JP4875882B2 - Communication device, communication system - Google Patents

Description

  The present invention relates to a communication device that transmits data using a voltage between signal lines, and more particularly to a signal transmission method.

  Data handled by a communication device such as a computer is represented by binary codes of 0 and 1. Various transmission methods have been devised in order to transmit the data represented by 0 or 1 between communication devices. As an example, there is a method in which 0 and 1 are transmitted through two signal lines in association with pulse waveforms “present” and “none”. This transmission method is largely divided into a single flow method and a double flow method. Divided into two.

The single flow method is a method of expressing 0 and 1 with or without voltage. For example, 0 is expressed as zero volts, and 1 is expressed as 5 volts.
However, in the single-flow method, 0 and 1 are expressed with and without voltage, so when signal transmission is repeated, charges gradually accumulate in the signal line, and the charge accumulated in the signal line generates a potential difference. By doing so, there is a problem of adversely affecting signal transmission. Since the longer the signal transmission distance, the higher the possibility of being adversely affected by charge accumulation, it is difficult to perform stable signal transmission in the long-distance communication in the single-flow method.

On the other hand, the double flow method refers to a method of expressing 0 and 1 by the difference in voltage polarity. For example, double flow RZ (Return to Zero) is widely known as a double flow transmission method. The double flow RZ is, for example, 0 when the voltage polarity is negative and 1 when the voltage polarity is positive. In the double flow RZ, the polarity of the voltage is switched according to the data to be transmitted. Therefore, compared to the single flow method, it is advantageous for transmission of signals over a long distance.
New edition of Electrical and Electronic Glossary 1st edition 1st edition September 1, 1988 Published by Ohm Co., Ltd.

However, even if the transmission method using the double flow method is used, if the data to be transmitted may be the same continuously, the polarity of the voltage is not switched during that time, and the electric charge is gradually accumulated in the signal line. May adversely affect communications.
Accordingly, an object of the present invention is to provide a communication apparatus, a communication method, and a communication system that enable stable long-distance communication even when data to be transmitted continuously becomes the same. And

  In order to solve the above-described problems, the present invention is a communication device that controls supply of one output voltage output from a constant voltage power source and transmits a signal using two signal lines. A polarity inverting unit for inverting the polarity of the output voltage supplied to the signal line, a switching unit for switching on / off of the supply of the output voltage, and in synchronization with a clock of a fixed period according to the value of data to be transmitted. A supply control unit that controls the switching by the switching unit, and an inversion control unit that controls the polarity inversion unit so as to periodically perform the inversion every predetermined clock regardless of the value of data to be transmitted. Features.

A communication apparatus having the above-described configuration controls on / off of voltage supply according to data to be transmitted, and inverts the polarity of the supplied voltage regardless of the data to be transmitted.
As a result, even when the data to be transmitted continuously become the same, the polarity of the voltage supplied to the signal line is periodically inverted by the inversion control unit, so that the charge is accumulated in the signal line. It can be avoided.

Therefore, it is possible to reduce the adverse effect on the signal due to the accumulation of electric charges in the signal line, and it is possible to stably transmit a signal over a long distance compared to the conventional case.
By the way, in signal transmission, the ease of synchronization between communication devices is also an important factor. This is because if the synchronization cannot be easily established, the communication device on the data receiving side cannot determine the content of the received data at an early stage, and it is difficult to perform high-speed communication.

  In order to facilitate the establishment of synchronization while avoiding charge accumulation, a transmission system that converts 1 bit of a signal into a 2-bit code, such as the Manchester code system, is conventionally used. For example, in the Manchester encoding method, 0 is set to minus 5 volts, 1 is set to plus 5 volts, data to be transmitted “0” is expressed as “01” using a 2-bit bandwidth, and data to be transmitted is “1”. Is represented by “10” using a 2-bit bandwidth. As a result, when transmitting 1-bit information using a 2-bit bandwidth, the polarity is always reversed, so that no signal is lost and synchronization is easily established.

An AMI (Alternate Mark Inversion) code system (bipolar code system) is also widely used. The AMI code method is a method in which, for example, 0 is expressed with a voltage, 1 is expressed without a voltage, and the polarity of the voltage is alternately changed between plus and minus each time 0 is transmitted.
However, in the case of the Manchester code system, the probability of synchronization is easy, but 1-bit information is transmitted using a 2-bit bandwidth, and there is a problem that transmission efficiency is deteriorated. In addition, in the case of AMI code, if data expressed with voltage is continuous, the polarity is inverted every time 1 bit is transmitted, so it is easy to establish synchronization, but it can be expressed without voltage. When there is continuous data, there is a problem in that it is difficult to establish synchronization because no signal state continues.

Therefore, the supply control unit controls whether the supply to one signal line is kept on or switched from the on state to off within one clock according to the value of data to be transmitted. It is good.
As a result, regardless of the value of the data to be transmitted, the voltage supplied to the signal line is in an on state at the start of transmission of 0 or 1. Further, the polarity of the voltage supplied to the signal line is periodically reversed. Therefore, the communication device on the data receiving side synchronizes by using the timing at which the polarity of the voltage is periodically switched when the same data is continuously received in both 0 and 1 data. Can be easily established. In addition, since data is expressed depending on whether the voltage remains on or off, no extra bandwidth is required to transmit 1-bit information.

Therefore, even if any data of 0 and 1 is continuous without increasing the bandwidth, it is possible to easily establish synchronization while stabilizing transmission of a long-distance signal.
In addition, each time the supply control unit transmits data for a predetermined bit, the switching is performed so that data obtained by bit-inversion of the data value for the predetermined bit is transmitted following the data for the predetermined bit. It is good also as controlling.

As a result, when the communication device is operating normally, the bit-inverted data is transmitted after the transmitted data, so when the communication device hardware always transmits the same bit due to a failure or the like. It becomes easy to detect a failure or the like.
A second communication device that receives a predetermined voltage and performs two-way communication with the communication device via the two signal lines, according to a value of data transmitted by the second communication device; Within one clock, a transmission control unit may be provided for controlling whether or not a short-circuit signal of a predetermined ampere is applied to each signal line.

The second communication device sends a short-circuit signal having a predetermined amperage to the signal line connected to the communication device with the communication destination according to the data transmitted by the second communication device. As a result, the current flowing through the signal line changes.
The communication destination communication device can detect the content of data transmitted by the second communication device by detecting a change in the current flowing through the signal line.

Thereby, bi-directional communication can be performed between two communication apparatuses using two signal lines.
A communication method used in a communication apparatus that controls supply of one output voltage output from a constant voltage power source and transmits signals using two signal lines, the two signal lines being connected to each other. In the polarity inversion step for inverting the polarity of the output voltage to be supplied, the switching step for switching on / off the supply of the output voltage, and the switching step in synchronization with a clock of a certain period according to the value of data to be transmitted Communication comprising: a supply control step for controlling the switching; and an inversion control step for controlling to periodically perform the inversion in the polarity inversion step every predetermined clock regardless of the value of data to be transmitted. It is good also as a method.

By using the communication method described above, long-distance communication can be performed stably.
A first communication device that controls the supply of one output voltage output from a constant-voltage power supply and transmits signals using two signal lines; and a first communication device that performs bidirectional communication with the first communication device. A communication system comprising two communication devices, wherein the first communication device turns on / off the supply of the output voltage, and a polarity reversing unit that reverses the polarity of the output voltage supplied to the two signal lines. A switching unit that switches, a supply control unit that controls the switching by the switching unit in synchronization with a clock of a certain period, and a value that is transmitted at each predetermined clock regardless of the value of the data that is transmitted An inversion control unit that controls the polarity inversion unit so as to perform inversion periodically, and the second communication device, within one clock, according to the value of data transmitted to the first communication device, For each signal line A transmission control unit configured to control whether or not to send a constant ampere short-circuit signal, wherein the first communication device detects that a current supplied to each signal line has changed by a predetermined value or more; The communication system may further include means for receiving data transmitted by the second communication device.

  By the above-described communication system, bidirectional communication can be performed stably.

<Embodiment>
DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a communication apparatus and a communication system according to the present invention will be specifically described with reference to the drawings.
<Overview>
The communication system includes a master device and a slave device. Each of the master device and the slave device is a communication device, and is connected via two signal lines.

A communication protocol used by the communication system is a frame synchronization / bit synchronization method.
Pulse width modulation is used for signal transmission from the master device to the slave device, and current change caused by applying a short-circuit signal of a predetermined amperage is used for signal transmission from the slave device to the master device.
The feature of the present invention is that when the master device transmits a signal to the slave device, the signal line is periodically synchronized with the clock regardless of whether the content of the signal to be transmitted is 0 or 1. It is in the point which switches the polarity of the voltage supplied to.

This makes it easy to establish synchronization and realize long-distance transmission regardless of the contents of the signal to be transmitted.
<Configuration>
FIG. 1 is a functional block diagram of the master device 1000 and the slave device 2000.
As shown in the figure, a master device 1000 connected to a power source 1 that is a DC power source includes a polarity inversion unit 101, a switching unit 102, a timing generation unit 103, a received data extraction unit 104, and a control unit 105. It consists of.

The master device 1000 is connected to the slave device 2000 via the D + signal line 31 and the D− signal line 32.
The polarity inversion unit 101 is a circuit that inverts the polarity of the supply voltage supplied to the D + signal line 31 and the D− signal line 32 according to control by the control unit 105.
The switching unit 102 is a switch circuit that switches on and off the supply voltage supplied to the D + signal line 31 and the D− signal line 32 according to control by the control unit 105.

The timing generation unit 103 is a clock generation circuit that supplies a clock to the polarity inversion unit 101, the switching unit 102, and the like.
The reception data extraction unit 104 detects that the current supplied to each signal line is changed by a predetermined value or more by the short circuit signal sent from the slave device 2000 in synchronization with the clock, and detects the slave device 2000. It is a circuit that detects that a signal is transmitted from and extracts data indicated by the transmitted signal. The extracted data is output to the control unit 105.

  The control unit 105 is a control circuit that controls the operation of the master device 1000, and controls communication with the slave device 2000. The polarity inversion unit 101 is controlled to periodically invert the polarity of the supply voltage supplied to the D + signal line 31 and the D− signal line 32 in synchronization with the clock generated by the timing generation unit 103. Further, the switching unit 102 is controlled in accordance with data transmitted to the slave device 2000 to control on / off of the voltage supplied to each signal line. In addition, it receives the data extracted by the received data extraction unit 104 and performs bidirectional communication with the slave device 2000.

In addition to this, the master device 1000 includes a display unit and an operation unit (not shown), displays the state of the device, detection of an abnormality, and the like on the display unit, and accepts user operations via the operation unit.
The slave device 2000 is connected to the master device 1000 via the D + signal line 31 and the D− signal line 32.

As shown in the figure, the slave device 2000 includes a receiving unit 201, a transmitting unit 202, and a control unit 203.
The receiving unit 201 includes a clock synchronization unit that extracts a clock based on a signal, detects a voltage difference between the D + signal line 31 and the D− signal line 32, and is transmitted from the master device 1000 to the slave device 2000. A circuit for extracting data. When the voltage supplied to the D + signal line 31 is higher than the D− signal line 32 by a predetermined voltage or more, the voltage difference is detected as positive, and the voltage supplied to the D + signal line 31 is higher than the D− signal line 32. If the voltage is lower than a predetermined voltage, the voltage difference is detected as negative. If the difference in voltage supplied to each signal line is substantially equal and there is no difference greater than a predetermined voltage, the voltage difference is detected as zero. The detection result is output to the control unit 203.

The transmission unit 202 changes the current flowing through each signal line by applying a short-circuit signal of a predetermined ampere, such as 150 mA, to each signal line according to the control by the control unit 203 to change the current flowing through each signal line. Is a circuit for transmitting data.
The control unit 203 is a control circuit that controls the operation of the slave device 2000 and controls communication with the master device 1000. The clock extracted by the receiving unit 201 is received. Further, the detection result of the voltage difference of each signal line is received from the receiving unit 201, and the data transmitted from the master device 1000 to the slave device 2000 is extracted. Further, the transmitter 202 is controlled to perform bidirectional communication with the master device 1000 in synchronization with the clock.

In addition, the master device 1000 and the slave device 2000 receive power from a constant voltage power source separately from the power source 1 and operate each control unit 105 and the like.
<Circuit diagram>
Here, an example of specific circuit configurations of the master device 1000 and the slave device 2000 will be described.

FIG. 2 is a diagram illustrating a circuit configuration of the master device 1000.
As shown in the figure, the master device 1000 includes a control circuit 111, a timing generation circuit 112, and a transmission control circuit 113.
The control circuit 111 controls communication with the slave device 2000. Data to be transmitted to the slave device 2000 is determined, and the data is transmitted via the transmission control circuit 113 in accordance with the clock generated by the timing generation circuit 112. Further, a change in the current supplied to the signal line is detected, and data transmitted by the slave device 2000 is extracted.

The timing generation circuit 112 generates a clock having a predetermined period.
The transmission control circuit 113 controls the operation of the transistors 114, 115, 116, and 117 via the transistor control lines 124, 125, 126, and 127 according to data to be transmitted.
When described in comparison with the functional block diagram of FIG. 1, the control circuit 111 corresponds to the received data extraction unit 104 and the control unit 105 of FIG. The timing generation circuit 112 corresponds to the timing generation unit 103. The transmission control circuit 113 and the transistors 114 to 117 correspond to the polarity inversion unit 101 and the switching unit 102.

In addition, the polarity of the voltage supplied to each signal line is periodically inverted in synchronization with the control by the transmission control circuit 113, and the on / off of the voltage supplied to each signal line is switched according to the data to be transmitted. The relationship with the operation will be described later.
FIG. 3 is a diagram illustrating a circuit configuration of the slave device 2000.
As shown in the figure, the slave device 2000 includes a control circuit 211 and a transmission / reception control circuit 212.

The control circuit 211 controls communication with the master device 1000. The data transmitted by the master device 1000 is received from the transmission / reception control circuit 212 and processed. Data to be transmitted to the master device 1000 is determined, and data is transmitted via the transmission / reception control circuit 212 according to a predetermined clock.
The transmission / reception control circuit 212 is connected to the transistors 213, 214, 215, and 216 via transistor control lines 223, 224, and 225. A current is passed through the transistor control line 225 in accordance with data transmitted to the master device 1000. Further, the voltage difference between the signal lines is extracted via the transistor control lines 223 and 224, the data transmitted by the master device 1000 is received, the transmission data is extracted, and is output to the control circuit 211. In the example shown in the figure, data when the voltage difference is positive is detected via the transistor control line 223, and data when the voltage difference is negative is detected via the transistor control line 224. Further, a voltage difference of zero is detected via the transistor control line 223 and the transistor control line 224.

When described in comparison with the functional block diagram of FIG. 1, the control circuit 211 corresponds to the control unit 203. The transmission / reception control circuit 212 and the transistors 213 to 216 correspond to the reception unit 201 and the transmission unit 202.
As shown in FIG. 2, the power supply 1 supplies a voltage of 24 V to the master device 1000 and each signal line. The control circuit 111, the timing generation circuit 112, and the transmission control circuit 113 are supplied with a voltage of 5V.

As shown in FIG. 3, a voltage of 5 V is supplied to the control circuit 211 and the transmission / reception control circuit 212 of the slave device 2000.
<Transmission method>
(Frame data structure)
Next, a signal transmission method will be described.

FIG. 4 is a diagram illustrating a configuration of frame data used when the master device 1000 and the slave device 2000 perform communication.
As shown in the figure, the frame structure of one frame is composed of a start bit 41, a preamble bit 42, an I / O bit 43, an I / O end bit 44, an ID bit 45, and a frame end bit 46. Become.

The start bit 41 indicates the start of one frame.
The preamble bit 42 indicates that the I / O bit 43 follows.
The I / O bit 43 indicates the content of data transmitted / received between the master device 1000 and the slave device 2000.
The I / O end bit 44 indicates the end of the I / O bit 43.

The ID bit 45 indicates the frame ID.
The frame end bit 46 indicates the end of one frame.
The start bit 41 has a Hi level for a predetermined bit. The preamble bit 42, the I / O end bit 44, and the frame end bit 46 have the same bit width, and the Lo level is set to a predetermined bit. For example, the start bit 41 is 9 bits, and the preamble bit 42 is 3 bits.
(Pulse waveform)
FIG. 5 is a diagram illustrating a pulse waveform used when the master device 1000 and the slave device 2000 perform communication. The control unit 105 of the master device 1000 transmits a pulse waveform including transmission data in the I / O bit. The example in the figure shows a pulse waveform in the I / O bit. The master device 1000 inverts the voltage supplied to the D + signal line 31 and the D− signal line 32 every time 1-bit data is transmitted in one clock.

Whether a 1-bit pulse waveform indicates 0 or 1 is expressed by whether or not there is a voltage shift. That is, 0 if the voltage remains on, and 1 if the voltage turns off after half a clock from the voltage on state.
The address 51 indicates the address of data transmitted between the master device and the slave device. One address includes 2-bit information.

A waveform 52 indicates a pulse waveform. The portion indicated by hatching indicates that a current change occurs when the slave device 2000 places a short-circuit signal on each signal line.
The master transmission data 53 indicates data that the master device 1000 transmits to the slave device 2000.
The slave transmission data 54 indicates data that the slave device 2000 transmits to the master device 1000.

Master transistor control line 55 indicates ON / OFF of transistor control lines 124 to 127 controlled by the transmission control circuit of master device 1000.
The slave transistor control line 56 indicates ON / OFF of the transistor control line 225 controlled by the transmission / reception circuit of the slave device 2000.
In the figure, when each transistor control line is on, it is indicated as ◯, and when it is off, it is indicated as x.

  In addition, the master device 1000 and the slave device 2000 transmit and receive data using a complementary bit verification method. The complementary bit verification method is a transmission method in which data to be transmitted is made redundant to improve the error detection rate, and includes one bit of transmission data and one bit of data obtained by inverting the bit of the transmission data. 1 address. That is, when 0 is transmitted, 1 is transmitted after 0. For example, if the data is binary code 4 bits “1” “0” “0” “1”, that is, 1001, the bit-inverted data is transmitted every time each bit is transmitted. The transmission data is “10” “01” “01” “10”, that is, 10010110.

  In the example shown in the figure, the data transmitted from the master device 1000 to the slave device 2000 has the same value continuously in the portions where the addresses of the data to be transmitted are 4 and 5. That is, 0 is continuous in the portion where the address is 4, and 1 is continuous in the portion where the address is 5. At this time, the slave device 2000 can detect that there is an error in the transmission data in the portions where the addresses are 4 and 5. Similarly, the data transmitted from the slave device 2000 to the master device 1000 is the same continuously in the portions where the addresses are 6 and 7, and the master device 1000 includes the slave device 2000 in the portions where the addresses are 6 and 7. It is possible to detect that there is an error in the data transmitted by.

<Operation>
(Master device 1000)
Next, the operation of the master device 1000 will be described.
FIG. 6 is a flowchart showing the operation of the master device 1000.
As shown in the figure, when determining the content of data to be transmitted to slave device 2000 (step S61), control unit 105 of master device 1000 generates frame data by adding complementary bits, preamble bits, and the like. (Step S62).

  When the frame data is generated, the polarity inversion unit 101 and the switching unit 102 are controlled according to the clock supplied by the timing generation unit 103 to transmit the frame data to the slave device 2000. During transmission of frame data (step S64: NO), the transmission data of the slave device 2000 extracted by the reception data extraction unit 104 is received and processed (step S63).

When the transmission of the frame data is finished (step S64: YES), the transmission data transmission process is started again (step S61).
(Slave device 2000)
Next, the operation of the slave device 2000 will be described.
FIG. 7 is a flowchart showing the operation of the slave device 2000.

  The control unit 203 of the slave device 2000 waits until the start bit and the preamble bit are input (step S71: NO). When the start bit and the preamble bit are detected (step S71: YES), the control unit 203 based on the start bit and the preamble bit. Frame synchronization is performed, and bit synchronization is performed using the timing at which the polarity of the voltage is switched after reception of the preamble bit. If the voltage is positive or negative after the half clock has elapsed after bit synchronization, the transmission data of the master device 1000 is accepted as 0, and if the voltage is zero after the half clock has elapsed, the transmission data of the master device 1000 is accepted as 1. Every time one bit is received, the process from bit synchronization to determination of transmission data of the master device 1000 is repeated. Further, after receiving the preamble bits, the transmitting unit 202 is controlled to the master apparatus 1000 to transmit data using the complementary bit collation method (step S72).

When the reception of the frame data is finished (step S73: YES), the reception of the frame data and the data transmission process to the master device 1000 are repeated again (step S71).
<Supplement>
As described above, the communication device and the communication system according to the present invention have been described based on the embodiments. However, the present invention can be modified as follows, and the present invention is not limited to the above-described embodiments. is there.
(1) In the above-described embodiment, the polarity is inverted every clock. However, the present invention is not limited to this, and the polarity may be inverted every predetermined clock, for example, every 8 clocks.
(2) In the above-described embodiment, the supply voltage supplied to either the D + signal line 31 or the D− signal line 32 may be switched on and off. Further, the switching unit 102 may be provided between the power source 1 and the polarity inversion unit 102.
(3) In the above-described embodiment, the voltage supplied to the master device 1000 or the like is 24V or 5V, but is not limited thereto. The circuit configuration is not limited to the above example. For example, the circuit configuration of the master device 1000 may be as shown in FIG. 8, and the circuit configuration of the slave device 2000 may be as shown in FIG.
(4) In the above-described embodiment, the master device 1000 has been described as communicating with one slave device 2000. However, as shown in FIG. 10, a plurality of slave devices 2000 (2000a, 2000, 2000b,...) And communicating. For example, it can be used in a communication system that manages a plurality of devices such as a factory production line, a plant, and a physical distribution management system. In order to manage a plurality of devices, for example, each address of transmission data indicated by an address 51 in FIG. 4 may be assigned to each device to be managed. The device to be managed receives the data transmitted from the master device 1000 by extracting the data of the address portion of the own device. In addition, data can be transmitted to the master device 1000 by passing a current through the address portion of the device itself. Thereby, a wiring-saving communication system can be realized. In addition, communication between a plurality of master devices 1000 or a communication system including a plurality of master devices 1000 and a plurality of slave devices 2000 may be used.
(5) In the above-described embodiment, a single power source 1 is used to supply a voltage to each signal line. However, the present invention is not limited to this. Further, although the power source 1 has been described as being supplied from the outside of the master device 1000, it may be inside the master device 1000.
(6) In the above-described embodiment, in order to express whether the data to be transmitted is 0 or 1, transmission is performed depending on whether there is a voltage difference or zero after a half clock has elapsed since the bit synchronization. The value of the data to be determined is determined, but it is not necessary to be limited to after half a clock, and the method of expressing the data depending on whether there is a voltage difference is not limited to this, and other methods may be used. .
(7) In the above-described embodiment, the complementary bit verification method is used. However, the complementary bit verification method is not necessarily used, and another bit verification method may be used. Also, as shown in FIG. 4, one frame is composed of a start bit and the like, but the frame configuration is not limited to this form.
(8) A part or all of the constituent elements constituting each of the above devices may be configured by one system LSI (Large Scale Integration). The system LSI is an ultra-multifunctional LSI manufactured by integrating a plurality of components on a single chip, and specifically, a computer system including a microprocessor, ROM, RAM, and the like. . A computer program is stored in the RAM. The system LSI achieves its functions by the microprocessor operating according to the computer program.
(9) The above embodiment and the above modifications may be combined respectively. (10) The present invention may be the method described above.

  The present invention is used as a communication network such as a LAN (Local Area Network), a communication system, and a device management apparatus such as a factory or facility.

The functional block diagram of the master apparatus 1000 and the slave apparatus 2000. The figure which shows the circuit structure of the master apparatus 1000. The figure which shows the circuit structure of the slave apparatus 2000. FIG. The figure which shows the structure of the frame data used when the master apparatus 1000 and the slave apparatus 2000 communicate. The figure which shows the pulse waveform used when the master apparatus 1000 and the slave apparatus 2000 communicate. 6 is a flowchart showing the operation of the master device 1000. 5 is a flowchart showing the operation of the slave device 2000. The figure which shows the circuit structure of the master apparatus 1000. The figure which shows the circuit structure of the slave apparatus 2000. FIG. The figure which shows a communication system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply 101 Polarity inversion part 102 Switching part 103 Timing generation part 104 Reception data extraction part 105 Control part 201 Reception part 202 Transmission part 203 Control part 31 D + signal line 32 D- signal line 111 Control circuit 112 Timing generation circuit 113 Transmission control circuit 211 control circuit 212 transmission / reception control circuit

Claims (4)

A communication device that controls the supply of one output voltage output from a constant voltage power source and transmits signals using two signal lines,
A polarity inversion unit for inverting the polarity of the output voltage supplied to the two signal lines;
A switching unit for switching on and off the supply of the output voltage;
According to the value of data to be transmitted, a supply control unit that controls the switching by the switching unit in synchronization with a clock of a fixed period;
Regardless of the value of data to be transmitted, an inversion control unit that controls the polarity inversion unit so as to periodically perform the inversion every predetermined clock ,
The supply control unit controls whether the supply to one signal line is kept on or switched from an on state to off within one clock according to a value of data to be transmitted. A communication device. The supply control unit controls the switching so as to transmit data obtained by bit-inversion of the data value of the predetermined bit every time data of the predetermined bit is transmitted following the data of the predetermined bit. The communication device according to claim 1, wherein: A communication method used in a communication apparatus that controls supply of one output voltage output from a constant voltage power source and transmits a signal using two signal lines,
A polarity inversion step of inverting the polarity of the output voltage supplied to the two signal lines;
A switching step of switching on and off the supply of the output voltage;
A supply control step for controlling the switching in the switching step in synchronization with a clock of a certain period according to the value of data to be transmitted;
Irrespective of the value of the data to be transmitted, viewed contains an inverting control step of controlling the inverted periodically performed as in the polarity inversion step every predetermined clock,
The supply control step controls whether the supply to one signal line is maintained in an on state or switched from an on state to off in one clock according to a value of data to be transmitted. Communication method. A first communication device that controls supply of one output voltage output from a constant voltage power source and transmits signals using two signal lines, and a second communication that performs bidirectional communication with the first communication device A communication system comprising a device,
The first communication device is
A polarity inversion unit for inverting the polarity of the output voltage supplied to the two signal lines;
A switching unit for switching on and off the supply of the output voltage;
According to the value of data to be transmitted, a supply control unit that controls the switching by the switching unit in synchronization with a clock of a fixed period;
Regardless of the value of data to be transmitted, an inversion control unit that controls the polarity inversion unit so as to periodically perform the inversion every predetermined clock,
The supply control unit controls whether the supply to one signal line is kept on or switched from an on state to off in one clock according to a value of data to be transmitted,
The second communication device is
In accordance with the value of data transmitted to the first communication device, a transmission control unit that controls whether or not to send a short-circuit signal of a predetermined ampere to each signal line within one clock,
The first communication device includes means for receiving data transmitted by the second communication device by detecting that a current supplied to each signal line has changed by a predetermined value or more. Communication system.

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