JPS5940737A - Bidirectional transmission circuit - Google Patents

Abstract

PURPOSE:To improve the utilizing efficiency of a transmission circuit, by transmitting outgoing and incoming signals with different potential levels to attain bidirectional data transmission via a pair of transmission lines. CONSTITUTION:When the outgoing signal to each terminal is transmitted to a transmission transistor(TR) 6 at the center side 1, the TR6 is driven to convert a signal into the outgoing signal having a high power supply voltage VCCT level, and the signal is transmitted to a signal line 3. Since the voltage VCCT exceeds the Zener voltage of a Zener diode 9 at a terminal side 5, a current corresponding to the outgoing signal flows to the Zener diode 9, a resistor 10, and an LED11, and the outgoing signal is converted into a receiving signal by a photocoupler 8. When an incoming signal is given to a transmission TR14, the TR14 applies the incoming signal of the VCCR power supply voltage level to the signal line 3. Then, the incoming signal is converted into the receiving signal by a photocoupler 15. Since the potential of the signal line 3 in this case goes to the VCCR or below lower than the Zener voltage of the Zener diode 9, no outgoing signal is received by the photocoupler 8.

Description

[Detailed Description of the Invention] A) Industrial Field of Application The present invention transmits T-C bonds from the center side to the terminal side and transmission signals from the terminal side to the center side via a pair of transmission lines. This invention relates to a bidirectional transmission circuit.

Summary) Transmission of the J signal of one potential level and transmission of the rising potential level of the other potential level are performed via the pair of transmissions 41jl, and the terminal tf
A bidirectional transmission circuit that uses a first receiving means provided at K and a second 9-fold class provided at the center side to detect signals of one potential level and another potential level, respectively.

8) Prior Art Conventionally, data transmission between the central processing unit on the center side and the terminal equipment is performed by providing two pairs of transmission lines between the center side and the terminal side, one transmission line being used exclusively for upstream signals, and the other transmission line being used exclusively for upstream signals. This was done by using the transmission line exclusively for upstream transmission.

2) Problems to be Solved by the Invention However, with such a transmission circuit, an inquiry signal can be sent from the center to the terminal 11, and from the terminal side to the center (b).
When used in a half-double direct transmission system in which response signals and response signals are transmitted alternately, one of the two pairs of transmission lines is not used, resulting in poor usage efficiency of the transmission lines.

e) Means for solving the problems The present invention has been made in view of the above points Vc,
The present invention provides a bidirectional transmission circuit that performs bidirectional data transmission between a center side and a terminal side via a pair of transmission lines by transmitting the downstream and upstream signals with different potential levels.

to) Example t! Figure J1 is a circuit diagram that does not include an embodiment of the transmission circuit of the present invention, in which (1) is a center multiplication control circuit provided at the center 1lIJ and transmits downlink signals and receives uplink signals; ) is this center communication system ill! ? J road (1)
Tsukuda line (3) and earth line (4) extended from
), +51ti, and this transmission line f2
A terminal communication control bWI is connected to the terminal terminal and transmits uplink signals and receives downlink signals, and a plurality of normal transmission lines (2) are provided as m lines. (6) is Center Dori Q
4 control circuit W11 (11) is a first transmitting transistor serving as a first transmitting means provided in the control circuit W11 (11). ) to the signal line (3), and the transmitting side '19 (DT) from the central processing unit (not shown) is applied to the base. (8)
1 shows a photocoupler constituting the first receiving means provided with the terminal communication control circuit +5) VC, which forms a series circuit with a Zener diode (9) and a resistor 11111 to connect the feed line (3) and the ground line (4). ) and a phototransistor a that receives the light from this L-ED[l. By turning on and off this phototransistor lIz, the power is supplied via the resistor Q31. The change in the collector potential of VOCTVCM is transmitted as reception voltage 1 (Dr) to the terminal (not shown).The Zener voltage of the Zener diode (9) is lower than the voltage 12V of the power supply VCCT. candy,
For example, it is set to 7v. The second transmitting transistor constituting the second transmitting means attached to the terminal communication control circuit (5) is blank, and the signal line (3)
, and the ground line (4), and is turned ON and OFF by the transmitter @ (Dt) from the terminal. A shows a photocoupler constituting the second receiving means provided in the center-side communication control circuit fl)K, which forms a series circuit with the backflow prevention diode fiG and the resistor αη to connect the power supply VCQB and the signal line (3). LEDQ&
and a phototransistor a1 that receives light from this LEl]1110.

This phototransistor a9 is turned on and off.
As a result, the collector potential connected to the power supply vCC via the resistor Cα is transmitted to the central processing unit as a reception borrow (DR). In this case, the power supply VCOR has a voltage slightly lower than the Zener voltage of the Zener diode (9).
For example, it is set to +6V.

In a bidirectional transmission circuit with such a configuration, central control)
A downlink signal CD? is sent from the device to the first transmitting transistor (6) as an inquiry signal for making an inquiry to each terminal. )
is sent, and this transistor 16) becomes 0N-O.
FFy1 converts the inquiry signal into a down signal at the high power supply voltage VcOT level as shown in period A in FIG. 2, and sends it to signal line (3) u4. In the terminal communication control circuit (5), the telegraph VOC given to the signal line (3)
If T exceeds the Zener voltage of the Zener diode (9), the current corresponding to #C will flow through the Zener diode (9).
9J, resistance strike, old LED), and the lower signal is converted to a reception signal 8 (Dr) at 81 and transmitted to the terminal.

On the other hand, the downlink loli transmission is finished and from the terminal.

When the response signal Q(I)t is transmitted to the second transmitting transistor (141), this second transistor is driven ON, O, and FF by the upstream ';j, and the VO
The rise of the CR power supply voltage level 9 is shown in period B in Figure 2 tf
fl<, 8fj is supplied to the signal line (3). Z to this
t), J#v Oc n color L E Dt+8.
WMIn, conversely, the #li current flows through the prevention diode mark A and the second transistor A,
The photocoupler a9 converts the reception signal into a DR signal and sends it to the central processing unit a. At this time, the signal line (37 (Q) is lower than the Zener voltage of the Zener diode (9J), so the photocoupler (8) constituting the first receiving means receives the upstream signal.
It will not be done.

g) Effect As explained above, the bidirectional transmission circuit of the present invention has the following features.

The lower signal and the upper signal are transmitted with different potential levels, and a first receiving means is provided on the terminal side to detect the potential level of the lower signal, and a second receiving means is provided on the center side to detect the potential level of the upstream signal. Since the receiving means of the V! This increases the efficiency of transmission line usage and reduces the cost for setting the transmission line fPI.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the bidirectional transmission circuit of the present invention, and Fig. 2 shows the potential state of the signal line. FIG. (1)...Center communication control circuit, (2)...Transmission line, (5)...Terminal communication (,4 control circuit, (6)...
@1 transmitting transistor, [81+151...photo coupler, (9)...zener diode, ■...
A first transmitting transistor. >).

Claims (1)

[Claims] 1) In a bidirectional transmission circuit that connects the center and the terminal side using a pair of transmission lines and performs bidirectional data transmission via this transmission line, a power source that outputs potentials at different levels; A first transmitting means is provided on the center side and sends a downstream signal to the transmission line as a signal at one potential level of the power supply; A second transmitting means is connected to the terminal side and transmits the upstream signal to the transmission line by borrowing the upstream signal from the other level of the power source, and a second transmitting means is installed at the center side and transmits the upstream signal from the transmission line. A second circuit that detects signals at other potential levels.
1. A bidirectional transmission circuit comprising: a receiving means, and transmitting an upstream signal of a negative potential level and an upstream signal of another potential level via a pair of transmission lines.