JPS6035858B2 - Bidirectional transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for bidirectionally transmitting signals using a single transmission path.

Communication methods for data transmission can be classified into three types depending on the direction of information flow: unidirectional communication, half-duplex communication, and full-duplex communication.
It can be divided into Among these, full-duplex communication using a single transmission path is efficient and economical because information can be transmitted in both directions at the same time. In general, wired digital transmission requires not only technical conditions such as high quality transmission, but also extremely important economic conditions such as resource saving, low cost, and miniaturization of equipment. Normally, if you want to transmit signals bidirectionally between two isolated points, you can simply install a transmission line for each direction, but this would save resources and
In order to achieve low costs, it is necessary to economize on transmission lines.

Therefore, when multiple transmission lines are installed in the same direction between two points, they are combined into a single line and multiplexed transmission is performed.Furthermore, if you want to transmit signals in either direction, each direction Other transmission lines may also be combined into a single line and used as a bidirectional transmission line. In this case, if multiple lines in the same direction are combined into a single line, it is only necessary to consider parallel and serial conversion of the signals to be transmitted and improvement of the transmission speed, and there is no particular technical difficulty. However, when converting a single line into a bidirectional transmission line, prevention of signal collisions on the line must be taken into consideration, and there are many problems. Conventionally used methods for bidirectional transmission include the frequency division method shown in FIG. 1 and the time division method shown in FIG. 2.

In the bidirectional transmission circuit using the frequency division method, as shown in FIG. As shown in Figure 1 b, signal A→A' and signal B→
Collision is avoided by using different frequency bands FB, FB2.

However, in the frequency division method, the transmitting end and the receiving end are installed at the same location, so unless the signal level difference and frequency allocation are made appropriate, transmission quality will deteriorate.

Therefore, it is necessary to carefully design the filters 1 to 4 that pass through Obijo. Furthermore, since the signal must fall within a predetermined frequency band and baseband format signals cannot be transmitted, it is necessary to use an appropriate modulation method.
Therefore, the circuit configuration becomes complicated. Next, in a bidirectional transmission circuit based on a time division system, as shown in FIG. As shown in FIG. 2b, time t is divided into a signal A→A' and a signal B→B.
Collision is prevented by assigning time widths TW, , TW2 with different times to '.

However, the time-division method is inefficient because it can only transmit signals in one direction at the same time, and the transmitting side in each case has the initiative in both transmission directions, so it is difficult to synchronize. It is troublesome to take and does not allow high-speed transmission. As described above, in both the frequency division and time division systems, the circuit becomes complicated, so the cost ratio to performance increases, and the advantage of reducing the number of transmission lines is often lost. In addition, the special public
In the two-way communication method proposed in No.-21963,
As shown in Figure 3, the master station converts the NRZ signal into an RZ double current signal and sends it to line L, and the slave station receives this and reproduces the NRZ signal, and also converts the clock from the received RZ double current signal. Extract the signal, transfer it, and transmit the signal from the slave station.
A two-wire time-division bidirectional transmission system has been proposed in which the RZ signal is synchronized with the RZ signal, converted into an RZ signal, and sent to the master station.

That is, in FIG. 3, when the signal generator 20 of the master station generates an NRZ digital signal with a fixed amount of bits, the transmitting/receiving circuit 21G modulates this into an RZ pulse using the clock signal from the clock circuit 22. Transmission line L also sends out.

On the other hand, the PZ pulse sent from the slave station is sent to the transmitter/receiver circuit 2.
1. The signal is input to the identification circuit 24 via the transmission suppression circuit 23. The transmitting/receiving circuit 25 of the slave station inputs the RZ pulse sent from the master station to the identification circuit 29 via the transmission suppressing circuit 27, and at the same time shapes the RZ pulse using the pulse shaping circuit 30.

is applied to the output circuit 28. The clock circuit 28 generates a clock signal based on the output 0 of the pulse shaping circuit 30, and supplies this to the signal generator 26 to control the NRZ digital signal sent from the signal generator 26.

However, in this method, since the signal transmission from the slave station is regulated by the clock signal generated by the RZ signal sent from the master station, bidirectional signals do not collide on the transmission line.

However, since communication between the master station and slave stations is performed alternately on a bit-by-bit basis, it is not possible to transmit signals in both directions at the same time.

o The purpose of the present invention is to eliminate these drawbacks of the conventional method by using a time-division method, which enables simultaneous bidirectional transmission, has high transmission quality, and is low-cost and has a simple circuit configuration. The objective is to provide a bidirectional transmission system using a transmission line.

The present invention will be described below with reference to the drawings. FIG. 4 is a schematic block diagram, FIG. 5 is a detailed block diagram of FIG. 4, and FIG. 6 is a time chart of transmitted and received signals in FIG.

In the explanation of this embodiment, the parent station is described as the master side and the slave stations as the slave side, but there is no substantial difference.
Further, the master side transmitting/receiving circuit 31 connected to the data circuits 34, 35 and the slave side transmitting/receiving circuit 32 connected to the data circuits 36, 37 are connected by a single transmission line 33, The signal transmission from the slave side to the master side (direction A) is called the "transmission mode", and the signal transmission from the slave side to the master side (direction B) is called the "reception mode".

In order to make the "transmission mode" and "reception mode" distinguishable between the master side and the slave side, in the present invention, the information transmitted from the master side to the slave side and the information transmitted from the slave side to the master side are The data format of the information to be transmitted is determined to be 27 bits, for example, and a counter is provided on each of the master side and slave side, and the count value of this counter indicates that the 27-bit data transmission has been completed. One example is a method of detecting and switching between "transmission mode" and "reception mode."

2 First, in the "transmission mode", the signal from the data circuit 35 (this is
A master side transmission signal C shown by is sent to the transmission line 33 via the switching circuit 46, the circuit network 40, and the pulse transformer 38, and reaches the slave side transmission/reception circuit 32. In the slave side transmitting/receiving circuit 32, the slave side received signal D shown in FIG.
The signal is applied to data circuit 36. Next, in the "reception mode", the signal from the data circuit 35 (master side transmission signal C) is used as a synchronization signal in the reception mode, and is sent to the slave side transmission/reception circuit 32.

The slave side reception signal D mentioned above is a synchronization signal for transmission from the slave side to the master side, that is, the slave side control output signal E and the slave side transmission signal F (see Fig. 6 d) are generated by this synchronization signal. becomes the input of the horizontal logic circuit 49, and its output (slave side switch control signal G is given to the switching circuit 47.
The output signal of 7 is transmitted to the master side transmitting/receiving circuit 31 via the transmission line 33 through the circuit network 41 and the pulse transformer 39 . On the other hand, in the master side transmitting/receiving circuit 31, the pulse transformer 3
8. The received signal on the evening side after passing through the circuit network 40, the received signal amplification circuit 42 and the waveform shaping circuit 44 (see FIG. 6b)
is applied to the data circuit 34.

In addition, in FIGS. 6a to 6d, TM, . . . TM2 are in the transmission mode, and RM, . . . RM2 are in the reception mode.

Next, Fig. 5, Fig. 7 a to d, Fig. 8 a to h, Fig. 9 a,
The operation of the present invention will be explained in detail using FIG. Figures 7 a to d and Figures 8 a to h are time charts showing parts of Figures 6 a to d in detail;
The figure shows the transmission mode, and FIG. 8 shows the reception mode. Note that the symbols representing each signal correspond to those in FIG. Also, the 9th
Figures a and b' are connection diagrams showing some details for explaining the principles of the master side transmitting/receiving circuit and the slave side transmitting/receiving circuit in Figure 5, and Figure 10 shows the rebound voltage generated in the pulse transformers 38 and 52. FIG.

Thus, in the transmission mode, the transmission data TD of FIG.
The master side transmission signal C shown in FIG. 7b, which has undergone pulse modulation by
In addition to this, the switching circuits 46 and 56 are repeatedly turned on and off.

At this time, the master side transmission signal C has data "0↓" according to pulse widths ta and tb for one time slot.
1" is distinguished. Note that the switching circuits 46, 5
6 is "switched on" when the signal C is "0". In addition, in the transmission mode, the switching circuits 47 and 61 of the slave side transmission/reception circuit 32 are "switched off".
Therefore, the circuit network 41 should not be affected. The switching circuits 47 and 61 are "switched off" when the slave side switch control signal G becomes "0".
becomes. When the switching circuits 46 and 56 repeat "switch off" and "switch on" in response to the signal C, the pulse transformers 38 and 52 are driven by the current from the power source 51. At this time, since the switching circuits 47 and 61 on the slave side are switched off, the pulse transformer 3
A matching circuit 57 and received signal amplification circuits 43 and 59 are connected as load resistances to matching circuits 9 and 58, and the matching circuit 5
7. The load current flows through the pulse transformers 39, 58 and the multiplier circuits 43, 59 (the load current flows to the ground via the large internal resistance in the multiplier circuits 43, 59).
, this load resistance is a very large impedance, so this load current is small. switching circuit 46
, 56 are "switched on" or "switched off" in response to signal C, the master side pulse transformers 38, 52
FIG. 10 shows the waveforms of the excitation current and load current flowing through the motor. In FIG. 10, a is the waveform of signal C;
becomes "0" and the switching circuits 46 and 56 are turned on, the excitation current iL shown in b and the load current iR shown in c flow, and the total current iL + iR as shown in d flows.
flows. The load resistance value converted to the primary side of the pulse transformers 38 and 52 is R, the inductance is L, the internal resistance of the power supply 51 is r, the voltage is V, and the switching circuits 46 and 56 are
When the time during which the switch is on is t, the excitation current iL and the load current iR are expressed by the following equations.
．． V R ……{1) IL=anti-old/tt. V...・Misaki IR=Misaki IR This load current makes it possible to obtain a delayed reception signal on the slave side, as shown in FIG. 7c.

The data circuit 36 on the slave side can faithfully reproduce the transmission data TD shown in FIG. 7a by demodulating the pulse width modulated reception signal D. In this transmission mode, the impedance of the pulse transformers 38 and 52 on the mass and evening side is very high, so the impedance accumulates at the moment the switching circuits 46 and 56 change from "switch on" to "switch off". The energy that was being used bounces and is transferred to the primary side as a voltage, and the charge that flows through the diode CR is charged to the capacitor CX, keeping the cathode side of the diode CR at a high potential until the next drive state. .

The charge stored in the capacitor cx is then discharged when the switching circuits 46, 56 are "switched on". The switching circuits 47 and 61 on the slave side are
When the switch is off, the load resistance of the pulse transformers 38, 52 on the secondary side has a very large impedance as described above, so that only a small amount of the load current is transmitted to the secondary side and the pulse transformer 38, 52 is switched off. A large amount of energy is stored in 52.

This stored energy is transferred to the switching circuits 46, 5
6 is "switched off", a rebound voltage is induced on the primary side. This rebound voltage is shown in Figure 10e.
The waveform will be as shown. However, on the master side,
As mentioned above, it is counting the number of bits of the transmission signal C and recognizes that it is currently in "transmission mode", so
By ignoring the received signal date on the master side at this time, or by locking the received signal amplification circuits 42, 54 or the waveform shaping circuits 44, 55, the signal due to the bounce voltage at this time can be adjusted to the received signal date on the master side. Try not to think of it as such. Next, in the "reception mode", the master side transmission signal C shown in FIG. After passing through the circuit 41, received signal amplification circuits 43 and 59, and waveform shaping circuits 45 and 60, a slave side received signal D shown in FIG. 8e is obtained.

Note that the slave side received signal D is transmitted to the switching circuit 47.
, 61 are "switched off", that is, when the switch control signal G is "1", the master side transmission signal C
is shown as being delayed, but during the period when the switching circuits 47, 61 are "switched on", the inputs of the received signal amplification circuits 43, 59 are at ground potential, so they are "0". The slave-side received signal D shown in FIG. 8e is converted into a slave-side control signal E in the control circuit 48 with a width (t2-t,) delayed by the amount that tends to fall as shown in FIG. The slave side transmission signal F(
FIG. 8g) and the signal E are logically ANDed to form the switch control signal G (FIG. 8h), which is output to the pulse transformer 39,
58 to the transmission lines 33, 53. At this time, since the slave side also identifies the "transmission mode" and the "reception mode" by counting the number of bits of the data, the reception signal D shown in FIG. 8e is ignored. Note that the switch control circuit G is the switching circuit 4.
7, 61, the data circuit 36 continuously receives the synchronization signal (slave side reception signal D), and a rebound voltage is generated on the master side in response to the slave side transmission signal F. When the switch control signal G is "1↓", that is, the switching circuits 47 and 61 are "switched off" at the time of falling of the received signal D, and the slave side transmission signal F is "0", the eighth
At the rising edge of the transmission signal C in FIG.
t and t2 of the slave side control output signal E are set in advance to appropriate values in relation to one time slot T and pulse width tc so that the slave side control output signal E is turned on. On the master side, in the reception mode, the transmission signal C is transmitted to the slave side as a transmission synchronization signal, and this synchronization signal is detected and observed as a reception signal on the master side. It changes depending on F as follows.

First, at each falling point of the signal C, that is, when the switching circuits 46 and 56 are "switched on," the slave side received signal D is still "1", and therefore the switching control signal G is also "1". ”, the switching circuits 47 and 61 are “switched off”. Therefore, the secondary side impedance of the pulse transformers 38 and 52 on the master side is very high, so that only a small amount of the load current on the primary side is transmitted to the secondary side, and the pulse transformer 38, 52 on the master side has a very high impedance.
A large amount of energy is accumulated in 8 and 52. Further, due to this slightly transmitted load current, a slave-side received signal D is obtained on the slave side as shown in FIG. 8e. In this state, the slave side transmission signal F is “
1", the switch control signal G remains at "1", so at the time the signal C rises, that is, the switching circuits 46, 56 are "switched off", the pulse transformers 38, 52 are switched off. On the next side, a large rebound voltage is generated as shown by the symbol A in FIG. 8b, and this rebound voltage charges the capacitor Cx via the diode Cr as shown in FIG. 8c.

This charging voltage is only slightly discharged and the voltage decreases depending on the charging/discharging characteristics of the capacitor Cx until the signal C falls again and the switching circuits 46, 56 are "switched on" and discharge occurs. It is kept at a high potential.
On the other hand, if the slave side transmission signal F is "0", the signal E becomes "0", and the switch control signal G
becomes "0", and the switching circuits 46 and 56 become "switched on". As a result, the secondary impedance of the pulse transformers 38 and 52 on the master side is reduced to 4.
Since most of the subsequent load current is transferred to the secondary side, less energy is stored in the pulse transformers 38, 52. Therefore, at the time when the signal C rises, that is, when the switching circuits 46, 56 are "switched off", the primary side of the pulse transformers 38, 52 is
Only a small rebound voltage is generated, as indicated by the symbol in FIG. Therefore, the eighth
The charging voltage of the capacitor cx as shown in FIG.
By binarizing at level L as shown in FIG. 8, a signal as shown in FIG. 8d can be obtained as a received signal.

The data circuit 34 detects the reception signal date at a predetermined time within the period up to the time slot within one time slot 7 of the master side reception signal date, and determines that the reception signal date is "1". If the received signal date is "0", the data sent from the slave side is considered to be "0".
Data is received from the slave side by assuming that In this way, the pulse transformers 38, 5 on the master side
2, the rebound voltage generated at pulse transformer 38, 52
The secondary side, that is, the state of the slave side pulse transformers 39 and 58 coupled by the transmission line, will affect the relationship, and this relationship is as shown in the following table.

Using this relationship, the present invention converts the state of the switching circuit on the slave side into the magnitude of the rebound voltage of the pulse transformer on the master side, and makes a logical judgment based on the voltage across the capacitor C.

In this way, in the present invention, the synchronization signal can be transmitted from the master side to the slave side during the period of one time slot 7 in the reception mode, and the signal transmission from the slave side to the master side can be completed. The evening side can take the lead in synchronization both in signal transmission and reception, and it also allows for a simpler circuit configuration than a simple slave synchronization method.

Also, since bidirectional signal transmission is possible within the period of one time slot in the receiving mode, double-current signals (k) are generated during transmission, compared to the time-division bidirectional transmission method shown in FIG.

This eliminates the need for phase shifting means for the clock signal, and there is no need to use double current in the signal format. Note that the temporal combination of the transmission mode and the reception mode can be made in any manner, for example, depending on the number of bits of the data format, so that it can be applied to a wide range of transmission control systems, from simple to complex.
As explained above, according to the present invention, the simple principle of controlling the rebound voltage generated when switching the inductive load using a pulse transformer is used, so bidirectional transmission is possible with an extremely simple circuit. Moreover, a synchronization signal can be transmitted from one side and a transmission signal can be transmitted from the other side during one time slot.

Since this synchronization signal is constantly transmitted from the receiving side to the transmitting side, high-speed response is possible, and only one side needs to have the synchronization signal for sending and receiving, and the other side is dependent on that synchronization. do it. Note that if the present invention is applied to a process control signal input/output device having a large number of input/output signal lines, the number of signal lines can be saved and peripheral circuits can be realized at low cost. In addition, since the isolation method uses a transformer, it is suitable for signal transmission in places where the potential reference points between two points are different, and there is no need to balance both pulse transformers with a grounded center tap. do not have. Furthermore, since the power supply voltage is determined separately at both points, it is possible to use peripheral logic elements with different power supply voltages, such as TTL and C-MOS, and to optimize the design of the power supply device.

[Brief explanation of drawings]

Fig. 1 a, b and Fig. 2 a, b are explanatory block diagrams and waveform diagrams showing conventional bidirectional transmission systems, respectively, and Fig. 3 is a previously known two-wire time-division bidirectional transmission system. Figure 4 is a schematic block diagram of a bidirectional transmission system showing an embodiment of the present invention; Figure 5 is a detailed block diagram of Figure 4; Figure 6 is a block diagram of the system;
Figures a to d show the time and frequency of the transmitted and received signals in Figures 6 a to f.
7 and 8 are time charts showing details of parts of FIG. 6 a to d, respectively, and FIGS. 9 a and b are partial details for explaining the principles of both transmitting and receiving circuits in FIG. 5. 10 is an explanatory diagram of the rebound voltage of the pulse transformer. 31: Master side transmitting/receiving circuit, 32: Slave side transmitting/receiving circuit, 33, 53: Transmission line, 34 to 357: Data circuit, 38, 39, 52, 58: Pulse transformer, 40, 41
: Circuit network, 42, 43, 54, 59: Received signal amplification circuit, 44, 45, 55, 60: Waveform shaping circuit, 46, 47
, 55, 61: switching circuit, 48: control circuit, 4
9: 0 AND circuit, 61: Power supply, 57: Matching circuit, C:
Master side transmission signal, D: Slave side reception signal, E: Slave side control output signal, F: Slave side transmission signal, G: Slave side switch control signal, H: Master side reception signal. Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 9

Claims (1)

[Claims] 1. Bidirectional transmission is achieved through a single transmission line that is connected via a pulse transformer included in a master (parent station) side transmission/reception circuit and a slave (slave station) side transmission/reception circuit, respectively. , the master side has means for sending a transmission signal or a synchronizing signal from the master side switching means to the master side pulse transformer to the slave side, and the master side pulse transformer is brought into a non-driving state by a signal from the slave side. The slave side is equipped with a means for monitoring the voltage induced on the primary side of the pulse transformer to obtain a received signal, and a means for controlling the timing of the slave transmission signal based on the synchronization signal from the master side. means for controlling slave-side switching means using the control output to deactivate the master-side pulse transformer;
means for creating a slave-side switch control signal using a part of the signal based on the transmission signal from the master side, controlling the slave-side switch means, and faithfully demodulating the transmission signal from the master side as a reception signal. A two-way transmission system characterized by: 2 Using the control output from the slave side, when the master pulse transformer is deactivated, the stored energy is converted into a rebound voltage caused by the switching of the inductive load and is applied to the primary of the master pulse transformer. The device is characterized in that it includes connection means for causing the diode to flow through the diode and charge a capacitor connected to the cathode side of the diode to maintain the cathode side of the diode at a high potential until the next driving state. Claim 1
Bidirectional transmission method described in section. 3. In order to control the timing of the slave transmission signal based on the synchronization signal from the master side, the synchronization signal is given to the AND circuit as the slave side control signal D and the slave side transmission signal F in the slave side transmission/reception circuit, and its control output is 3. The bidirectional transmission system according to claim 1 or 2, wherein the slave side switching circuit is opened using G and the master side pulse transformer is not driven.