JPH0149064B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a two-way communication system that enables two-way communication between a plurality of terminal devices connected to one signal cable.

[Background technology]

Recently, with the development of home automation and office automation, multiple terminal devices are branching and connecting intercom signals, video signals such as cable TV, security information such as crime prevention or disaster prevention, etc. to a single signal cable. A two-way communication system is being considered that allows communication between two parties. Figure 1 shows an example of a contention type two-way communication system.
Keying) A terminal device that sends out a modulated transmission signal V _T , 2 is a transmission signal V _T from each terminal device 1A to 1D
It is a central control device equipped with a converter section 2a that sends out a return signal _VB obtained by converting the carrier frequency _f1 into _f2 .
is connected via a branch 4 to a signal cable 3 made of a coaxial cable, optical fiber, or the like.
The central control device 2 also has one of the terminal devices 1.
When a transmission signal from A to 1D is received, a transmission suppression signal V ₀ of carrier frequency f ₀ is sent out to suppress transmission signals from terminals 1A to 1D other than the terminal 1A to 1D for a certain period of time. Transmission suppression unit 2
b is provided. On the other hand, each of the terminals 1A to 1D is provided with a data receiving section configured to receive the data of the return signal _VB when the return signal _VB containing address data matching the own address is received. Two-way communication is performed between the terminals 1A to 1D via the central control device 2. In the figure, 5 is a television camera, 6 is an intercom device, and the signal cable 3 is also used as a signal transmission line of the television intercom system.

Now, when transmitting data from the terminal device 1A to the terminal device 1D, first, a transmission signal V _T containing address data for calling the terminal device 1D from the terminal device 1A is transmitted.
Send out. In response to this transmission signal V _T , the converter section 2a of the central control device 2 converts this transmission signal into
By converting the carrier frequency of V _T (f ₁ →f ₂ ), a return signal V _B is formed and sent to the signal cable 3. The terminal device 1D that receives the return signal V _B containing the address data that matches its own address sequentially captures the data of this return signal V _B.
A data transmission circuit line or a speech line is set between the terminal devices 1A and 1D. Here, as shown in FIG. 2, the period (t ₁ - t ₂ ) set by the time clock sent from the central controller 2
When the transmission signal V _T from the terminal device 1A is received, the transmission suppression signal V ₀ of the transmission suppression unit 2b of the central control device 2 is sent out, and the transmission signal V _T is sent from the other terminal devices 1B to 1D. is suppressed, and a communication line is set up between the terminals 1A and 1D during the period (t ₂ -t ₃ ) determined by the time clock. However, in such a conventional example, the terminal device 1A
sends the transmission signal V _T and then other terminal devices 1B~
A transmission signal V T is sent from another terminal (for example, 1B) during the period (ΔT) from when 1D receives the transmission suppression signal _{V 0} to when transmission is suppressed, that is, until the communication line is secured. In this case, the transmission signal V _T to the terminal device 1B cannot be suppressed by the transmission suppression signal V ₀ , and the terminal devices 1A and 1B will send out the transmission signal V _T at the same time, resulting in an interference state and an error. There was a risk that data would be transmitted and the system would malfunction.

[Purpose of the invention]

The present invention has been made in view of the above points,
The purpose is to provide a two-way communication system that can reliably determine the presence or absence of interference in transmitted signals and prevent malfunctions when transmitted signals are sent simultaneously from multiple terminals. be.

[Disclosure of the invention]

(Embodiment) FIG. 3 is a block circuit diagram of terminal devices 1A to 1D according to an embodiment of the present invention, and the overall configuration and operation are substantially the same as the conventional example shown in FIG. Reference numeral 10 denotes an information output circuit that outputs information data to be transmitted, and the information data to be transmitted includes address data, control data, etc. of the terminal devices 1A to 1D to be called. Input from the keyboard. 11 is an encoder 12 and a clock generator 1
3, which generates a data signal VD consisting of a baseband signal based on the data output from the information output circuit 10 and the clock _{VCL .}
form. 14 is a modulation circuit that performs FSK modulation on the carrier wave Vf ₁ with the data signal V _D , 15 is a gate circuit, and a suppression signal detection output from the suppression detection circuit 16 that detects the transmission suppression signal V ₀ sent from the central control device 2. It is designed to be closed when obtained. 17 is a hybrid circuit, 18 is a switch circuit for switching between transmission and reception;
is switched to the a side at the time of calling, and normally switched to the b side. 19 is the received return signal V _B
a demodulator that performs FM detection and demodulates the data signal _VD ,
Reference numeral 20 denotes an address determiner, which outputs an address match signal V _A that opens the AND gate ₂₁ when the received return signal V B includes address data that matches its own address. 22 is an information receiving circuit that appropriately processes and stores the data taken in through the AND gate 21 and generates a load control signal; A data receiving section 23 is formed by the information receiving circuit 22 and the information receiving circuit 22 . 2
4 is an AM detector that performs AM detection on the received return signal _VB ; 25 is a waveform shaping circuit that converts the output of the AM detector 24 into a digital signal; and 26 is an output of the waveform shaping circuit 25 that is synchronized with the clock _VCL . The AM detector ₂₄ , the waveform shaping circuit 25, and the comparison/discrimination circuit 26 form an interference discrimination section 27, which detects the amplitude caused by interference. Interference is determined by detecting modulation components. This interference detection signal
V _M is input to the information output circuit 10, and the information output circuit 10 recognizes the occurrence of interference due to the input of the interference detection signal V _M , and the information output circuit 10 recognizes the occurrence of interference and provides information for an arbitrary time (a random time controlled by the output of the random number generation means). Stop outputting data and wait.

The operation of the embodiment will be specifically explained below. Now, the terminal device 1A sends out a transmission signal _VTA as shown in FIG _. When a transmission signal V _TB as shown in b in the same figure is sent from 1B, both transmission signals
Parts T ₁ and T ₂ where V _TA and V _TB have different frequencies due to interference
In the area where the data differ, a bead due to interference appears as an amplitude modulation component as shown in c of the same figure. The frequency of this amplitude modulation component is FSK
It is twice the shift frequency Δf in modulation, and is also included in the return signal V _B frequency-converted (f ₁ →f ₂ ) by the converter section 2a of the central control device 2. A.M.
This amplitude modulation component is detected by the detector 24 as shown in d in the figure, and this detected output V _AM is sent to the waveform shaping circuit 2.
5 into a digital signal V _AM '. Next, a comparison/determination circuit 26 determines whether this digital signal V _AM ' is obtained in synchronization with the H level period of the clock V _CL and outputs an interference detection signal V _M . Here, the interference detection signal V _M is output when an amplitude modulation component is detected in synchronization with the clock V _CL that forms the data signal V _D , and during the L level period of the clock V _CL . The noise pulse P _N caused by the obtained noise signal V _N can be reliably removed, and an erroneous interference detection signal V _M will not be obtained. Next, when this interference detection signal V _M is input to the information output circuit 10, the information output circuit 10 stops outputting the information data for an arbitrary period of time, stops transmitting the data, and after an arbitrary period of time elapses, transmits the transmission signal again. Send V _T. At this time,
Since the transmission stop times of the terminals 1A and 1B are different from each other, the transmission signals V _TA and V _TB are never sent out simultaneously from the terminals 1A and 1B again, and malfunctions due to interference do not occur.

〔Effect of the invention〕

As described above, the present invention includes a large number of terminal devices that transmit a transmission signal in which a carrier wave is FSK-modulated with a data signal including address data, and a return signal that is obtained by converting the carrier frequency of the transmission signal from each terminal device. data that is branch-connected to a central control unit equipped with a converter section to one signal cable, and when a return signal containing address data that matches the own address is received, the data of the return signal is captured. In a two-way communication system in which a receiving section is provided in each terminal device, an interference discrimination section is provided in each terminal device for determining the presence or absence of interference by detecting the amplitude modulation component of a received return signal. The data transmission is stopped by the interference detection signal output from the terminal, and the amplitude modulation component of the return signal that occurs when multiple terminals transmit signals is detected and interference is detected. Since the presence or absence of interference is determined, the presence or absence of interference can be reliably detected, and data transmission is stopped in response to an interference detection signal, which prevents system malfunctions due to erroneous data transmission. It has the advantage of being able to

[Brief explanation of drawings]

Fig. 1 is a diagram showing a schematic configuration of a two-way communication system according to the present invention, Fig. 2 is an explanatory diagram of the same operation as above, Fig. 3 is a main block circuit diagram of an embodiment of the present invention, and Fig. 4 is same as above. FIG. 1A to 1D are terminal devices, 2 is a central control device, 2a
3 is a converter section, 3 is a signal cable, 23 is a data receiving section, and 27 is an interference discrimination section.

Claims (1)

[Scope of Claims] 1. A large number of terminal devices that transmit a transmission signal in which a carrier wave is FSK-modulated with a data signal including address data, and a return signal that is obtained by converting the carrier frequency of the transmission signal from each terminal device. A data reception system in which a central control unit equipped with a converter section is branch-connected to a single signal cable, and when a return signal containing address data that matches the own address is received, the data of the return signal is captured. In a two-way communication system, each terminal is provided with an interference discrimination section that determines the presence or absence of interference by detecting the amplitude modulation component of a received return signal. A two-way communication system characterized in that data transmission is stopped in response to an output interference detection signal. 2. According to claim 1, the interference determination section is formed so that an interference detection signal is output when an amplitude modulation component is detected in synchronization with a clock forming a data signal. Two-way communication system.