JPH0787408B2 - Signal transmission device - Google Patents

Description

The present invention relates to a signal transmission device of a type in which a main controller and a plurality of terminals are connected to a common signal transmission line to exchange signals.

"Prior Art" For example, as shown in "Japanese Patent Publication No. Sho 63-31785", there is a two-wire type display device which uses a two-wire type signal transmission line to display the employee's arrival and departure status.

An outline of the signal transmission line of this two-wire type display device is shown in FIG.

In the figure, 100 is a two-wire signal transmission line, 200 is a main controller, 300A to 30
0N indicates a terminal device.

The terminals 300A to 300N are, for example, a display equipped with a plurality of display windows or an operating device for switching the display state of the display.

A light emitting element is attached to each of the plurality of display windows of the display, and the light emitting element is controlled to be turned on and off in accordance with an instruction input from the operating device, and the employee's coming to and leaving from the office is displayed on the display window. The operation unit is provided with an input means such as a switch, and the display state of the display window of the display is controlled by the input operation of this input means.

The terminals 300A to 300N are display devices or operation devices as described above, and these have a function of transmitting and receiving signals to and from the main controller 200.

In other words, in the display unit, the signal reception function that captures the display data sent from the main controller 200 and the status that is currently being displayed are sent back to the main controller and sent to check whether the display is correct or not. And functions are added.

Further, in the operating device, a display is provided side by side with the input means, a transmission function for sending to the main controller 200 that the display switching input is given from the input means, and the fact that the display switching was actually performed are input means. A signal receiving function for taking in display data sent from the main controller for displaying on an attached display is provided.

Therefore, in any case, each of the terminals 300A to 300N is provided with the signal transmitting circuit 10 and the signal receiving circuit 20, and each of the terminals 300A to 300N.
The signals transmitted from each of the 300N are taken into the receiving circuit 20 of the main controller 200, and also the signal transmitting circuit 1 of the main controller 200.
The signal transmitted from 0 is taken into each signal receiving circuit 20 of each terminal 300A to 300N.

Also, as disclosed in Japanese Unexamined Patent Publication No. 59-40737, two kinds of power sources of different sizes are used for transmitting signals, two receiving sensitivity levels are set according to the purpose of the receiving circuit, and the same transmission line is used. There is a method to realize two-way communication, but since there is only one power supply (two power supplies are used, but one is actually one because it is twice the other), the degree of freedom is poor and the noise margin is small. Since it is a current control type, there are problems such as large power consumption.

"Problems to be solved by the invention" In the conventional device of this type, from each terminal device 300A to 300N to the main controller
The amplitude of the signal sent to the 200 and each terminal from the main controller 200.
A pulse signal with an amplitude of about 5V is used for the signals sent to 300A to 300N.

Therefore, each receiving circuit 20 of each of the terminals 300A to 300N has a function of receiving the pulse signal having the amplitude of 5V. Therefore, the signal transmitting circuit 10 provided in each of the terminals 300A to 300N is provided in addition to the receiving circuit 20 of the main controller 200 and all the terminals 300A to 3N.
The receiving circuit 20 provided at 00N must also be driven.

An amplifier with high input impedance is used for each receiving circuit 20, but even if the input impedance is high, if the number of receiving circuits 20 connected in parallel reaches about 100, the receiving circuits 20 connected in parallel will be It will be a considerable load.

As a result, there is a drawback that the controllable power capacity of the signal transmitter 10 provided in each of the terminals 300A to 300N must be large.

In addition, the cost of each of the terminals 300A to 300N is also high because of this.

An object of the present invention is to propose a signal transmission device capable of reducing the cost of each terminal.

"Means for Solving the Problem" In the present invention, a constant voltage diode is inserted in series to each of a pair of input sides of a signal receiving circuit of each terminal (a device configured with this constant voltage diode is called a level shifter), and main control is performed. The amplitude of the signal sent from the terminal to each terminal is set higher than the shift voltage of this level shifter, and the amplitude of the signal sent from each terminal to the main controller is selected lower than the shift voltage of the level shifter.

According to the configuration of the present invention, the signal transmitted from the signal transmission circuit of each terminal is not taken into the receiving circuit of each terminal. In other words, since the signal transmitted from the signal transmission circuit of each terminal cannot make the level shifter conductive, current does not flow into the receiving circuit of each terminal, and current is driven only in the receiving circuit of the main controller. .

Therefore, the power capacity of the signal transmission circuit of each terminal can be reduced, and the advantage that the signal transmission circuit of each terminal can be manufactured at low cost can be obtained.

[Embodiment] FIG. 1 shows an embodiment of the present invention. In FIG.
Portions corresponding to those in FIG. 2 are designated by the same reference numerals.

The present invention is characterized by a structure in which a level shifter 40 is provided on the input side of each signal receiving circuit 20 of each of the terminals 300A to 300N.

This example shows the case where the level shifter 40 is configured by a constant voltage diode, and if the voltage indicating the constant voltage characteristic of this constant voltage diode is, for example, 10V, if the amplitude of the signal input to the level shifter 40 exceeds 10V. A current flows through the receiving circuit 20, and a signal can be input to the receiving circuit 20.

Therefore, the amplitude of the output signal of the signal transmission circuit 10 of the main controller 200 is set to, for example, 12V, and the amplitude of the output voltage of the signal transmission circuit 10 of each of the terminal units 300A to 300N is selected to be 5V, which is the same as the conventional one. The signal receiving circuit 20 of the devices 300A to 300N receives the 12V signal output from the signal transmitting circuit 10 of the main controller 200, but the 5V signal output from the signal transmitting circuit 10 of each terminal device 300A to 300N is the main. It is only taken in by the signal transmission circuit 20 of the controller 200 and cannot enter the signal reception circuit 20 of each of the terminals 300A to 300N.

[Advantages of the Invention] As described above, since the signal transmission circuit 10 of each of the terminals 300A to 300N needs to drive only the signal reception circuit 20 of the main controller 200, it can be configured by an amplifier having a small power capacity.

Therefore, the signal transmission circuit of each of the terminals 300A to 300N can be composed of inexpensive parts, and thus each of the terminals 300A to 30N
0N can be manufactured at low cost, and this has the advantage that the entire signal transmission device can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, and FIG. 2 is a connection diagram for explaining a conventional technique. 100: two-wire signal transmission line, 200: main controller, 300A to 300N: terminal device, 10: signal transmission circuit, 20: signal reception circuit, 40: level shifter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriyuki Matsuda 5-6-12 Maehara-cho, Koganei-shi, Tokyo Incorporated company TAII Citizen Koganei Plant (56) Reference JP-A-59-40737 (JP, A)

Claims (1)

[Claims] 1. A main controller and a plurality of terminals are connected to a common balanced two-wire signal transmission line, and both ends of the balanced two-wire signal transmission line are short-circuited by terminating resistors, respectively, And a signal transmitting circuit in which each of the terminals is controlled by a data signal, and a pair of output terminals for outputting signals of opposite polarities are connected to a pair of transmission lines of the balanced two-wire signal transmission path, and A pair of input lines are connected to a pair of transmission lines of the balanced two-line signal transmission line, and a signal receiving circuit that outputs a binary signal in response to a voltage difference between the voltages applied to the pair of input lines is provided. In a signal transmission device that transmits and receives a data signal between the main controller and the plurality of terminals, a constant voltage diode is serially connected to the pair of input terminals of the signal reception circuit of each terminal with the same polarity. The main controller signal is The output (peak-to-peak) of the circuit is selected to be twice or more the constant voltage of the constant voltage diode, and the output amplitude of the signal transmission circuit of each terminal is selected to be the constant voltage or less. Signal transmission equipment.