JPS6248423B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a bidirectional transmission circuit, and when a plurality of terminals are connected to a control station (electronic computer) and half-duplex data communication is performed on the same line, the communication circuit The aim is to improve economic efficiency and noise resistance.

Conventionally, in order to perform half-duplex (bi-directional transmission, transmission is performed only from one side) data communication between a control station and a terminal on the same line, the same circuit as the control station was connected to the terminal. I needed it on my side too. Therefore, as the number of terminals increases, it becomes extremely expensive and there are also problems with noise resistance.

It is an object of the present invention to provide a bidirectional transmission circuit that does not have these conventional drawbacks. In order to achieve this object, the present invention connects a control station transmission circuit to one end of the balanced line, and connects a plurality of terminal transmission circuits in parallel at any point in between, and the control station transmission circuit is composed of a transmission electrode, a transmitter for driving a balanced line, a resistor inserted into a line that crosses the input and output sides of the transmitter, and a receiver, and the terminal transmission circuit includes an optical coupling element, etc. It consists only of a receiver and a transmitter such as a semiconductor switching element.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 1, reference numerals 1 and 2 indicate balanced lines. A control station transmission circuit 3 is connected to one end of the balanced lines 1 and 2, line terminating resistors 4 and 5 are connected to the other end, and between them, Multiple terminal transmission circuits 6 ₁ at any location,
Connect 6 ₂ ,...6n.

The control station transmission circuit 3 includes DC power supplies 7 and 8 provided only on the control station side (not provided on the terminal side), a control station transmitter 9 inserted in the lines 1 and 2, This transmitter 9 and line protection resistor 1
Lines 12 and 13 that crossed between the input and output sides of 0 and 11
The receiver 16 includes resistors 14 and 15 inserted into the receiver 16.

As shown in FIG. 2a, the control station transmitter 9 includes an optical coupling element 17,
Insert 18 phototransistors 19 and 20,
Further, the anodes of the light emitting diodes 21 and 22 are connected to the power supply terminal Vcc, and the cathodes are connected to the collectors of the switching transistors 23 and 24, respectively.
The bases of these transistors 23 and 24 are connected to an on/off transmission data signal input terminal 25, and the emitters are grounded. In this Figure 2 a,
If the data signal "1" or "0" is expressed as "on" or "off" on the transmission line, the control station transmitter 9 is in the off state when the transmission data signal is "0", and the resistor 14 Therefore, a negative off signal voltage is applied to the first line 1 side and a positive off signal voltage is applied to the second line 2 side. Conversely, when the transmission data is "1", the control station transmitter 9 is in the on state, and the on signal voltage is applied to the line. In this case, as shown in Figure 2a, the line 1,
Instead of directly inserting the optical coupling elements 17 and 18 into the lines 1 and 2, switching elements such as transistors that are opened and closed by these optical coupling elements 17 and 18 are connected to the lines 1 and 2.
It is also possible to insert the transmission data signal into the line switching element and supply the transmission data signal to the line switching element via these optical coupling elements 17 and 18.

The receiver 16 of the control station transmission circuit 3 includes a resistor 2 between the first line 1 and the second line 2, as shown in FIG. 2b.
6. The light emitting diode 28 and the Zener diode 29 of the optical coupling element 27 are coupled, and the collector of the phototransistor 30 is connected to the received data signal output terminal 3.
1 and to the power supply terminal Vcc via a resistor 32, and its emitter is grounded. In FIG. 2b, the receiver 16 is connected in such a direction that current flows through the light emitting diode 28 of the optical coupling element 27 when the line is off, and does not flow when the line is on. Further, since the on-state detection of the receiver 16 is performed when the line voltage is near OV as will be described later, the detection level is raised by the Zener diode 29 to increase the noise margin.

Next, the transmitter 33 of the terminal transmission circuit 6n
As shown in Figure 3a, n is between the lines 1 and 2,
A phototransistor 35 of the optical coupling element 34 is inserted, and the anode of the light emitting diode 36 is connected to the power supply terminal Vcc via the resistor 37, the cathode is connected to the transistor 38, and the base of this transistor 38 is connected to the transmission data signal input terminal 39. has been done. With this configuration, the transistor 38 is turned on and off by the transmission data signal, and the optical coupling element 34 is opened and closed to turn on and off between the lines.
It's off.

The receiver 40n of the terminal transmission circuit 6n has a resistor 41 and a light emitting diode 43 of an optical coupling element 42 inserted between the lines 1 and 2, and the collector of the phototransistor 44 is connected to the power supply terminal Vcc, and the emitter is connected to the received data output terminal 45 and grounded via a resistor 46. With such a configuration, the receiver 40n can switch from the first line 1 to the second line by on/off data signals.
A received data signal is obtained depending on whether a current flows in the light emitting diode 43 in the direction of the line 2.

Next, the operation of the present invention will be explained.

First, a case in which data is transmitted from a control station to a terminal device will be explained. Incidentally, since the communication procedure is performed according to a command (boring selection) from the control station, both sides will not be in the transmitting state at the same time.

In the transmission stop state, the transmission data signal is set to 0, and the line is turned off. In other words, input terminal 25 is 0
Therefore, the transistors 23 and 24 are turned off, the optical coupling elements 17 and 18 are also turned off, and the first line 1 becomes negative and the second line 2 becomes positive. Therefore, the optical coupling elements 42 of the terminal receivers 40 ₁ .

Next, when the transmission data signal is set to 1, the transistors 23 and 24 are turned on, and the optical coupling elements 17 and 18 are turned on.
is also turned on, that is, the line is turned on, and a positive voltage is applied to the first line 1 and a negative voltage is applied to the second line 2. Then, the optical coupling element 42 of the terminal receiver 40n is turned on, and the received data signal becomes 1. The levels of the lines 1 and 2 of the terminal receivers 40 ₁ . . . 40n described above are shown in FIG. 4a.

Next, the case of data transmission from the terminal to the control station will be explained.

In the transmission stop state, the line is in the off state as described above, the first line 1 is at a negative potential, and the second line 2 is at a positive potential. Then, the Zener diode 29 of the control station receiver 16 is turned on, a current flows through the light emitting diode 28, the optical coupling element 27 is turned on, and the received data signal output becomes zero.

Next, the terminal transmission data signal "1" is sent to the transmitter 3.
When applied to the input terminal 39 of 3n, the transistor 38 is turned on, the optical coupling element 34 is turned on, and the lines 1 and 2 are short-circuited. Then, the potential difference between the lines 1 and 2 becomes approximately OV as shown in FIG. It turns off, and the received data signal output becomes 1.

In addition, the detection level L is detected by the Zener diode 29.
The purpose of setting is to prevent malfunctions due to noise signals closer to OV than the detection level L applied to the lines 1 and 2.

In the above embodiment, the data signal lines 1,
Although the optical coupling element is interposed as an element for insulation at the time of input to or output from 2, the present invention is not limited to this.

As mentioned above, the present invention is equipped with a power supply for transmission only on the control station side and is not required for each terminal, and the transmitter of the terminal is a simple transistor such as a transistor that only shorts or opens the line. It has characteristics such as being a switching element, employing a balanced line, high signal level, and high noise tolerance due to positive/negative inversion voltage. Further, by using an optical coupling element, it is possible to electrically insulate the data generation section and the transmission circuit, and to adjust the gain for frequency signals in an unnecessary range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the bidirectional transmission circuit according to the present invention, and FIGS. 2a and 2b are specific electrical circuit diagrams of the transmitter and receiver of the control station transmission circuit in FIG. Figure 3 a and b are the first
4A and 4B are characteristic diagrams of the terminal receiver level and the control station receiver level, respectively. 1, 2...Balanced line, 3...Control station transmission circuit,
4, 5... Termination resistor, 6 ₁ to 6n... Terminal transmission circuit, 7, 8... DC power supply, 9... Control station transmitter, 16... Control station receiver, 33 ₁ to 33n...
Terminal transmitter, 40 ₁ to 40n...Terminal receiver.

Claims (1)

[Claims] 1. In a transmission circuit in which a control station transmission circuit is connected to one end of a balanced line, a line terminating resistor is connected to the other end, and one or more terminal transmission circuits are connected in parallel between them, the control station transmission circuit is The station transmission circuit includes a power source for transmission, a transmitter for driving a balanced line, a resistor inserted in a line that crosses and couples the input and output sides of this transmitter, and a receiver provided between the balanced lines. The terminal transmission circuit consists of a receiver that opens and closes between lines depending on the presence or absence of a signal, and a transmitter consisting of a switching element, and the transmitter of the control station is an optical coupling device inserted into each of the balanced lines. The receiver of the control station is composed of NPN type and PNP type phototransistors as elements, and a light emitting diode as the optical coupling element whose light emission is controlled by turning on and off the transistors using on/off signals of data signals. consists of a light-emitting diode as an optical coupling element inserted between balanced lines, a Zener diode for setting the detection level, and a phototransistor connected to a data signal output terminal that is controlled to turn on or off depending on whether or not the light-emitting diode emits light. The receiver of the terminal device consists of a light emitting diode as an optical coupling element inserted between the balanced lines, and a phototransistor connected to a data signal output terminal which is controlled to turn on or off depending on whether or not the light emitting diode emits light. The transmitter of the terminal includes a light-emitting diode, which is an optically coupled device whose light emission is controlled by a transistor that opens and closes in response to an on/off data signal, and a light-emitting diode that is inserted between the balanced line and determines whether or not the light-emitting device emits light. It consists of a phototransistor, which is an optical coupling element that turns on and off, and a single
A bidirectional transmission circuit that enables half-duplex communication on a balanced line.