JPH0793605B2 - Interference prevention circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to an interfering radio wave prevention circuit in a system in which a plurality of second devices are connected to a first device, for the purpose of preventing the occurrence of interfering radio waves. An interfering radio wave prevention circuit used in a system configured by connecting a device and a plurality of second devices by a signal line, and generating a connection signal indicating that the device is connected to the second device side. A connection signal generating circuit, a connection signal receiving circuit that receives a connection signal from the connection signal generating circuit on the first device side, and a switch that disconnects the signal connection to the second device according to the output of the connection signal receiving circuit. Each circuit is provided and configured.

TECHNICAL FIELD The present invention relates to an interference wave prevention circuit in a system in which a plurality of second devices are connected to a first device.

In a system in which a plurality of second devices are connected to the first device, for example, a star connection network system or the like, the device may malfunction due to generation of jamming radio waves. In recent years, interference waves generated from devices including electronic circuits have become a social issue, and legal restrictions on interference waves are also being considered.

[Prior Art] FIG. 3 is a diagram showing the configuration of a one-to-many connection system (star network system) in which a plurality of second devices are connected to a first device. A first device 1 and a plurality of n second devices 2 are star-connected via a signal line 3. The first device 1 and the second device 2 are connected to the signal line 3
Signals are exchanged via.

In this type of system, in addition to the radio waves generated from the main bodies of the devices 1 and 2, radio waves are also generated from the signal line 3, and these radio waves act as interfering radio waves to cause the devices 1 and 2 to malfunction and are not shown. Malfunction other electronic devices including completely unrelated electronic circuits. Conventionally, in order to prevent the generation of such jamming radio waves, a magnetic material is used as a housing (frame) of each device, or an internal circuit is covered with a magnetic material.

[Problems to be Solved by the Invention] Generation of radio waves from the apparatus body can be suppressed to some extent by applying the above-described measures. However, no treatment is applied to the signal line 3 connecting the device 1 and the device 2. The signal line 3 or the circuit pattern acts as an antenna and scatters radio waves around. Especially, for example, even when the first device 1 and the first (# 1) second device 2 are communicating, the remaining signal lines (# 2 to #n
Since (1) to (3) are not used (the power is off), they remain as they are, so that a high frequency signal flows through these signal lines 3 to generate a radio wave. For this reason, a problem still occurs due to the generation of jamming radio waves.

The present invention has been made in view of such points,
It is an object of the present invention to provide an interference wave prevention circuit that can prevent generation of interference waves.

[Means for Solving Problems] FIG. 1 is a block diagram showing the principle of the present invention. The same parts as those in FIG. 3 are designated by the same reference numerals. In the figure, 2a is a connection signal generation circuit for generating a connection signal indicating that it is connected, and is included in the second device 2, and its output is output via the second signal line 3b to the second signal line 3b. 1 to device 1. 1a is a connection signal receiving circuit that receives a connection signal from the connection signal generating circuit 2a, and 1b is a disconnection circuit that disconnects the signal connection to the second device 2 according to the output of the connection signal receiving circuit 1a. The separation circuit 1b is connected to the first signal line 3a.

As described above, the first (# 1) second device 2 and the first device 1
I explained the connection relationship with, but this relationship remains (#
The same applies to the connection relationship between the second device 2 and the first device 1 of 2 to #n).

[Operation] When the first device 1 and the second device 2 are connected, a connection signal is sent from the connection signal generation circuit 2a to the connection signal reception circuit 1a via the signal line 3b. Connection signal receiving circuit 1a
Receives this connection signal and gives it to the disconnection circuit 1b, and the disconnection circuit 1b maintains the connection with the signal line 3a when receiving the connection signal. Next, when the first device 1 and the second device 2 are not connected (for example, when the signal line 3 is disconnected and when the second device 2 is connected).
When the power of the device 2 is off), the connection signal is not given from the connection signal generating circuit 2a to the connection signal receiving circuit 1a. When the disconnecting circuit 1b receives the signal from the connection signal receiving circuit 1a and finds that the first device 1 and the second device 2 are not connected, it disconnects the connection with the signal line 3a. At the same time, the potential of the signal line 3a is held at 0 potential. As a result, the high frequency signal is not superimposed on the signal line 3a, so that it is possible to prevent the occurrence of jamming radio waves.

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

FIG. 2 is an electric circuit diagram showing an embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals. On the side of the second device 2, the connection signal generating circuit 2a is composed of a buffer G1. The input of the buffer G1 is grounded. 2b is an electronic circuit for the second device 2 to perform its original function.

On the side of the first device 1, the ground signal receiving circuit 1a comprises a buffer G2 and a pull-up resistor R1 connected to its input line. The buffer G2 is connected to the buffer G1 via the signal line 3b. Isolation circuit 1b is a buffer
3-state buffer G3 that receives the output of G2 as a control signal
And a pull-down resistor R2 connected to its output line. A signal is connected to the input of the buffer G3, and its output enters the electronic circuit 2b via the signal line 3a. The operation of the circuit thus configured will be described below.

First, a case where the second device 2 exchanges signals with the first device 1 will be described. In this case, buffer G1
Since its input is grounded, its output is "0", and this "0" becomes a connection signal and enters the buffer G2 via the signal line 3b. As a result, the buffer G2 gives a "0" signal to the 3-state buffer G3. The control signal entered as "0" in the 3-state buffer G3 makes the 3-state buffer G3 active (operating state). As a result, the signal input from the input is output as it is from the three-state buffer G3 and given to the electronic circuit 2b via the signal line 3a. The electronic circuit 2b receives the input information and performs necessary processing.

Then, as a result of the necessary processing, when it becomes necessary to send information to the first device 1 side, the information is sent to the first device 1 side via the bidirectional signal line 3a by a transmission circuit (not shown). To send. The first device 1 side receives the information sent from the second device 2 side and performs a predetermined process.

Then, the power of the second device 2 is turned off and the first device 1 is turned off.
The case where no signal is exchanged with will be described.
In this case, the output of the buffer G1 is in a floating state and the potential is not fixed. However, the buffer
Since the pull-up resistor R1 is connected to the input line of G2, its input level is fixed at "1". Then, the buffer G2 gives a "1" signal to the 3-state buffer G3. Three
The control signal "1" entered in the state buffer G3 puts the output of the three-state buffer G3 in a high impedance state (inoperative state). Therefore, as it is, the signal line 3a
Since the potential of F2 floats, pull down resistor R2 to the line.
Are connected to fix the signal line 3a to "0". Moreover, 3
Since the signal that has entered the state buffer G3 does not appear on the output side, the signal line 3a does not function as an antenna to generate an interfering radio wave. The potential of the signal line 3b side is also "1".
Since it is fixed to, and high frequency signals do not overlap, no interfering radio waves are generated.

When the signal lines 3a and 3b are not connected, the signal lines 3a and 3b do not exist in the first place, and therefore it is impossible to generate radio waves as an antenna. In this case, the first
The pattern from the output of the 3-state buffer G3 of the device 1 to the connection point of the signal line 3a may serve as an antenna and generate a radio wave. However, since the input of the buffer G2 is kept in the "1" state by the pull-up resistor R1, the 3-state buffer G3 which receives the "1" signal as a control signal is in the high impedance state and prevents the signal from overlapping the pattern. . Moreover, the potential of this pattern is fixed at "0" by the pull-down resistor R2.

In the above description, the connection signal generation circuit 2a, the connection signal reception circuit 1
Although a circuit including a buffer and a resistor is used as a and the separation circuit 1b, the circuit is not limited to such a circuit, and a circuit having another configuration can be used. That is, the connection signal generation circuit 2a may be any circuit as long as it can transmit a connection signal indicating that it is connected to the first device 1 side, and the connection signal reception circuit 1a may be any circuit as long as it receives the connection signal sent and gives it to the disconnection circuit 1b, and the disconnection circuit 1b makes a signal connection with the signal line 3a when the connection signal does not come. Any circuit may be used as long as it can be separated.
Further, the connection between the first device and the plurality of second devices is not limited to the star connection.

[Effects of the Invention] As described in detail above, according to the present invention, in a system in which a first device and a plurality of second devices are connected, a connection signal transmitted from the second device By disconnecting the signal connection to be placed on the signal line from the first device depending on the presence or absence, it is possible to provide a jamming wave prevention circuit capable of preventing the occurrence of jamming waves.

[Brief description of drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is an electric circuit diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing the configuration of a star-type network system. In FIG. 1, 1 is a first device, 1a is a connection signal receiving circuit, 1b is a disconnecting circuit, 2 is a second device, 2a is a connection signal generating circuit, and 3 is a signal line.

Claims (1)

[Claims] 1. A jamming prevention circuit for use in a system comprising a first device and a plurality of second devices connected by a first signal line, the self-connecting device being connected to the second device side. A connection signal generating circuit for generating a connection signal indicating that the connection signal from the connection signal generating circuit is transmitted to the first device side.
And a switching circuit for disconnecting the signal connection to the second device according to the output of the connection signal receiving circuit. The connection signal receiving circuit is provided in the second device. The interfering radio wave prevention circuit, characterized in that the switching circuit disconnects the first signal line and holds the potential of the first signal line at 0 potential when it is detected that they are not connected.