JPH01119165A - Modem device - Google Patents

Abstract

PURPOSE:To prevent hit from being generated on a telephone line at the time of switching by controlling a relay by the output of first and second photoreceiving means coupled with first and second light emitting means, respectively, and performing the transfer of data between a modulation/demodulation circuit. CONSTITUTION:When a command to instruct connection to the telephone line is issued from a data terminal equipment 24 to an input/ output control circuit 16 after applying a power source on a modem device, the relay 22 is operated, and the telephone line is switched from a telephone set side to a modem device side. Next, when it is required to perform speech in voice by a telephone set in a communication state with the data terminal device of an opposite side, the handset of the telephone set is off-hooked. By performing such operation, a part of current on the telephone line flows on the second light emitting means 19, and the light emission of the means is detected by the second photoreceiving means 20, and by confirming the output of the photoreceiving means 20 by the input/output control circuit 16, the relay 22 is de-energized, then, a relay switch 12 is switched from the modem device to the telephone set side. In such a way, it is possible to switch the telephone line automatically without generating the hit.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a modem device having a telephone line switching circuit.

<Conventional Example> Recently, terminal devices such as personal computers (hereinafter referred to as PCs) have become widespread to the level of individuals, and so-called 10 communications using telephone lines are becoming widespread.

However, at the individual level, there is usually only one telephone line.
There is only a line, and it is used for telephone calls and 10 communications.

To connect a terminal such as a PC to a telephone line, a modem is used and the telephone is switched to the modem.

FIG. 2 shows an example of connecting a terminal to a telephone line. The phone is on-hook and line switching relay 1
is in a de-energized (off) state, and the relay switch 2 operated by this relay is connected to the telephone side contact 2a.

Further, the switch 3a operated by the line intermittent relay 3 is in a line connected state.

Now, when the handset of the telephone is picked up, that is, taken off-hook, the circuit switch 5 of the telephone is closed, and the telephone receives the carrier tone from the telephone line and becomes ready to talk.

On the other hand, to connect the telephone line to the modem side, operate the keys on the PC 6 and send an automatic dialing command to the line switching circuit 7.
The 0-line switching circuit 7 that sends the data to the transformer executes a predetermined program, energizes the relay 1, and switches and connects the relay switch 3 to the transformer side contact 2b. Thereby, the telephone line is connected to the modulation/demodulation circuit 4 via the isolation transformer 8.

In this case, if the telephone line is a digital line, it is necessary to send the telephone number of the other party as a pulse signal. PC
When a command signal is sent from 6 to the automatic dialing device 9 via the line switching circuit 7, the automatic dialing device 9 operates the relay 3t with a pulse output corresponding to the specified telephone number.
The relay switch 3a is turned on and off to generate a pulse signal at a rate of 10 or 20 pulses per second.

When the transmission of the telephone number of the other party is completed, the automatic dialing device 9 deenergizes the relay 3, and the switch 3a closes the telephone line. Therefore, when the other party responds, communication can be started.

Further, when the telephone line is an analog line, instead of energizing the relay 3, the automatic dialing device 9 sends a dual tone signal representing the telephone number of the other party to the telephone line via the modulation/demodulation circuit 4.

<Problem to be solved by the invention> However, if you wish to communicate by telephone during the 20-minute communication, you must end the 20-minute communication and switch the relay switch 2 to the telephone side by operating the keys on the PC. It needed to be done. In other words, the PC operator presses relay switch 2.
It is required to hold the handset of the telephone when changing the line, and if this is not done properly, the telephone line may be disconnected.

The present invention solves the above-mentioned drawbacks and provides a modem device that can switch between the modem device and the telephone automatically and without breaking the circuit.

<Means for Solving the Problems> The modem device of the present invention includes a modulation/demodulation circuit that is connected to a telephone line via an isolation transformer and modulates or demodulates transmitted and received data, and a modem device that selects between an isolation transformer and a telephone set for the telephone line. a first light-emitting means that emits light when the telephone line is closed; a resistor that is connected between the telephone line and the telephone and maintains the telephone line in a communication state; and a second light-emitting means that emits light when the telephone line is closed. a series circuit consisting of means, a first light receiving means and a second light receiving means optically coupled to the first light emitting means and the second light emitting means, respectively; controlling the relay and modulating/demodulating the relay by the output of the light receiving means; This is a modem device characterized by comprising an input/output control circuit that transmits and receives data to and from a circuit.

<Function> Modem device? After large input of ftft - terminal device 2
4 instructs the input/output control circuit 16 to connect to the telephone line, the relay 22 operates and the telephone line is switched from the telephone side to the modem device side.

This operation is confirmed by the input/output control circuit 16 when the first light receiving means 14 receives the light emitted from the first light emitting means 13 .

Next, when it becomes necessary to make a voice call using the telephone while in communication with the other party's data terminal device, the handset of the telephone is taken off-hook.

Due to this operation, a part of the current of the telephone line flows to the second light emitting means 19, and the second light receiving means 20 detects the light emission,
When the input/output control circuit 16 confirms the output of the light receiving means 20, it deenergizes the relay 22 and switches the relay switch 12 from the modem device to the telephone side. In other words, the telephone line is automatically switched without any momentary interruption. At this time, the series circuit of the current limiting resistor 18 and the second light emitting means 19 is almost short-circuited, so the light emitting means 19 stops emitting light, and the input/output control circuit 16 confirms the connection to the telephone.

After the telephone call is over, to switch back to the modem device side, operate the data terminal device 24 again and command the input/output control circuit V816 to switch the relay switch 12.

<Example> An example of the present invention will be described in detail using the accompanying drawings. One end 10a of the telephone line 10 is connected to a contact 12a of a relay switch 12 via a primary coil 11a of an isolation transformer 11. In addition to the telephone line 10, @10b is connected to the operating piece 12c of the relay switch 12 through the first light emitting means 13.
It is connected to the. The first light-emitting means 13 is constructed by connecting two light-emitting elements 13a and 13b in parallel, and oriented in opposite directions relative to the current. The first light emitting means 13 includes
An optically coupled first light receiving means 14 is provided. That is, the first light-emitting element 13a includes the first light-receiving element 14a.
are optically coupled to each other, and a second light receiving element 14b is optically coupled to the second light emitting element 13b. Each light receiving element 14a, 14b forms a series circuit with a resistor 15a, 15b and is connected between the ground and a DC power source, and its output is supplied to an input/output control circuit 16.

One end 17a of the telephone is connected to one end 10a of the telephone line, and the other end 17b is connected to a contact 12'b of the relay switch 12. A resistor 18 is connected between the other end 10b of the telephone line and the other end 17b of the telephone connected to the relay switch.
and a series circuit of the second light emitting means 19 are connected. The current limiting resistor 18 has a resistance value of several kilometres. Further, the second light emitting means 19 is constituted by a parallel connection circuit in which third and fourth light emitting elements 19a and 19b have opposite polarities. The second light emitting means 19 is optically connected to the second light receiving means 20,
The light receiving means 20 is constructed by connecting third and fourth light receiving elements 2Qa, 20b and resistors 21a, 21b in series. That is, the light receiving element 20a is optically coupled to the light emitting element 19a,
Further, the light receiving element 20b is optically coupled to the light emitting element 19b. A series circuit of light receiving elements 20a, 20b and resistors 21a, 21b is connected between ground and a DC power supply, and the output of each light receiving element is supplied to an input/output control surface 816, respectively.

The relay switch 12 is attached to the relay 22 and is switched according to the operation of the relay 22, and the operation of the relay 22 is controlled by the input/output control circuit 16.

The input/output control circuit 16 is connected to an external data terminal device 2.
The data sent from 4 is sent to the modulation/demodulation circuit 23, and the data input by the modulation/demodulation circuit 23 is sent to the data terminal device 24, and the program stored in the storage device (rtOM) 25 according to a command from the data terminal device 24. The relay 22 is controlled according to the following. In addition, when the relay switch 12 is switched to the extreme noise transformer 11 side, each input/output control circuit 16 selects a predetermined telephone number from the telephone directory stored in the data storage device (RAM) 26 in response to a command from the data terminal device. The number can be sent over the phone line.

Modulation and demodulation times! ! 823 is an analog-digital conversion circuit;
It has a modulation circuit and a demodulation circuit, and further has an adjustment circuit that sends out a digital signal or a tone signal depending on the nature of the telephone line.

The storage circuit 25 is composed of a ROM (read only memory) and stores a program regulating the operation of the modem device, which is executed by the input/output control circuit 16 in response to a command from the data terminal device 24.

The storage circuit 26 is composed of a RAM (random access memory) and stores telephone numbers, and the input/output control circuit 16 executes automatic connection to a predetermined telephone number in response to a command from the data terminal device 24.

The operation will be explained.

The circuit is in steady state and the telephone line is connected to the telephone. Thus, normal use of the telephone is possible, and when the telephone handset is picked up, ie, taken off-hook, the circuit switch 27 within the telephone closes and direct current flows through the telephone line. Assuming that a direct current is flowing from the telephone line 10a toward the isolation transformer 11, the light emitting element 13a of the first light emitting means 13 emits light, and the light receiving element 14a of the first light receiving means 14 controls the input/output of the output. The signal is sent to circuit 16. This causes the input/output control circuit 16 to confirm that the telephone line is available.

When the other party's telephone is off-book, the direction of the current flowing through the telephone line is reversed, the light emitting element 13b emits light instead of the light emitting element 13a, and the input/output control circuit detects this by the output of the light receiving element 14b. Make sure the phone line is busy.

In the steady state of the circuit, when the keyboard of the data terminal device is operated to send a command to the input/output control circuit 16 to connect the modem device to the telephone line, the relay 22 is energized and the relay switch 12 is connected to the isolation transformer 11 side. The zero input/output control circuit 16 connected to the contact 12a confirms the connection with the telephone line by the light emitted from the light emitting element 13a.

Connection to the other party's telephone is made using the data terminal device 24.
In response to a command from the input/output control circuit 16, the input/output control circuit 16 reads predetermined telephone number data from the RAM 26 and sends it to the modulator M23. When applied to the next coil 11b, a telephone number signal is sent to the telephone line. Also, when sending the telephone number as a pulse signal to the telephone line, the input/output control circuit! ! 816 is RAM-2
The relay 22 is operated in accordance with the data read from the terminal 6 to turn the relay switch 12 on and off, thereby generating a pulse signal representing a telephone number.

When the other party's telephone goes off-hook, the polarity of the direct current flowing through the telephone line changes, and the light emitting element 13b emits light,
Check that communication is possible.

When a modem device is connected to the telephone line, when the telephone is taken off-hook, i.e., when switch 27 is closed, a portion of the current flowing through the telephone line passes through resistor 18 and the second
The light flows through the light emitting means 19 and causes the light emitting element 19b to emit light. The magnitude of this shunt current is approximately determined by the ratio between the impedance of the primary coil lla of the isolation transformer 11 and the resistance value of the resistor 18. The light emitted from the light emitting element 19b is detected by the corresponding light receiving element 20b. When the input/output mII control circuit 16 confirms the light receiving output of the light receiving element 20b, the RO
The relay 22 is deenergized according to the program stored in the M25, and the relay switch 12 is switched to the contact 12b on the telephone side. This makes it possible to make phone calls. In this state, both ends of the series circuit of the resistor 18 and the light emitting means 19 are almost short-circuited, and the communication current flows through the light emitting means 13. When the modem device is connected to the telephone line again, a switching command for the relay switch 12 is sent to the input/output control device 16 by operating the keyboard of the data terminal device 24 again.

The light emitting element 19a of the light emitting means 19 reverses the polarity of the telephone line when the communication partner turns on the telephone, so by detecting the light emitted by the light receiving element 20a, the input/output control device 16 confirms the end of communication. do.

Effects> Since the present invention has the above-described configuration, switching from a modem device to a telephone is automatically performed, and there is no momentary disconnection of the telephone line at the time of switching. There is no need to hold it, and no data errors occur due to instantaneous interruptions.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a modem device according to the present invention, and FIG. 2 is a circuit configuration diagram of a conventional example. In the figure, 10a and 10b are telephone lines, 11 is an isolation transformer, 12 is a relay switch, 13.19 is a light emitting means, 13
a, 13b, 19a, 19b are light emitting elements; 14.20 is a light receiving means; 14a, 14b. 20a and 20b are light receiving elements, 16 is an input/output control circuit, 1
8 is a resistor, 22 is a relay, 23 is a modulation/demodulation circuit, 24 is a data terminal device, 25 is a ROM, 26 is an I"tAM
It is. Patent applicant Murata Manufacturing Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] 1. A modulation/demodulation circuit connected to a telephone line via an isolation transformer to modulate or demodulate transmitted and received data, a relay having a switch for selectively connecting the isolation transformer and the telephone to the telephone line, and the telephone. a series circuit consisting of a first light emitting means that emits light when the line is closed, a resistor connected between the telephone line and the telephone set and maintaining the communication state of the telephone line, and a second light emitting means; and first and second light emitting means optically coupled to the second light emitting means.
A modem device comprising: a light receiving means; and an input/output control circuit that controls the relay using the output of the light receiving means and transmits and receives data to and from the modulation/demodulation circuit.