JPH0342823B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a bidirectional transmission system in which a master station and a slave station are coupled by a pulse transformer and a single bidirectional transmission line to perform bidirectional data transmission. More specifically, the master station includes a DC power supply and a switch circuit connected in series to the master station winding of the pulse transformer.
The slave station is provided with a means for receiving the transmission signal from the slave station and obtaining a master station side reception signal by comparing the current flowing through the winding with a reference value, The present invention relates to a bidirectional transmission system comprising an impedance variable means connected in parallel to a master station, and a means for receiving a transmission signal sent from a master station and obtaining a slave station reception signal.

[Conventional technology and problems]

Generally, the presence or absence of data, that is, data “1”,
In digital transmission of signals for "0" information, high quality transmission is required, and economic requirements such as saving on transmission lines must also be met. For this purpose, a bidirectional transmission system using a single line is being considered. In the above method, it is necessary to be able to detect a disconnection or no connection in the transmission line, but according to the conventional technology, a complicated circuit and a complicated procedure are required to detect the disconnection or no connection in the transmission line. There were many products that required the following, which resulted in high costs and the lack of suitable products.

As an example of this type of bidirectional transmission system,
-71349 and JP-A-56-117456 are known. In these known systems, it is not possible to know the status of the secondary side (slave station side) of the pulse transformer from the transmitting/receiving circuit on the master station side, that is, it is not possible to know whether the transmission line is disconnected or not connected. However, if a disconnection or non-connection detecting means were to be provided to remedy this drawback, it would be expensive.

[Purpose of the invention]

The present invention eliminates the drawbacks of the prior art mentioned above,
A simple circuit is added to the transmitting/receiving circuit on the master station side, and through simple processing, it is possible to detect a disconnection or no connection in the transmission line.This detection information can be used to determine whether the received data is valid or invalid, and can also be known as RAS information. The purpose is to provide an economical bi-directional transmission system that can be used.

[Key points of the invention]

In order to achieve the above object, the present invention bidirectionally transmits signals using a single transmission line coupled via a pulse transformer included in both or one of transmitting/receiving circuits on the master station side and slave station side. , on the parent station side,
Switching means is connected in series to the master station winding of the pulse transformer, and when a transmission signal or a synchronization signal from the master station is sent to the slave station, the switching means opens and closes in response to the signal. The slave station includes a transmitting means, and a receiving means for receiving a transmission signal from the slave station by detecting the current flowing in the master station winding of the pulse transformer and comparing it with a reference value. impedance variable means connected in parallel between slave station windings of the transformer; receiving means for receiving a transmission signal and a synchronization signal from the master station generated in the slave station windings of the pulse transformer; The impedance is variable in a first period included in the synchronization signal transmission period in order to transmit one of the transmission signals by controlling the transmission timing of the transmission signal from the slave station based on the synchronization signal from the station side. and transmitting means for changing the impedance of the means,
When the transmission line is in a normal state and the impedance of the variable impedance means is changed and when the impedance is not changed during the transmission period of the synchronization signal, the intermediate value of the two received signals detected by the receiving means on the master station side is determined. setting the reference value;
The receiving means on the master station side samples the received signal in the first period and a second period other than the first period in the sending period of the synchronization signal, and compares the received signal with the reference value, and The method is characterized in that the validity of the comparison result of the received signal detected in the first period is determined based on the comparison result of the received signal detected in the first period.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. In the figure, 100 is the master station side transmitting/receiving circuit, 20
0 is the slave station side transmitting/receiving circuit.

Data circuits 1 and 2 are connected to the master station side transmitting/receiving circuit 100, data circuits 12 and 13 are connected to the slave station side transmitting/receiving circuit 200, and both transmitting/receiving circuits 100 and 200 are connected to pulse transformers 5 and 8.
are coupled via a single signal transmission line 7.

On the master station side, a DC power supply Vcc is connected to a master station winding (primary winding P) of a pulse transformer 5 via a resistor 4.

The master station transmission signal or synchronization signal Sm from the data circuit 2 opens and closes the switching circuit 6 and drives the pulse transformer 5.

In this embodiment, as a means for receiving the transmission signal Ss from the slave station and obtaining the master station reception signal Rm by comparing the current flowing through the master station winding P of the pulse transformer 5 with a reference value, , resistance 4, reference voltage
It has a comparator 3 to which Vref is applied.
That is, the value of the current flowing through the winding is converted into a voltage drop across the resistor 4 and provided to the comparator 3. Comparator 3 converts the above voltage into the reference voltage.
It compares it with Vref, and sends out an output H when it falls below the reference voltage Vref. The output of the comparator 3 becomes the master station side received signal Rm. And this signal Rm
is branched and inputted to a received data detection circuit 22 and a transmission line state detection circuit 23 to perform data detection and transmission line state detection, and the detection results are inputted to the data circuit 1.

Note that 21 is a data sampling clock generating circuit which sends out first and second sampling clocks CL ₁ and CL ₂ having different timings (phases) as will be described later.

On the slave station side, the secondary winding S of the pulse transformer 8 of the slave station side transmitting/receiving circuit 200 is connected to the transmission line 7,
One end of the child station side winding (primary winding P) is grounded, and the other end is connected to a received signal detection circuit 10 and a switching circuit 9 constituting an impedance variable means. The output of the received signal detection circuit 10 is input to the data circuit 12 as the slave station side reception signal Rs, and data is detected.The signal Rs is also input to the timing setting circuit 11, where the timing is controlled and the slave station side control output signal is generated. Data circuit 13 as Cs
control. By controlling this control output signal Cs,
A slave station transmission signal Ss is sent from the data circuit 13 at a predetermined timing. The control signal input terminal of the switching circuit 9 is connected to the data circuit 13, receives the slave station side transmission signal Ss sent out from the data circuit 13, and is thereby switched (ON/OFF controlled). When the switching circuit 9 is on, the impedance of the pulse transformer 8 seen from the master station side is small, and the switching circuit 9
When is off, the above impedance becomes large. In this way, the switching circuit 9 functions as an impedance variable means.

Now, in Fig. 1, direction A (from the master station to the slave station)
Data signal transmission in the B direction (from the slave station to the master station) is in the "receiving mode".
shall be.

FIG. 2 is a time chart of signals in the "transmission mode" of the embodiment of FIG.

In Fig. 2, a is the waveform of the transmission data Dsm sent from the master station to the slave station, b is the waveform of the master station transmission signal Sm, c is the waveform of the slave station reception signal Rs, and d is the slave station transmission signal Ss. This is the waveform of

The master station side transmission signal Sm shown in FIG. 2b corresponds to the data “1” and “0” of the master station side transmission data Dsm,
It is a signal that has undergone pulse width modulation, and this signal Sm
As a result, the switching circuit 6 repeats opening and closing operations according to the pulse width of the signal. The pulse transformer 5 is driven by the operation of the switching circuit 6, and the master station transmission signal Sm is sent to the transmission line 7, thereby driving the slave station pulse transformer. The response generated by driving the pulse transformer 8 on the slave side is extracted from the winding P on the slave side of the pulse transformer 8 and detected by the received signal detection circuit 10.
As shown in FIG. 2c, a slave station reception signal Rs having a waveform corresponding to the master station transmission signal Sm is output.

In this case, appropriate circuit constants are set so that the pulse width modulation waveform is transmitted correctly. That is, as shown in FIG. 2a and b, a time slot with a time width τ is assigned to a 1-bit signal corresponding to one piece of data, and in this time slot, a large time slot is assigned to the data "1". A pulse with a width ta is assigned, and a pulse with a small time width tb is assigned to data "0".

Although there is a delay time due to transmission, the slave station side received signal Rs is a faithful reproduction of this pulse width modulated signal Sm, as shown in FIG. 2c. Therefore, the slave station side data circuit 12 transmits the master station transmission data.
DSM can be easily played.

In the transmission mode, as shown in FIG. 2d, the slave station transmission signal Ss is kept low, and the switch circuit 9 is closed (ON).

Next, the operation in reception mode will be explained. FIG. 3 is a time chart of signals in the "reception mode" of the embodiment of FIG. In Fig. 3, a is the waveform of the master station side transmission signal Sm, b is the waveform of the slave station reception signal Rs, c is the waveform of the transmission data Dss sent from the slave station to the master station, and d is the waveform of the slave station side transmission. The waveform of the signal Ss is shown, and e is the waveform of the master station received signal Rm.

In the master station transmitting/receiving circuit 100, the master station side transmission signal Sm shown in FIG. It is received as the slave station side reception signal Rs shown in FIG. b.

Even in the "reception mode", for one signal corresponding to one piece of slave station transmission data transmitted from the slave station side to the master station side, 1 of the time width τ is transmitted as shown in Figure 3a. allocate 1 time slot and
The master station transmits the signal during time slot τ.
Sm is sent from the master station to the slave station as a synchronization signal for a time width tc. On the slave station side, received signal detection circuit 1
0 outputs a received signal Rs that is slightly delayed (td) with respect to the transmitted signal Sm, but the time width is longer than that of the transmitted signal.
It is the same tc as Sm. When the slave station transmits data, the slave station performs switching as an impedance variable means only during a part of the transmission period of the master station transmit signal Sm (that is, the period when the signal Sm is at a high level). Operate circuit 9.

The received signal Rs is input to the timing setting circuit 11, timing is controlled, and inputted to the data circuit 13. When the transmitted data Dss is "1", the data circuit 13 is delayed by te from the reception of the received signal Rs and has a pulse width tf. The signal Ss is outputted to the switching circuit 9, and when the data Dss is "0", the signal Ss is not outputted. Note that the time te is set so that (td+te) is approximately 1/2 of the pulse width tc of the transmission signal Sm shown in FIG. 3a. Further, the pulse width tf is set so that the falling edge is approximately equal to or slightly slower than the falling edge of the transmission signal Sm. In response to this, the received signal on the master station side
Rm becomes a signal with a small pulse width when the data Dss is "1", and becomes a signal with a large pulse width when the data Dss is "0".

Next, how the master station side received signal Rm shown in FIG. 3e is formed will be explained with reference to FIGS. 1 and 4.

First, in FIG. 1, attention is paid to the potential at a point a at one end of the master station winding P of the pulse transformer 5 provided in the master station. Even in the reception mode, the switching circuit 6
It is opened and closed by the master station side transmission signal Sm shown in Figures a and 4a. In other words, the master station side transmission signal
When Sm is at a high level, the switching circuit 6 is closed (on), and when Sm is at a low level, it is open (on). When the master station side transmission signal Sm is at a high level and the switching circuit 6 is closed, a current flows through the resistor 4, the pulse transformer 5, and the switching circuit 6 from the DC power supply Vcc.

According to the present invention, means is provided for receiving the transmission signal Ss from the slave station and obtaining the master station side reception signal Rm by comparing the above-mentioned current with a reference value. In this embodiment, the means includes a resistor 4 and a comparator 3 connected in series to the DC power supply,
The current value is converted into a voltage drop across the resistor 4, and the comparator 3 compares this with a reference voltage Vref.

The switch circuit 9 is configured to be open (off) when the slave station side transmission signal Ss is at a high level, and closed (on) when it is at a low level, so that the slave station side transmission signal Ss is at a high level, that is, If a pulse exists and the slave station switching circuit 9 is open (off), the impedance Z of the secondary side S of the pulse transformer 5 is Z ₀ (approximately 100 ohms), so the master station switching circuit 6 is When open (signal Sm is at high level), the following current flows through the primary winding P of the pulse transformer 5.

Ie+Vcc/Z ₀ +R ₁ (1) Here, Ie is the exciting current, R ₁ is the resistance value of the resistor 4, and the winding ratio of the pulse transformer 5 is 1:1.

On the other hand, when the slave station side transmission signal Ss is at a low level, that is, there is no pulse, and the slave station side switching circuit 9 is closed (on), the impedance Z of the secondary side S of the pulse transformer 5 becomes Z ₁ (approximately 0 ohm), and when the master station side transmission signal Sm is high level and its switching circuit 6 is closed (on), the following current flows in the master station side (primary) winding P of the pulse transformer 5. flows.

Ie+Vcc/Z ₁ +R ₁ (2) That is, the current flowing through the primary winding P of the pulse transformer 5, that is, the current flowing through the resistor 4, changes depending on the slave station transmission signal Ss. In this case, the above current 2
is larger than the above current 1, so the potential Va at point a
The voltage drop due to current 2 is larger than the voltage drop due to current 1.

Furthermore, if the transmission line 7 is disconnected, the impedance Z of the secondary winding S of the pulse transformer 5 becomes extremely high as Z ₂ (approximately infinity), and when the switching circuit 6 on the master station side is closed, the pulse transformer Primary winding P of device 5
The following current flows through.

Ie + Vcc / Z ₂ + R ₁ ≒ Ie ... (3) In other words, if only a small excitation current flows,
The voltage drop at point a is small.

Figure 4 is a waveform diagram of each part to explain the operation in the transmission mode, and a is the master station side transmission signal.
The waveform diagram of Sm is shown, b and c are waveform diagrams of the slave station transmission signal Ss when transmitting data Dss "1" and "0" from the slave station side, and the master station winding of the pulse transformer 5. A waveform diagram of the voltage Va at point a on the P side and a waveform diagram of the received signal Rm on the master station side are shown. A waveform diagram of the voltage Va at point a, and e a waveform diagram of the master station side received signal Rm.

The master station side transmission signal Sm shown in Fig. 4a is as shown in Fig. 3a.
It has the same waveform as the master station side transmission signal Sm shown in . First, the operation when the transmission data Dss is "1" will be explained. In FIG. 4b, when the signal Sm is at a low level, the switching circuit 6 is open (off), so the voltage Va is equal to Vcc. Next, when the signal Sm becomes high level and the switching circuit 6 is closed (on), the transmitted data is
When Dss is "1", the slave station transmission signal Ss is at low level at first, and becomes high level after a predetermined time (td+te in FIG. 3d). For this reason, the signal
When Ss is at a low level, the current shown by equation (2) above flows through the resistor 4 in Figure 1, so the voltage Va
decreases to voltage V ₁ as shown in FIG. 4b.
On the other hand, when the signal Ss is at a high level, the current represented by the above-mentioned equation (1) flows through the resistor 4, so the voltage Va becomes the voltage _V2 as shown in FIG. 4b.

In FIG. 1, the primary winding P of the pulse transformer 5
The voltage Va at the connection point a between the voltage V 1 and the resistor 4 is led to a comparator 3 and compared with a reference voltage Vref set to a value between the voltages V ₁ and V ₂ . The comparator 3 outputs a high level when the voltage Va at point a is lower than the reference voltage Vref, and a low level when the voltage Va is higher than the reference voltage Vref. This output is none other than the master station reception signal Rm shown in FIG. 4b.

Next, the operation when the transmission data Dss is "0" will be explained with reference to FIG. 4c. According to the present invention, when the transmission data Dss is "0", the slave station transmission signal Ss remains at a low level. Therefore, when the master station side transmission signal Sm is at a high level, the current shown by equation (2) above flows through the resistor 4, so the voltage Va is as shown in Figure 4c when the signal Sm is at a high level. Only the voltage drops to V ₁ . Since this voltage Va is compared with the reference voltage Vref in the comparator 3, the master station received signal Rm becomes equal to the signal Sm as shown in FIG. 4c.

Furthermore, if the transmission line 7 is disconnected, the current shown in equation (3) above flows through the resistor 4 when the master station side transmission signal Sm is at a high level, so the voltage Va is as shown in Figure 4d. As such, the voltage only drops to _V3 . Therefore, the voltage at comparator 3
The master station reception signal Rm obtained by comparing Va with the reference voltage Vref remains at a low level.

In this way, when the transmission data Dss is "1" or "0" and when the transmission line is disconnected, the received signal Rm on the master station side differs as shown in Fig. 4 b, c, and d. The signal Rm is branched into two, a received data detection circuit 22 and a transmission line state detection circuit 2.
Enter 3.

The data sampling clock generation circuit 21 generates first and second data sampling clocks CL ₁ and CL ₂ with the timing shown in FIG. , and sends the sampling results to the data circuit 1.

If the master station received signal Rm received from the slave station corresponds to data " ₁ " as shown in FIG. A high level "1" is sampled, and then a low level "0" is sampled in the received data detection circuit ₂₂ by the second clock CL2. As a result, the data circuit 1 identifies the received signal as corresponding to data "1" because "1" and "0" are sampled.

The master station side reception signal Rm received from the slave station side is the fourth
As shown in _{FIG .} Therefore, the received data detection circuit 22 has a high level “1”.
is sampled. As a result, data circuit 1
Since "1" and "1" are sampled, the received signal is identified as corresponding to data "0".

On the other hand, when the transmission line 7 is disconnected, the master station received signal Rm received from the slave station is at low level "0" as shown in FIG. A low level "0" is sampled in the transmission line state detection circuit 23 by the _second clock CL1, and then a low level "0" is sampled in the received data detection circuit ₂₂ by the second clock CL2. The data sampled by the transmission line state detection circuit 23 is "1" if it corresponds to the transmission data Dss "1" or "0", whereas it is "1" if the transmission line 7 is disconnected. Therefore, in the data circuit 1, if the data sampled by the transmission state detection circuit 23 is "0", it can be determined that the transmission line is disconnected. That is, according to the present invention, it is determined whether the transmission line is normal based on the data sampled by the transmission state detection circuit ₂₃ using the first clock CL1, and if it is normal, the second clock is
Based on the data sampled by the reception data detection circuit 22 by CL ₂ , it is determined whether the transmission data Dss is "0" or "1".

In other words, in the reception mode, the data circuit 1
is the time width of the master station side transmission signal Sm as a synchronization signal.
During the period in which only tc is sent to the slave station, the impedance variable means is operated according to the presence of data transmitted by the slave station in the first period (the period in which the signal Ss is at a high level in Figure 4b). The second sampling clock CL ₂ samples the slave station side transmission data, and the master station side transmission signal Sm is used as a synchronization signal with a time width.
During the period in which only tc is sent to the slave station side, the second period other than the first period (signal in Figure 4b)
The above-mentioned sampled slave station side transmission data is detected by the transmission line status signal (output of the transmission line status detection circuit 23) detected by the first sampling clock _CL1 during the period when Rm is at a high level. The effectiveness of the test is determined.

This transmission line status signal can easily be stored or displayed as so-called RAS (Reliability, Availability, Serviceability) information.

Although one embodiment of the present invention has been described above,
The present invention is not limited to the above-described embodiments, and various modifications can be made within the technical scope thereof.

For example, a configuration is possible in which the pulse transformer on either the master station side or the slave station side is removed and its connection end to the primary winding P is directly connected to the transmission line 7.

〔Effect of the invention〕

According to the present invention, since the transmission circuits on both the master station and slave stations are configured with extremely simple circuits, it can be used particularly in signal input/output devices for process control having a large number of input/output signal lines to reduce costs and improve reliability. In addition, the circuit system allows extremely efficient bidirectional transmission, and high transmission quality can be obtained even over relatively long distances.The impedance of the transmission circuit can be lowered, so it has excellent noise resistance. Moreover, due to the insulation of the pulse transformer, there is a difference in ground potential between the two
In addition to having all the advantages of the conventional bidirectional transmission method, such as being applicable to signal transmission between points, it also includes means for detecting the state of the transmission line.
It is possible to detect disconnections or disconnections in transmission lines, improve reliability, and further enhance RAS functions, and these effects can be achieved economically by adding only a small number of extremely simple circuits. .

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
The figure shows a time chart of each signal in the "transmission mode" of the embodiment shown in Fig. 1, and Fig. 3 a, b, c,
d and e are time charts of each signal in the "receiving mode" of the embodiment in FIG. 1, and FIG. 4 a, b,
c and d are waveform diagrams of each signal for explaining the operation in the "receiving mode" of the embodiment of FIG. 1. 100... Master station side transmitting/receiving circuit, 200... Slave station side transmitting/receiving circuit, 1, 2, 4... Data circuit, 3...
... Comparator, 4 ... Resistor, 5, 8 ... Pulse transformer, 6, 9 ... Switching circuit, 7 ... Transmission line, 10, 22 ... Received data detection circuit, 1
1...Timing/setting circuit, 21...Data/
Sampling clock generation circuit, 23... Transmission line status detection circuit, Sm... Master station side transmission signal,
Rm...Received signal on the master station side, Ss...Sent signal on the slave station side, Rs...Received signal on the slave station side.

Claims (1)

[Claims] 1 Signals are transmitted bidirectionally through a single transmission line that is connected via a pulse transformer included in both or one of the transmission/reception circuits on the master station side and slave station side. Switching means connected in series to the master station winding of the transformer, and transmitting means that opens and closes the switching means in accordance with the transmission signal or synchronization signal from the master station when the signal is sent to the slave station. and receiving means for receiving a transmission signal from the slave station by detecting the current flowing in the master station winding of the pulse transformer and comparing it with a reference value, the slave station having the transformer. impedance variable means connected in parallel between the child station side windings of the device;
a receiving means for receiving a transmission signal and a synchronization signal from the master station generated in the slave station winding of the pulse transformer; and a receiving means for receiving the transmission signal from the slave station based on the synchronization signal from the master station. transmitting means for controlling and changing the impedance of the impedance variable means during a first period included in the sending period of the synchronizing signal in order to transmit one of the transmission signals, and the transmission line is in a normal state. The reference value is set to the intermediate value of two received signals detected by the receiving means of the master station when the impedance of the impedance variable means is changed and when the impedance of the impedance variable means is not changed during the transmission period of the synchronization signal. The receiving means on the station side samples the received signal in the first period and a second period other than the first period in the transmission period of the synchronization signal, and compares the received signal with the reference value, and in the second period. A bidirectional transmission system characterized in that the validity of the comparison result of the received signals detected in the first period is determined based on the comparison result of the detected received signals.