12 includes an MPU 12a, a volatile memory 12b composed of SRAM (static RAM), and a nonvolatile memory 12c composed of EEPROM. The nonvolatile memory 12c stores, for example, an abnormality history and a unit profile. The volatile memory 12b is used as a work memory. Then, the MPU 12a stores, for example, data from the CPU unit acquired via the bus driver 11b in the volatile memory 12b or reads data stored in the volatile memory 12b and adds information such as a transmission destination. Or create a message for a predetermined slave, send it to the physical layer circuit 14, acquire data from the slave received by the physical layer circuit 14, temporarily store it in the volatile memory 12 b, and bus at a predetermined timing Processing related to data transmission / reception such as passing to the driver 11b is performed.

  The operation / display unit 13 includes a number setting switch 13a for setting the unit number of the unit (master 10), an LED 13b as a display means, a mode setting switch 13c for setting various modes, and a connection node number setting / transmission speed. It has a dip switch 13d for performing various settings such as switching setting / communication mode setting. The number setting switch 13a and the mode setting switch 13c can be constituted by a rotary switch or the like. The LED 13b includes a single color indicator lamp, a 7 segment LED, and the like.

  The physical layer circuit 14 includes a communication ASIC 15, a transceiver 16, a pulse transformer 17, and a connector 18. The communication ASIC 15 encodes the data for transmission sent from the MPU 12a to create encoded data and passes it to the transceiver 16, or the received data sent from the slave 20 (transferred from the transceiver 16). The unnecessary signal is removed, and other necessary processes are performed to generate original signal data, and a function of performing a process of passing to the MPU 12a. The communication ASIC 15 may belong to the MPU unit 12 side.

  The transceiver 16 is disposed between the communication ASIC 15 and the primary side of the pulse transformer 17 and outputs transmission data received from the communication ASIC 15 at a predetermined timing. That is, ON / OFF of energization is controlled for the primary side of the pulse transformer 17 in accordance with 1/0 of the transmission data, or the polarity of the applied voltage is reversed.

  A connector 18 is connected to the secondary side of the pulse transformer 17, and is connected to the communication path 30 via the connector 18. Data (palace train) having the same contents as the transmission data (palace train) input to the primary side of the pulse transformer 17 appears on the secondary side, and the appearing data is sent to the communication path 30 via the connector 18. Is output. The data (palace train) received via the connector 18 is given to the secondary side of the pulse transformer 17, and the same data as the data given to the secondary side appears on the primary side, and the transceiver 16 Given to. Thereby, the data can be transferred while the internal circuit of the master 10 and the communication path 30 side are cut off in a DC manner by the pulse transformer 17.

  FIG. 4 is a diagram illustrating an internal configuration of the slave 20. As shown in the figure, the slave 20 includes an I / O interface unit 21, an operation / display unit 23, and a physical layer circuit 24.

  The I / O interface unit 21 is an interface unit that exchanges data with devices connected to the outside such as sensors and actuators. The I / O interface unit 21 connects the external devices and exchanges data with the INPUT / OUTPUT circuit 21a and slave communication. ASIC 21b, nonvolatile memory 21c, and unit power supply unit 21d. The nonvolatile memory 21c stores an abnormality history, a unit (slave) profile, and the like. The unit power supply 21 d receives a DC 25 V power supply from the outside, steps down the voltage to 5 V and 3.3 V, which are voltages used in the slave 20, and supplies them to a predetermined circuit or the like in the slave 20. The slave communication ASIC 21b acquires the output signal from the external device (input device) acquired from the INPUT / OUTPUT circuit 21a, encodes it, creates transmission data, and sends it to the physical layer circuit 24. 24. Data that can be understood by the external device is generated from the data acquired via the data 24 and is provided to the external device (output device) connected to the INPUT / OUTPUT circuit 21a.

  The operation / display unit 23 includes a number setting switch 23a for setting the unit number of the unit (slave 20), an LED 23b as a display means, a mode setting switch 23c for setting various modes, and a connection node number setting / transmission speed. It has a dip switch 23d for performing various settings such as switching setting / communication mode setting. The number setting switch 23a and the mode setting switch 23c can be constituted by a rotary switch or the like. The LED 23b includes a single color indicator lamp, a 7 segment LED, and the like.

  The physical layer circuit 24 includes a transceiver 26, a pulse transformer 27, and a connector 28. The transceiver 26 is arranged between the slave communication ASIC 21b and the primary side of the pulse transformer 27, and outputs transmission data received from the communication ASIC 21b at a predetermined timing. That is, ON / OFF of energization is controlled for the primary side of the pulse transformer 27 in accordance with 1/0 of the transmission data, or the polarity of the applied voltage is reversed.

  A connector 28 is connected to the secondary side of the pulse transformer 27, and is connected to the communication path 30 via the connector 28. Data (palace train) having the same contents as the transmission data (palace train) input to the primary side of the pulse transformer 27 appears on the secondary side, and the appearing data passes through the connector 28 to the communication path 30. Is output. The data (palace train) received via the connector 28 is given to the secondary side of the pulse transformer 27. Data having the same contents as the data given to the secondary side appears on the primary side, and the transceiver 26 Given to. Thereby, the data can be transferred while the pulse transformer 27 cuts off the internal circuit of the master 10 and the communication path 30 side in a DC manner.

  In the present invention, as shown in FIG. 5, a midpoint M is provided on the side of the transceivers 16 and 26 (primary side) of the pulse transformers 17 and 27, and the midpoint M is connected to the power supply ground. Furthermore, in this example, the pulse transformers 17 and 27 on the master side and the slave side are set to be the same. That is, the number of turns on the primary side: secondary side of the pulse transformers 17 and 27 was set to N01: N02. In FIG. 5, the node address of the master 10 is set to # 00, and the node address of the slave 20 is set to # 01.

  Next, the operation of the present embodiment will be described. FIG. 5 shows an energization state and a voltage generated when data is transmitted from the master 10 of the node # 00 to the slave 20 of the node # 01. Here, the port A of the transceivers 16 and 26 is a high output, the port B is a low output, the voltage appearing between the ports AB of the node # 00 is V01, and the voltage appearing between the ports AB of the node # 01 Is V3, the voltage appearing on the communication path 30 is V00, and the primary and secondary turns of the pulse transformers 16 and 26 are N01 and N02.

  When the master 10 on the transmission side performs high output, the current output from the port A reaches the primary winding of the pulse transformer 16 and flows through the path from the midpoint M of the primary winding to the power supply ground. Therefore, the number of turns of the winding portion through which current actually flows is half of N01. Then, when a current flows through the primary side winding, a voltage is generated between both terminals of the secondary side winding of the pulse transformer 17 as shown in FIG. Since current flows through the entire winding on the secondary side, the substantial transformation ratio at the time of transmission is “N02 / (N01 / 2)”.

Therefore, when the output voltage V01 is applied between the A port of the transceiver 16 and the ground, the voltage V00 appearing on the secondary side of the pulse transformer 17, that is, the communication path 30, is
V00 = {N02 · (N01 · 2)} × V01
= 2 · (N02 / N01) × V01
It becomes.

  On the other hand, the voltage V00 is applied to the secondary side of the pulse transformer 27 of the slave 20 on the receiving side, and a current flows through the entire secondary winding. Then, a voltage V03 is generated between both terminals of the primary winding of the pulse transformer 27, and the voltage V03 is applied between the AB ports of the transceiver 26. At the time of reception, since there is no influence of the midpoint, the transformation ratio of the pulse transformer 26 is “N02 / N01”.

Therefore, the secondary side of the pulse transformer 27 of the slave 20 on the receiving side, that is, the reception voltage V03 of the transceiver 26 is
V03 = (N01 / N02) × V00
= (N01 / N02) × {2 · (N02 · N01) × V01}
= 2 · V01
It becomes.

  In the above example, the case of transmitting from the master 10 side has been described, but the same applies to the case of transmitting data from the slave 20 side. Therefore, assuming that there is no loss in the communication path and each component, the output voltage on the transmission side appears as a double voltage on the reception side regardless of the transformation ratio of the pulse transformers 17 and 27. Therefore, in the present embodiment, by using the midpoint connection, the transmission / reception performance can be doubled as compared with the case where communication is performed using a conventional pulse transformer without the midpoint connection.

  In other words, in the present embodiment, when the same transmission medium (cable) as that in the prior art is used for the communication path 30, the transmission distance is doubled. In addition, when using the same communication distance as in the past, a transmission medium that is disadvantageous in terms of communication with a wave attenuation up to twice that of the transmission medium used in the communication path can be used. The range of cable selection is greatly expanded.

  Further, since it is considered that the transformation ratio of the pulse transformers 17 and 27 is not related to the peak value of transmission and reception, the characteristic impedance of the communication path and the apparent impedance of the physical layer circuits 16 and 26 during transmission can be changed by changing the transformation ratio. It is possible to prevent deterioration in transmission quality due to matching and double reflection of the reflected wave from the receiving side and superimposition on the traveling wave.

Impedance matching is
Z01 / Z00 = (N01 / N02) 2
What is necessary is just to set so that it may satisfy | fill.

Therefore, when N01 = 1, N02 = (Z00 / Z01) 1/2
It is possible to achieve consistency by setting

  The primary windings of the pulse transformers 17 and 27 (the windings connected to the transceivers 16 and 26) are connected at the midpoint, so that the number of turns N02 of the secondary winding is higher than that of the primary winding N01. Even if it is small, the output voltage V00 of the pulse transformers 17 and 27 is higher than the output voltages V01 and V02 of the transmitting-side transceiver unless at least N02 is less than or equal to half of N01. Therefore, even if the transformation ratio of the pulse transformer is adjusted to achieve impedance matching, the voltage applied to the communication path 30 is suppressed from becoming extremely low, and the range in which impedance matching can be achieved is widened.

  Therefore, even if a transmission medium whose impedance is not matched with that at the time of transceiver transmission is used while improving the transmission / reception performance, it is possible to prevent a reduction in transmission quality due to reflected wave superposition due to impedance mismatch.

  FIG. 6 shows a main part of another embodiment of the present invention. In this example, between the port A of the transceivers 16 and 26 and the pulse transformers 17 and 27, between the port B of the transceivers 16 and 26 and the pulse transformers 17 and 27, and the midpoint of the primary winding of the pulse transformers 17 and 27 Current limiting resistors R1, R2, and R4 are arranged in series between M and the power supply ground, respectively. As a result, the value of the current flowing through the physical layer circuits 14 and 24 during transmission can be reduced.

  In other words, in the present embodiment, since the midpoint M is dropped to the power supply ground, assuming that the parameters such as the components used, the number of turns, and the input power are the same as those of the conventional configuration shown in FIG. The current flowing through the current is doubled. Therefore, the current value is reduced by inserting current limiting resistors R1, R2, and R4 in series on the circuit that flows during transmission. The specific resistance value of each current limiting resistor R1, R2, R4 is set so that the current value is optimal or satisfies the specifications.

  Furthermore, in this embodiment, the terminating resistor R3 is connected between both terminals of the primary windings of the pulse transformers 17 and 27. The resistance value of the termination resistor R3 is sufficiently larger than the resistance values of the current limiting resistors R1 and R2. Accordingly, when the physical layer circuits 14 and 24 are viewed from the outside, the rear side of the termination resistor R3 is terminated without being seen. By disposing the device on which the termination resistor R3 is mounted on the termination side of the main communication path 30 or the sub communication path 32, the termination resistor 33 can be omitted.

  Although FIG. 6 shows an example in which the current limiting resistors R1, R2, and R4 and the termination resistor R3 are both mounted, it is of course possible to mount either one. In addition, slaves 20 and masters 10 constituting the network may have different specifications. That is, for example, a circuit having a physical layer circuit on which current limiting resistors R1, R2, and R4 are mounted and a device having a physical layer circuit on which current limiting resistors R1, R2, and R4 are not mounted can be mixed.

  FIG. 7 shows an example of another network system to which the present invention is applied. In this example, a repeater 40 having a waveform shaping function is provided instead of the T-branch 31 in the network configuration shown in FIG. 2 to extend the transmission distance. FIG. 8 is a block diagram showing the internal configuration of the repeater 40. As shown in this figure, the repeater 40 has a pulse transformer 41 and a transceiver 42 arranged in series on the input / output side, and a waveform shaping ASIC 43 arranged between the transceivers 42 on the input / output side. The waveform shaping ASIC 43 is for correcting a signal having a distorted waveform that has been transmitted into a signal having a pulse train without distortion. The transceiver 42 and the waveform shaping ASIC 43 can basically be conventional ones. In the pulse transformer 41, the middle point M of the winding on the transceiver 43 side is dropped to the power supply ground in the same manner as in each of the above-described embodiments.

  As a result, the repeater 40 can achieve the same effects as the slave 20 described above, and can further extend the transmission distance or expand the range of usable transmission media. Further, it is more preferable to arrange the current limiting resistors R1, R2, and R4 at appropriate positions of the pulse transformer 41.

It is a figure which shows a prior art example. It is a figure which shows an example of a network system. It is a block diagram which shows an example of the internal structure of a master. It is a block diagram which shows an example of the internal structure of a slave. It is a figure which shows the principal part of suitable one Embodiment of this invention. It is a figure which shows the principal part of another suitable embodiment of this invention. It is a figure which shows the other example of a network system. It is a block diagram which shows an example of an internal structure of a repeater.

Explanation of symbols

10 Master 11 PLC Bus Interface Unit 12 MPU Unit 13 Operation / Display Unit 14 Physical Layer Circuit 15 Communication ASIC
16 Transceiver 17 Pulse transformer 18 Connector 20 Slave 21 I / O interface unit 23 Operation / display unit 24 Physical layer circuit 26 Transceiver 27 Pulse transformer 28 Connector 30 Main communication path (communication path)
31 T branching device 32 Sub communication path (communication path)
33 Terminating resistor 40 Repeater 41 Pulse transformer 42 Transceiver 43 Waveform shaping ASIC

Claims (7)

A serial communication device that performs data communication with another serial communication device via a communication path and uses a transceiver and a pulse transformer in a physical layer circuit connected to the communication path,
The winding on the communication path side of the pulse transformer is connected to the communication path, the winding on the transceiver side is connected to the transceiver, and the communication path side and the transceiver side are disconnected in a direct current manner.
A communication device, wherein a midpoint is provided in a winding on the transceiver side of the pulse transformer, and the midpoint is connected to a power supply ground.   The communication device according to claim 1, wherein a current suppression resistor is provided in series with a line connecting the transceiver and the pulse transformer and a line connecting the midpoint and the power supply ground.   The communication device according to claim 1, wherein the communication device is a master unit configuring a programmable controller or a slave or a repeater connected to the master unit via a network.   4. The communication device according to claim 1, wherein the transformation ratio of the pulse transformer is set so that impedance matching is established with a connected communication path. 5. One port A of the transceiver is a high output and the other port B is a low output,
When the transmission voltage appearing between the ports A and B is V01, the voltage appearing on the communication path to which the secondary side of the pulse transformer is connected is V00, and the number of turns on the primary and secondary sides of the pulse transformer is N01 and N02 In addition,
When the transceiver outputs high, the current output from the port A reaches the primary winding of the pulse transformer and flows through a path from the midpoint of the primary winding to the power supply ground.
When a current flows through the primary winding, a voltage of 2 × (N02 / N01) × V01 is generated between both terminals of the secondary winding of the pulse transformer, and the voltage appears on the communication path. The communication apparatus according to any one of claims 1 to 3, wherein the communication apparatus is set to be V00. A communication device that receives a signal output from another communication device according to claim 5,
The reception voltage applied between one port A and the other port B of the transceiver is V03, the voltage appearing on the communication path to which the secondary side of the pulse transformer is connected is V00, and the primary side and secondary side of the pulse transformer When the number of turns is N01 and N02,
When a voltage V00 (= 2 × (N02 / N01) × V01) of the communication path is applied to the secondary side of the pulse transformer and a current flows through the entire secondary winding, the primary winding of the pulse transformer A voltage V03 generated between both terminals of the line is applied as a reception voltage between the AB ports of the transceiver,
The reception voltage V03 of the transceiver is
V03 = (N01 / N02) × V00
= (N01 / N02) × {2 · (N02 · N01) × V01}
= 2 ・ V01
The communication device according to claim 1, wherein the communication device is set to be In a network system having a plurality of nodes connected via a communication path,
A network system, wherein the node is mounted with the communication device according to any one of claims 1 to 6.

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