JPH03268598A - Malfuction preventing circuit - Google Patents

Abstract

PURPOSE:To remove the generation of malfunction due to noise by finding out AND between a signal outputted from the strobe output terminal of a multifrequency code receiver for inputting a dialing signal from a communication line and a signal obtained by delaying the signal by a delay circuit to obtain a strobe signal. CONSTITUTION:A dial signal from a telephone line (communication line) 10 is inputted to the multifrequency code receiver 11. The strobe output of the receiver 11 is inputted to one input terminal of an AND circuit 12 and the input terminal of a delay circuit 13. When noise is included in a signal sent from a telephone line 10 or noise is independently sent, a pulse with a short pulse width may be generated prior to a true strobe. When the delay time of a delay circuit 13 is set up to a value slightly larger than the time corresponding to the short pulse width, both the input terminals of the circuit 12 are turned to 'H' after the lapse of the delay time of the circuit 13 from the generation of the true strobe, so that the pulse corresponding to the unnecessary pulse with the short pulse width does not appear on the output of the circuit 12.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a malfunction prevention circuit for error-free decoding of a dialing signal sent from a caller, and is capable of ensuring that a dialing signal sent in a multi-frequency code is received at a telephone office. The purpose of the present invention is to provide a malfunction prevention circuit capable of decoding in The configuration is such that the strobe signal is obtained by logically multiplying this signal with a signal delayed by a delay circuit.

[Industrial application field]

The present invention relates to a malfunction prevention circuit for error-free decoding of a dialing signal issued by a calling party.

[Conventional technology]

Until recently, telephone dialing was done using a rotary dial, but in recent years it has become mainstream to use a so-called touch-tone phone. These telephones are equipped with multi-frequency codes, so-called DTMF, to send dial signals to the central office so that the signals can be reliably identified.

FIG. 4 is a block diagram of a conventional system including a multi-frequency code receiver provided at a telephone office for decoding dial signals. In the figure, the multi-frequency code receiver 1 includes, for example, one
Local lines are connected and incoming dial signals are input.

The multifrequency code receiver 1 includes a bandpass filter, an amplitude detector, a clock generator, a timing circuit, a decoder, a register, and other electronic circuits, and outputs 4-bit data. When the value has settled down to a reliable value, it outputs a strobe to encourage the data to be captured. and,
The multi-frequency code receiver 1 is integrated into an IC and receives DTMF (DTMF)-
The configuration is similar to that of commercially available decoders.

The 4-bit data output is input to the input terminal of a 4-16 line decoder 2, and the strobe is input to the 4-16 line decoder 2.
-16 It is input to the strobe input terminal of the line decoder 2. The output of the 4-16 line decoder 2 (
16 ways) are input to the data processing device 3. As this data processing device 3, a board computer or the like having a CPU, ROM, RAM, parallel input port, etc. can be used. In that case, the output of the 4-16 line decoder 2 is transferred to a parallel input port. is input.

However, for example, if the dial number "1" is specified by the caller's operation, in the case of DTMF, the low group 697Hz and the high group 1
A dual tone with 209 Hz is emitted from the telephone and the signal reaches the multi-frequency code receiver 1. Then, signal processing is performed in the multi-frequency code receiver, and the 4-bit data is outputted in order from the MSB side.
0001" appears. At about the same time, the strobe is output. As a result, the "0001°
is taken into the 4-16 line decoder 2.

As a result, one of the 16 output lines of the 4-16 line decoder 2 changes state.

That is, for example, it changes from "L" to "HII". Therefore,
The CPU of the data processing device 3 can now determine which bit of the parallel input port has changed state. Since it is known which bit state change corresponds to how many dialed numbers, it can be determined that the calling party has sent the dialed number "1". In the same way, when the dial numbers that are sent one after another are known and the caller's dialing operation is completed, the dial numbers that are sent are referenced and an attempt is made to connect the caller's line to the corresponding line. A control signal is sent to the illustrated exchange. and,
The lines will be connected and you will be able to make calls.

[Immediate problem that the invention seeks to solve]

By the way, the multi-frequency code receiver 1 is connected to the calling party's telephone.
Before the signal reaches , for example, car ignition noise, noise from neon sign equipment, thunder noise, etc. enter the line, and white noise or impulsive noise mixes into the dual tone signal. or noise may get onto the line. As a result, the dial number from the caller is not correctly decoded by the 4-16 line decoder 2, resulting in a malfunction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a malfunction prevention circuit that allows a telephone office device to reliably decode a dialing signal sent in a multi-frequency code.

[Means to solve the problem]

FIG. 1 is a principle block diagram illustrating the malfunction prevention circuit of the present invention. In the same figure, telephone line (communication line)
The dial signal from 10 is input to a multi-frequency code receiver 11. The strobe output of the multi-frequency code receiver 11 is input to one input terminal of an AND circuit 12 and an input terminal of a delay circuit 13. The output of the delay circuit 13 is input to the other input terminal of the AND circuit 12. Further, the multi-frequency code receiver 11 outputs, for example, 4-bit data as data output.

[For production]

If noise is added to the signal sent from the telephone line 10 or if noise is sent alone, a pulse with a short pulse width may be emitted before the true strobe. If the delay time of the delay circuit 13 is set to be slightly larger than the time corresponding to the short pulse width, both input terminals of the AND circuit 12 become "H" exactly when the true strobe This occurs after the delay time of the delay circuit 13 has elapsed since the issuance of the pulse, and a pulse corresponding to the above-mentioned unnecessary short pulse width does not appear at the output of the AND circuit 12.

That is, the false strobes caused by noise disappear, and only the true strobes can be obtained as the output of the AND circuit 12. Therefore, by using this strobe to input data into a decoder or the like, malfunctions caused by noise can be prevented.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a circuit block diagram including the malfunction prevention circuit of the present invention. In the figure, a dial signal from a telephone line 10 is input to a multi-frequency code receiver 11. The strobe output of the multi-frequency code receiver 11 is input to one input terminal of an AND gate 14 and the input terminal of an inverter 15 in the delay circuit 13, and the output of the inverter 15 is input to an inverter 17 via a resistor 16. Input to the input terminal.

The output of the inverter I7 is input to the other input terminal of the A, ND gate 14, and the input terminal of the inverter 17 is grounded via a capacitor I8. The multi-frequency code receiver 11 has a 4-bit data output terminal, which is input to the data input terminal of the 4-16 line decoder 2.

The output of the AND game) 14 is input to the strobe input terminal of the 4-16 line decoder 2.
The output of the -16 line decoder 2 is input to the parallel input port of the data processing device 3.

However, if noise is added to the signal sent from the telephone line 10, or if noise is sent alone, a pulse with a short pulse width is emitted before the real strobe as shown in FIG. If the delay time of the delay circuit 13 is set to be slightly larger than the time corresponding to the short pulse width, both input terminals of the AND gate 14 become "H" just as After the delay time τ of the delay port 813 has elapsed since the true strobe was emitted, a pulse corresponding to the unnecessary short pulse width does not appear at the output of the AND gate 14. That is, Although the false strobe caused by noise disappears and is delayed by the delay time τ, only the genuine strobe can be obtained at the output of the AND gate 14. Therefore, this strobe is used to transmit data to a decoder, etc. Malfunctions due to noise can be prevented by incorporating the short pulse width into the strobe pulse.Since the pulse width of the short pulse width is sufficiently short compared to the true strobe pulse, the delay time does not pose any practical problem. It won't happen.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to avoid malfunctions caused by noise when decoding an output signal from a multi-frequency code receiver, which often occurred in the past. As a result, it is possible to obtain a malfunction prevention circuit that can decode dialing signals sent from a line in a multi-frequency code without error.

[Brief explanation of drawings]

FIG. 1 is a principle block diagram explaining the malfunction prevention circuit of the present invention, FIG. 2 is a circuit block diagram including the malfunction prevention circuit of the present invention, and FIG. 3 is a time chart explaining the present invention in detail. 1 is a conventional block configuration diagram including a multi-frequency code receiver provided at a telephone office for decoding dial signals. 10... Communication line, 11... Multi-frequency code receiver, 12... AND circuit, 13... Delay circuit.

Claims (1)

[Claims] It has a multi-frequency code receiver (11) into which a dial signal from a communication line (10) is input, and the multi-frequency code receiver (11)
1. A malfunction prevention circuit characterized in that a strobe signal is obtained by performing an AND operation between a signal output from a strobe output terminal of the circuit (1) and a signal delayed by a delay circuit (13).