JPH0746210A - Multiplex transmission system - Google Patents

Abstract

PURPOSE:To obtain the multiplex transmission system in which the transmission reliability is high, the transmission speed is fast, number of transmission lines is less and a short-circuit of the transmission line is simply detected. CONSTITUTION:A transmitter 12 sends a transmission signal TS in the voltage mode in which '0', '1' of transmission data are expressed by a narrower and a wider pulse width complementary data are respectively added just after transmission data, and a start synchronizing signal is added to its head. A data discrimination section 60 of a receiver 14 uses an up-down counter to discriminate whether the data are '0' or '1', a complementarity check section 62 checks the complementarity between transmission data and their complementary data and uses a switch circuit 66 to return a reply signal RS in the current mode for a start synchronization period in a succeeding communication cycle when the complementarity is all normal. A reply discrimination section 32 in the transmitter 12 monitors a voltage V1 across a resistor 36 to detect the return of the reply signal RS and then a short-circuit of a transmission line 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiplex transmission system used for wiring reduction in factories, plants and the like.

[0002]

2. Description of the Related Art A schematic example of a conventional multiplex transmission system is shown in FIG.
Shown in. In this multiplex transmission system, a plurality of data input in parallel to the transmitting device 2 are converted into serial data and transmitted to the receiving device 4 via one transmission line 6, and the receiving device 4 receives the received serial data. Is converted in parallel and output. The transmission line 6 includes a signal line 7 for signal transmission and a ground line 8 for ground.

In a conventional multiplex transmission system of this type, a baseband system for transmitting a pulse waveform as it is is used as a transmission system for transmitting "0" or "1" data.

As a data representation method, conventionally, as shown in FIG. 9, for example, "1" is set depending on the presence or absence of a pulse.
Alternatively, a method of expressing "0" data is adopted.

In addition, a multiplexing method for transmitting a plurality of data using one transmission line 6 mainly includes a frequency division method and a time division method, but this type is used because of low cost. The time-division system is usually adopted in the system for wire saving.

A sum check method is adopted as an error detection method for detecting a transmission error due to the influence of disturbance such as noise. In this method, for example, as shown in FIG. 10, after a series of data, sum check data representing the sum A of the series of data is added, such data is transmitted from the transmitting side, and the receiving side This is a method in which the sum of a series of received data is compared with the sum check data (A in this example), and if both match, it is determined to be normal, and if they are different, it is determined to be an error.

Further, in this kind of multiplex transmission system, there is a case where a method of confirming whether or not the transmission was normal is adopted in order to improve the reliability of the transmission. A transmission line for reply signal return different from the signal line 7 is wired between the transmission device 2 and the reception device 4, and reception is normally performed from the reception device 4 to the transmission device 2 using this transmission line. The reply signal indicating that it was was sent back. This is a conventional transmission signal and a reply signal which are produced by changing both voltages. When two such signals are placed on one signal line 7, the two signals influence each other and the waveform is distorted. This is because, for example, it becomes impossible to distinguish both signals.

A conventional communication frame structure for returning a reply signal is, for example, as shown in FIG.
In addition to the synchronization period and the data transmission / input / output period, a reply confirmation period for confirming the return of the reply signal is provided.

[0009]

However, the conventional multiplex transmission system as described above has many problems as follows.

A transmission method that expresses “1” or “0” data depending on the presence or absence of a pulse is adopted. Since this method has an extremely high dependence on the peak value of the transmission waveform, fluctuations in power supply voltage, noise, etc. A transmission error is apt to occur due to the disturbance due to, and thus the transmission reliability is low.

Since the sum check method is adopted as the transmission error detection method, the transmission error detection capability is low and the detection thereof is slow. More specifically, the sum check method may not be able to detect a transmission error when a plurality of data are inverted due to the influence of disturbance. For example, as shown in FIG. 11, when two data (data 0 and data n in this example) are inverted due to the influence of disturbance, the sum of a series of data received on the receiving side is the sum of normal ( That is, since it is the same as A), such a transmission error cannot be detected. Therefore, the reliability of transmission is low. The low reliability of transmission is especially serious in a severe noise environment such as a factory. In addition, in the above sum check method, even if a transmission error occurs during the transmission of a series of data, the transmission side must detect the transmission error until the time when the sum of the series of data and the sum check data are compared. Therefore, there is also a problem that transmission error detection is slow.

In the reply signal confirmation method as described above, as can be seen from FIG. 12, the transmission time becomes longer because the reply confirmation period must be provided.
Transmission speed decreases. Further, since the transmission line for the reply signal has to be provided, the number of transmission lines increases, and the material, the wiring man-hour and the cost increase.

When a signal is transmitted by changing the voltage as described above, the transmission line 6, more specifically, the signal line 7 thereof.
When the ground line 8 and the ground line 8 are short-circuited due to an accident, miswiring, or the like, an overcurrent flows through the transmission line 6, thereby destroying the circuit that sends a signal to the transmission line 6. In order to prevent this, there is a method of inserting a current limiting resistor or the like in the signal line 7 in series, but if this is done, the voltage drop of the transmission line 6 will be large even during normal operation, Another problem such as a short communication range occurs. There is also a method in which a short-circuit detection circuit for detecting a short circuit in the transmission path 6 is provided and the protection operation is performed in response to the detection of the short circuit.
In the case of this method, since a short circuit detection circuit must be provided, the circuit becomes complicated and the cost increases.

Therefore, according to the present invention, the reliability of transmission is high,
The transmission speed is high and the number of transmission lines is small,
Further, it is a main object to provide a multiplex transmission system capable of easily detecting a short circuit of a transmission line.

[0015]

SUMMARY OF THE INVENTION To explain the outline of the present invention, in the present invention, in a transmission signal transmitted from a transmitting device, whether transmission data is "0" or "1" is expressed by the length of a pulse width. In this method, since the dependence of the transmission waveform on the peak value is low, a transmission error is unlikely to occur due to fluctuations in the power supply voltage or disturbance such as noise. Therefore, the reliability of transmission is high.

Further, according to the present invention, in the receiving device,
The up / down counter is used to judge whether the received data is "0" or "1". According to this method, it is correctly judged whether the data is "0" or "1" even if some disturbance is added. Therefore, it is resistant to disturbance due to noise or the like, and the reliability of transmission is improved from this viewpoint as well.

Further, according to the present invention, one transmission data and complementary data of which the value is inverted are continuously transmitted from the transmitting device, and when the influence of the disturbance occurs,
Normally, only one of the two pieces of data is inverted and the complementarity is lost. Therefore, by checking the complementarity between the two pieces of data in the receiving device, a transmission error can be reliably detected. Therefore, since the error capture rate when affected by the disturbance is improved, the reliability of transmission is increased from this viewpoint as well.

Further, according to the present invention, in the receiving device,
Every time one transmission data and its complementary data are received, the complementarity between the two data is checked, so the error detection time is extremely short when affected by disturbance, and quick detection is possible. is there.

Further, in the present invention, the reply signal indicating that the reception is normal is returned from the receiving device in the current mode, and whether or not the transmission is normal is transmitted depending on the presence or absence of the reply signal. Since it can be confirmed on the device side, the reliability of transmission is improved from this point of view as well, and since a transmission line dedicated to the reply signal is not required, it is possible to realize wire saving, wire saving man-hours and cost saving. .

Further, according to the present invention, since the reply signal is returned at the same timing as the start synchronization signal, a special period for returning the reply signal is unnecessary. as a result,
The transmission time can be shortened and the transmission speed can be improved.

Further, the transmitting device determines whether or not the current mode signal is returned during the period other than the transmission period of the start synchronizing signal, thereby also serving as the circuit for detecting the reply signal. In other words, it is possible to easily detect a short circuit in the transmission line without providing a dedicated short circuit detection circuit. As a result, the size of the device can be reduced and the cost can be reduced by simplifying the circuit. Also,
Since it is not necessary to insert a current limiting resistor or the like in series with the transmission line for short-circuit protection, the communicable distance does not become short.

[0022]

1 is a block diagram showing a multiplex transmission system according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a transmission signal waveform, a reply signal waveform, and a return signal waveform when the transmission line is short-circuited in the multiplex transmission system of FIG.

This multiplex transmission system has a plurality of input terminals 20 and transmits a plurality of pieces of transmission data corresponding to the input signals input to the respective input terminals 20 in series and included in a transmission signal TS for transmission. 12 and a plurality of output terminals 50, receives the transmission signal TS sent from the transmitter 12, converts serial transmission data contained therein into parallel, and outputs a signal corresponding to the transmission data. The receiving device 14 that outputs from each output terminal 50, and the transmission line 16 that connects the transmitting device 12 and the receiving device 14 are provided. The transmission line 16 is composed of a signal line 17 for signal transmission and a ground line 18 for ground.

The transmitter 12 is, in this example, an input circuit 2
2, output circuit 24, control circuit 26 connected to them,
The control circuit 26 includes a changeover switch circuit 34, a power supply terminal 40, a resistor 36 connected between the changeover switch circuit 34, and an amplifier 38 having an input portion connected to both ends of the resistor 36.

The input circuit 22 is a circuit for an input interface, and in this example, an on / off signal at (n + 1) points is input from the input terminal 20. The output circuit 24 is a circuit for an interface for outputting an alarm signal S ₂ given from a reply determination unit 32 described later to the output terminal 21.

In this example, the control circuit 26 includes a transmission control section 28 which constitutes a transmission control means and a reply judgment section 32 which constitutes a reply judgment means.

The transmission control unit 28 converts the transmission data provided in parallel from the input circuit 22 into serial data, and determines whether each transmission data is "0" or "1" depending on the length of the pulse width. I, which represents the start sync signal for synchronization and I / O for adding and complementing complementary data whose value is inverted immediately after each transmission data and before and after the series of data. Each / O service period is added to create a transmission control signal S ₁ which is a source of the transmission signal TS as shown in FIG. 2A and cyclically outputs it. The transmission signal TS of FIG. 2A will be further described later.

The changeover switch circuit 34 constitutes a changeover switch means, and in response to the transmission control signal S ₁ from the transmission control section 28, the common terminal c is selectively set between the terminal a and the terminal b side. To switch to. A signal line 17 of the transmission line 16 is connected to the common terminal c, a resistor 36 is connected to the terminal a, and a ground line 18 is connected to the terminal b.

In the changeover switch circuit 34, when the common terminal c is switched to the terminal a side, a voltage is applied from the power supply terminal 40 through the resistor 36, so that the voltage of the common terminal c becomes "H" level, When it is switched to the b side, it is connected to the ground, so that the voltage of the common terminal c becomes "L" level. In this way, the changeover switch circuit 34 outputs the transmission signal TS as shown in FIG. 2A in the voltage mode to the transmission line 16 under the control of the transmission control unit 28. When the transmission control signal S ₁ from the transmission control unit 28 is interrupted, the changeover switch circuit 34 remains in the state in which the common terminal c is switched to the terminal b side. This changeover switch circuit 3
4 is composed of, for example, a combination of a plurality of transistors.

The reply determination section 32 monitors the voltage V ₁ across the resistor 36 via the amplifier 38 to detect the voltage V ₁ concerned.
Is not higher than a predetermined value during the transmission period of the start synchronization signal in the transmission signal TS, it is determined that the transmission in the previous communication cycle is abnormal and the alarm signal S ₂ is output. Furthermore, if the voltage V ₁ rises above a predetermined value during a period other than the transmission period of the start synchronization signal, the transmission line 16
Is determined to be short-circuited, the alarm signal S ₂ is output, and the output of the transmission control signal S ₁ from the transmission control unit 28 is interrupted. When the alarm signal S ₂ is output from the reply determination unit 32, the alarm signal S ₂ is output via the output circuit 24 to the output terminal 21.
Is output from.

Explaining the transmission signal TS shown in FIG. 2A, the one cyclic frame has a start synchronization signal for synchronization and a series of data 0 to 0 following it.
n, followed by an I / O service period. The I / O service period is a period for processing the next input on the transmitting side and processing the output on the receiving side. T is a period for one data, for example, 120μ
s.

In this multiplex transmission system, also referring to FIG. 3A, when transmitting one transmission data of "0" or "1", complementary data of which the value is inverted is added immediately after each transmission data. Then, each transmission data and its complementary data are paired and continuously transmitted.

Further, in this multiplex transmission system, whether the data is "0" or "1" is expressed by the length of the pulse width (that is, by pulse width modulation). That is,
Referring also to FIG. 3A, a combination of an “L” level of 30 μs and a subsequent “H” level of 90 μs represents “0”, and a combination of an “L” level of 60 μs and a subsequent “H” level of 60 μs indicates “0”. 1 ”is represented. One cycle is 120 μs. This representation method is common to transmission data and complementary data.

In this example, the receiver 14 has an amplifier 64 whose input section is connected to the signal line 17 and the ground line 18 of the transmission line 16, and a control circuit 56 connected to this amplifier 64.
And an output circuit 52 connected to the control circuit 56. Further, between the signal line 17 and the ground line 18, a switch circuit 66 including a resistor 67 and a transistor 68 connected in series is connected, which constitutes a switch means.

The power source terminal 70 of the receiving device 14 and the power source terminal 40 of the transmitting device 12 may be connected to different power sources or one common power source.

The amplifier 64 amplifies the transmission signal TS sent via the transmission line 16 and supplies it to the control circuit 56.

In this example, the control circuit 56 includes a reception control unit 58 which constitutes a reception control unit, a data determination unit 60 which constitutes a data determination unit, and a complementation checking unit 62 which constitutes a complementation checking unit. ing.

An example of the operation of the data judging section 60 will be described with reference to FIG. 3. The data judging section 60 includes an up / down counter, and at a fixed timing, in this example, at each falling edge of the signal. Sampling of the signal is started and this sampling is performed for a certain period T ₂ (60 in this example).
μs) Continue until the judgment point. In the meantime, in the up / down counter, if the sampling data is “L” level, it is counted up in this example, and if it is “H” level, it is counted down. Therefore, the count value is shown in FIG.
As shown in (1), when the data is "0", it starts to increase and then decreases halfway, and when the data is "1", it increases steadily.

Then, at the judgment point, the count value at that time is compared with a fixed threshold value. In this example, the threshold value is set to an intermediate value between the count value when the data is “0” and the count value when the data is “1”. Then, when the count value at the determination point is smaller than the threshold value, "0" is determined, and when the count value is larger than the threshold value, "1" is determined.

FIG. 4 shows a more specific example of the configuration of the data determination unit 60 as described above. In this example, the data determination unit 6
0 includes a sampling circuit 601, an up / down counter 602, and a comparison circuit 603.

The sampling circuit 601 receives a signal as shown in FIG. 3A, samples the signal at a constant period during the period T ₂ , and if the sampled value is at the "L" level, for example, outputs a "0" pulse. If it is at "H" level, "1" pulse is output.

In this example, the up-down counter 602 counts up if the pulse given from the sampling circuit 601 is "0", down-counts if it is "1", and outputs the count value.

The comparison circuit 603 compares the count value given from the up / down counter 602 with a constant threshold value as described above, and when the count value at the determination point as described above is smaller than the threshold value. Output "0",
When it is large, "1" is output. This output is the determination result of the input data.

Returning to FIG. 1, the reception control unit 58 converts each transmission data serially supplied from the data determination unit 60 into parallel data to create output data, and supplies the output data to the output circuit 52. In addition, in this embodiment, the reception control unit 58 is
It has a function of controlling the entire receiving device 14, for example, the control shown in the flow of FIG. 7.

The output circuit 52 is a circuit for an output interface, and outputs an output signal to each output terminal 50 based on the output data given from the reception controller 58. Further, the alarm signal given from the reception controller 58 is output to the output terminal 51.

The complementarity check unit 62 includes a data decision unit 6
Every time 0 to 1 transmission data and the following complementary data are given, the complementarity between the two data (that is, one is “0”)
If so, check that the other is "1", and only when the complementarity is established for all the transmission data in one communication cycle, during the reception period of the start synchronization signal in the next communication cycle. The reception normal signal S ₃ is output to. Further, in this example, if there is even one data set for which complementarity is not established, a reception abnormality signal is output to the reception control unit 58.

The switch circuit 66 includes a complementary check unit 6
In response to the reception normal signal S ₃ given from 2, the resistance value between the signal line 17 and the ground line 18 of the transmission line 16 is reduced, and thereby the current mode reply signal RS as shown in FIG. 2B is obtained. It is generated in the transmission line 16.

More specifically, the reception normal signal S ₃
Is during the start sync signal reception period (from the transmission side,
The changeover switch circuit 34 is switched to the terminal a side and is applied during the transmission period of the start synchronizing signal, whereby the transistor 68 is turned on. When the transistor 68 is turned on, the resistor 67 is connected between the signal line 17 and the ground line 18, and the power supply terminal 40 on the transmitter 12 side is connected.
A current larger than usual (for example, about 10 times the normal current) flows through the path from the resistor 36, the changeover switch circuit 34, the signal line 17, and the resistor 67. This current is the reply signal RS in the current mode, and in this way,
The reply signal RS can be returned from the receiver 14 to the transmitter 12 in current mode.

Note that, for example, the reception control unit 58 determines whether the received transmission signal TS is not disturbed and the basic frame as shown in FIG. 2A is established, and whether it is established, The reception normal signal S is set on the condition that the respective transmission data have complementarity.
₃ may be given to the switch circuit 66 to return the reply signal RS.

In the transmitter 12, as described above, the voltage V ₁ across the resistor 36 is monitored by the reply determination section 32 via the amplifier 38, and when the reply signal RS is returned, this resistance is detected. Since a large amount of current flows through 36 and the voltage V ₁ across it rises above normal, this voltage V 1
It is possible to determine whether or not the transmission in the immediately preceding communication cycle was normal by monitoring by the reply determination unit 32 whether or not the increase of ₁ is in the transmission period of the start synchronization signal.

Further, when the transmission line 16 is normal, the current mode signal is not returned to the transmitter 12 side except during the transmission period of the start synchronization signal, and the transmission line 16 is short-circuited. When the signal line 17 and the ground line 18 are short-circuited, the current mode signal is always returned during the transmission period of the transmission signal TS (however, in FIG. 2C, This is an example of the case where the transmission is not interrupted, and if the transmission of the transmission signal TS is interrupted according to the present invention, the current mode signal disappears at that time). This means that a large amount of current flows through the resistor 36 and the voltage V ₁ across the resistor 36 rises higher than usual. Therefore, a circuit for confirming the return of the reply signal RS (more specifically, the resistor 36, The amplifier 38 and the reply determination unit 32) are also used, and the determination time of the voltage V ₁ in the reply determination unit 32 is simply switched to other than during the transmission period of the start synchronization signal, that is, during the transmission period of the start synchronization signal. V
By determining whether or not there is a rise of ₁ , the short circuit of the transmission line 16 can be easily detected.

As described above, in this multiplex transmission system,
In the transmission signal TS transmitted from the transmission device 12, the transmission data is expressed as "0" or "1" depending on the length of the pulse width. Since this method has a low dependence on the peak value of the transmission waveform, , Transmission errors are less likely to occur due to fluctuations in power supply voltage and disturbances such as noise. Therefore, the reliability of transmission is high.

Further, in the data judging section 60 of the receiving device 14, the received data is "0" by using the up / down counter.
Or "1" is determined, and when doing so, the count value at the determination point by the up / down counter may fluctuate somewhat when disturbance such as noise is added during the sampling period. Maybe, but
The overall trend of the count value is the same as when there is no disturbance.

For example, as shown in FIG. 5, when a disturbance that causes a part of the signal to go to the "L" level or a disturbance that causes a part of the signal to go to the "H" level is applied, the middle of the sampling period Although the count value slightly increases and decreases, and the count value at the determination point also fluctuates somewhat accordingly, the overall tendency of the count value is the same as that in the case without the disturbance in FIG.

Therefore, by comparing the count value with the threshold value, it is possible to correctly determine whether the data is "0" or "1" even if some disturbance is applied. Therefore, it is resistant to disturbance due to noise or the like, and the reliability of transmission is improved from this viewpoint as well.

Contrary to the above embodiment, if the signal sampling value is "L" level, the up / down counter may down-count, and if it is "H" level, up-counting may be performed. In such a case, the count value and the threshold value may be considered by vertically inverting with respect to the 0 level line as the axis of symmetry in FIGS. 3B and 5B.

In addition, in this multiplex transmission system, one data and complementary data whose value is inverted are continuously transmitted from the transmitter 12, and when the influence of disturbance causes both data to be transmitted. It is extremely rare to invert both, and normally, only one of the two data is inverted and the complementarity is lost. Therefore, the complementarity check unit 62 of the receiving device 14 checks the complementarity between the two data. As a result, it is possible to reliably detect a transmission error. Therefore, since the error capture rate when affected by the disturbance is improved, the reliability of transmission is increased from this viewpoint as well.

In addition, since the complementarity checking unit 62 checks the complementarity between both data each time one data and its complementary data are received, the time until an error is detected in the case of being affected by disturbance. Is very short, and quick detection is possible.

Further, in this multiplex transmission system, the reply signal RS indicating that the reception is normal is returned from the receiving device 14 in the current mode, and the transmission is normal depending on the presence or absence of the reply signal RS. Since it is possible to confirm whether or not the transmission has occurred, the transmission reliability is improved from this viewpoint as well.

Moreover, since the transmission signal TS is transmitted in the voltage mode and the reply signal RS is returned in the current mode, both signals can be discriminated even if both signals are put on one signal line 17, and therefore one signal is transmitted. The signal line 17 can be shared for transmission of both signals. That is, since the transmission line dedicated to the reply signal is not required, it is possible to realize wiring saving, wire saving man-hours and cost saving.

Moreover, since the reply signal RS is returned at the same timing as the start synchronization signal, a special period for returning the reply signal becomes unnecessary. As a result, the transmission time can be shortened and the transmission speed can be improved.

Further, whether or not the current mode signal is returned during the period other than the transmission period of the start synchronization signal is determined by the reply determination section 32 of the transmission device 12, whereby the reply signal is detected. Double as a dedicated circuit, that is, easily without providing a dedicated short-circuit detection circuit,
A short circuit of the transmission line 16 can be detected and short circuit protection can be performed. As a result, the size of the device can be reduced and the cost can be reduced by simplifying the circuit. Further, since it is not necessary to insert a current limiting resistor or the like in series with the signal line 17 for short-circuit protection, the communicable distance does not become short.

FIG. 6 is a flow chart showing an example of the overall operation on the transmission device 12 side. On the transmission device 12 side, the transmission signal TS is transmitted for each communication cycle, and the return signal is monitored during the transmission period to determine whether the transmission was normal and whether the transmission path 16 is short-circuited. Is constantly monitored. The processing contents of each processing step in this figure are as described above.

FIG. 7 is a flowchart showing an example of the overall operation of the receiving device 14 side. In the receiving device 14, in this figure, the return of the reply signal RS is not immediately interrupted due to the reception abnormality of one communication cycle, and 2
In the case of reception abnormality up to the communication cycle, the reply signal RS is returned and the previous data is output as it is, and only when the reception is abnormal for three communication cycles or more, the alarm is output to the output terminal 51 and the reply signal RS is output. Is interrupted and the abnormality is notified to the transmitting device 12 side. The other processing contents of each processing step in this figure are as described above. In this way, in the case of a temporary communication abnormality, the alarm is not output on the transmitting device 12 side and the receiving device 14 side, and the immediately preceding output data is output as it is. Easy to use. However, doing so is preferred but not essential.

[0065]

As described above, according to the present invention, in the transmission signal transmitted from the transmitting device, whether the transmission data is "0" or "1" is expressed by the length of the pulse width. Has a low dependence on the peak value of the transmission waveform, and therefore transmission errors are less likely to occur due to fluctuations in the power supply voltage and disturbances such as noise. Therefore, the reliability of transmission is increased.

Further, according to the present invention, in the receiving device,
The up / down counter is used to judge whether the received data is "0" or "1". According to this method, it is correctly judged whether the data is "0" or "1" even if some disturbance is added. can do. Therefore, it is resistant to disturbance due to noise or the like, and the reliability of transmission is improved from this viewpoint as well.

Further, according to the present invention, one transmission data and complementary data of which the value is inverted are continuously transmitted from the transmission device, and when the influence of disturbance causes
Normally, only one of the two pieces of data is inverted and the complementarity is lost. Therefore, by checking the complementarity between the two pieces of data in the receiving device, a transmission error can be reliably detected. Therefore, since the error capture rate when affected by the disturbance is improved, the reliability of transmission is increased from this viewpoint as well.

Further, according to the present invention, in the receiving device,
Every time one transmission data and its complementary data are received, the complementarity between the two data is checked, so the error detection time is extremely short when affected by disturbance, and quick detection is possible. is there.

Further, in the present invention, the reply signal indicating that the reception is normal is returned from the receiving device in the current mode, and whether or not the transmission is normal is transmitted depending on the presence or absence of the reply signal. Since it can be confirmed on the device side, the reliability of transmission is improved also from this viewpoint.

As described above, in the present invention, since the means for improving the reliability of transmission are taken multiple times, the reliability of transmission becomes extremely high. Therefore, the multiplex transmission system of the present invention exerts a particularly remarkable effect in use in a severe noise environment such as a factory.

Moreover, since one transmission line can be shared for returning the reply signal and transmitting the transmission signal, a transmission line dedicated to the reply signal is not required, and wiring saving, man-hour saving and cost saving are realized. can do.

Further, according to the present invention, since the reply signal is returned at the same timing as the start synchronizing signal, a special period for returning the reply signal becomes unnecessary. as a result,
The transmission time can be shortened and the transmission speed can be improved.

Further, the transmitter side determines whether or not the current mode signal is returned during the period other than the transmission period of the start synchronization signal, and thereby also serves as the circuit for detecting the reply signal. In other words, it is possible to easily detect a short circuit in the transmission line without providing a dedicated short circuit detection circuit. As a result, the size of the device can be reduced and the cost can be reduced by simplifying the circuit. Also,
Since it is not necessary to insert a current limiting resistor or the like in series with the transmission line for short-circuit protection, the communicable distance does not become short.

[Brief description of drawings]

FIG. 1 is a block diagram showing a multiplex transmission system according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a transmission signal waveform, a reply signal waveform, and a return signal waveform when the transmission line is short-circuited in the multiplex transmission system of FIG.

FIG. 3 is a diagram illustrating an example of a data determination method in a data determination unit in FIG.

FIG. 4 is a block diagram illustrating a more specific configuration example of a data determination unit in FIG.

5 is a diagram showing an example in the case where a disturbance is added in the data determination method in the data determination unit in FIG.

FIG. 6 is a flowchart showing an example of the overall operation of the transmitting device side in FIG.

FIG. 7 is a flowchart showing an example of the overall operation on the receiving device side in FIG.

FIG. 8 is a schematic diagram showing an example of a conventional multiplex transmission system.

FIG. 9 is a schematic diagram showing a conventional data representation method based on the presence or absence of a pulse.

FIG. 10 is a schematic diagram showing an example of a transmission signal of a conventional sum check system.

11 is a schematic diagram showing an example of a case where a disturbance is added to the transmission signal of FIG.

FIG. 12 is a schematic diagram showing an example of a conventional frame configuration when returning a reply signal.

[Explanation of symbols]

 12 transmitter 14 receiver 16 transmission line 17 signal line 18 ground line 20 input terminal 26 control circuit 28 transmission control unit 32 reply determination unit 34 changeover switch circuit 36 resistance 50 output terminal 56 control circuit 58 reception control unit 60 data determination unit 62 Complementarity check unit 66 switch circuit

Claims (1)

[Claims] 1. A transmitter having a plurality of input terminals, which transmits a plurality of transmission data corresponding to a signal input to each input terminal in series and including the transmission data, and a plurality of output terminals. A receiving device that has a transmission signal sent from the transmission device, converts serial transmission data included in the transmission signal to parallel, and outputs a signal corresponding to the transmission data from each output terminal, A multiplex transmission system comprising a transmission path connecting between a transmission device and a reception device, wherein the transmission device converts transmission data given in parallel to serial data, and each transmission data is converted depending on the length of the pulse width. A start synchronization signal for expressing "0" or "1", further adding complementary data with its value inverted immediately after each transmission data, and for synchronizing before and after the series of data. And for processing the input and output I /
In response to the transmission control signal given from the transmission control means, which adds the O service period, creates a transmission control signal which is a source of the transmission signal, and cyclically outputs the transmission control signal, The signal line forming the transmission line is selectively switched to and connected to the other end side of the resistor having one end connected to a power supply terminal and the ground line side forming the transmission line, thereby connecting the transmission line to the transmission line. A changeover switch means for outputting a transmission signal in a voltage mode and a voltage across the resistor are monitored, and if the voltage does not rise above a predetermined value during a transmission period of a start synchronizing signal in the transmission signal, an alarm signal Is output, and if the voltage rises above a predetermined value during a period other than the transmission period of the start synchronization signal, an alarm signal is output and the output of the transmission control signal from the transmission control means is interrupted. The reception device includes a sampling unit, an up / down counter, and a comparison unit, and starts sampling a signal at a constant timing for each transmission data and each complementary data in the transmission signal. If the sampled value is "L" level, the up / down counter counts in one direction, and if it is "H" level, it counts in the opposite direction. Data count means for comparing the count value with a fixed threshold value and judging whether the data is "0" or "1" according to the magnitude of both values, and transmission data serially given from the data judgment means are connected in parallel. The reception control means for converting and outputting, one transmission data from the data judging means and the complementary data following it. Each time and are given, the complementarity between both data is checked, and only when the complementarity is established for all the transmission data in one communication cycle, during the start synchronization signal reception period in the next communication cycle. A complementary check means for outputting a reception normal signal, and a signal connected to the signal line and the ground line forming the transmission line, and receiving a signal from the complementary check means in response to the signal. And a switch means for reducing a resistance value between the line and the ground line to generate a current-mode reply signal in the transmission line.