KR890003493Y1 - Modem switch hook detector circuit - Google Patents

Abstract

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Description

Switch hook detection circuit of a modem for an aerial line (exchange line)

Figure is an overall configuration diagram of a modem to which the present invention is applied.

* Explanation of symbols for main parts of the drawings

1: modulator 2: demodulator

3: 4-wire / 2-wire hybrid circuit 4: Ring detector

L ₁ , L ₂ : Telephone line connection terminal L ₃ , L ₄ : Telephone connection terminal

R ₁ , R ₂ , R ₃ : Resistance D _{1 to} D ₄ : Diode

U ₁ : Microprocessor OC ₁ : Optocoupler

The present invention relates to a switch hook detection circuit for informing a microprocessor of a modem of a manual call and a manual response state when a telephone is connected to an aerial (switch circuit) modem.

Among the modems that use 2-Wire Full Duplex, the frequency division mode modem must recognize whether it is in call or answer state to maintain transmission of incoming and outgoing signals.

Conventionally, when a telephone is connected to a data transmission modem to make a mutual voice call, that is, a manual call and a manual answer, the microprocessor for system control of the modem has its own manual state (manual call state and manual answer state). ) To distinguish between data communication and voice call and to maintain mutual transmission path. In the conventional apparatus, a microprocessor such as model number 8085 was used to perform this function, and the hook switch of the telephone was turned on during manual call as a means for recognizing the above-mentioned manual call and manual response state to the microprocessor. As a result, the loop current flowing through the telephone is induced to the relay coil, and by the operation of this relay contact, a predetermined signal is supplied to the microprocessor to indicate that the modem is in a manual call state. The detector detects and supplies a signal to the microprocessor, indicating that it is in passive response.

Here, using a relay to detect the loop current flowing to the telephone when making a manual call is mechanical and expensive. It is not only economical, but also the noise of the relay contact on and off during operation can cause the microprocessor to malfunction. There is a problem in that the lack of reliability and stability of the product.

Accordingly, an object of the present invention is to provide a switch hook circuit that detects the looping current of a telephone by using a semiconductor device to solve the above-mentioned drawbacks and provides a reliable detection operation, response speed, and low cost. By supplying as to be able to recognize the manual call or manual response state, the present invention will be described in detail based on the accompanying drawings as follows.

Figure shows a schematic configuration of a modem to which the switch hook detection circuit of the present invention is applied.

In general, a data transmission modem using a two-wire full-duplex system includes a modulator 1 and a demodulator 2, a four-wire / two-wire hybrid circuit 3, and a microprocessor U ₁ for system control of the modem. The modem and telephone line are mutually coupled by an impedance matching transformer T ₁ .

Here, the telephone for the manual call and the manual answer is connected in parallel with the connection terminals L ₁ and L ₂ of the telephone line, and the ring detector 4 is provided to detect the ring signal input from the telephone line and provide it to the microprocessor U ₁ . Are connected in parallel.

Switch-hook detection circuit of the present design has been indicated by a broken line block (a) part of the figure, to sense the loop current of the telephone line connected to telephone detected by the resistance R ₁ and the resistance R ₁ is connected in series to one side of the telephone line When the connected current is connected to the diode bridge circuit (D ₁ , D ₂ , D ₃ , D ₄ and the resistor R ₂ ) so that the current can form a current path in a certain direction, the current flows in the circuit. And a signal output stage having an optocoupler OC ₁ for supplying a corresponding logic level signal to the microprocessor U ₁ .

Zener diode D ₅ is here to protect optocoupler OC ₁ from overcurrent in the circuit.

In the circuit as described above, the operation of notifying that the modem is in a manual call state by detecting the loop current of the telephone is as follows.

Assume that a telephone line is connected to the modem's telephone line terminals L ₁ and L ₂ , and that the telephone is connected to the telephone terminals L ₃ and L ₄ connected in parallel with this terminal, and that the user's handset For example, the hook switch is turned on, a telephone line and a loop are formed, and current flows by the DC power supplied from the exchange side. This current flows through the resistor R ₁ to the phone, part of which flows through the diode D ₁ (or D ₃ ) of the diode bridge to the resistor R ₂ , where the photo transistor is turned on as the photodiode of the optocoupler OC ₁ is turned on. . This causes the collector signal output stage of the phototransistor of optocoupler OC ₁ to drop to zero potential from the power supply Vcc potential and the collector's zero potential signal is passed to microprocessor U ₁ to indicate that the modem is in manual call.

Current through optocoupler OC ₁ flows into diode D ₄ (or D ₅ ) to form another current loop similar to the current loop of the telephone. In this case, since the polarities of the connection terminals L ₁ and L ₂ of the telephone line may be reversed, both currents may flow in a predetermined direction by the diode bridles D ₁ , D ₂ , D ₃ , and D ₄ .

Also, when an overcurrent flows to the optical coupler OC ₁ is formed by a zener diode D _5, another current loop will protect the optical coupler OC _1.

As described above, when the switch hook state of the telephone is detected and the signal is transmitted to the microprocessor U ₁ , the modem is in the passive state. The voice communication by the telephone is terminated, and the front panel switch of the modem is used for data communication. (5) When pressed, microprocessor U ₁ drives relay K ₁ again and contacts relay S ₁ of this relay connect the telephone line to transformer T ₁ of the modem. When the telephone line is connected via the transformer T ₁ , the modem's modulation (1) and demodulator (2) operate to enable data transmission.

On the other hand, when the ring detector 4 detects a ring signal from the telephone line and transmits the detection signal to the microprocessor U ₁ , the modem is in a passive response state, and then the user makes a call by the telephone. Control the telephone line.

As described above, according to the detection circuit of the present invention, a stable circuit element is used to ensure a reliable response and enable the modem to recognize a manual call or a manual response state. There is an advantage that can be used by connecting the phone regardless of the power supply.

Claims (1)

Modulator (1) and demodulator (2) for data transmission and reception, 4-wire and 2-wire hybrid circuit (3), microprocessor U ₁ for system control, and ring signal flowing through the telephone line are detected and signal to micro processor U ₁ In a modem for an aerial (switching line) having a ring detector (4) for supplying a switch and a switch hook detection circuit for detecting a switch hook state by a telephone and supplying the detection signal to the microprocessor U ₁ , parallel to the telephone. A diode bridge connected so that the resistance (R ₁ ) connected in series with one side of this telephone line and the current detected at this resistance (R ₁ ) form a current path in a certain direction to sense the loop current of the connected switching line. Circuits (D ₁ , D ₂ , D ₃ , D ₄ and resistor R ₂ ), and the bridge circuits are coupled to the logic corresponding to the current flow through the circuits to provide a level signal to the microprocessor U. _A switch hook detection circuit for a modem for an aerial line (switched line), comprising a signal output stage including an optical coupler OC ₁ for supplying to ₁ .