KR920011066B1 - Interface circuit of dial signal - Google Patents

Abstract

The circuit interfaces dialing signal between a data terminal and a dial-up modem in a digital communication system using a data mod- demodulator. The circuit includes 1st, 2nd RS-232C connectors (10,12) connected to a data terminal equipment (DTE) and a data circuit terminating equipment (DTE) of a dial-up modem respectively, a data mod-demodulator (14) for generating mod-demodulated input data and control signal for signal switching, 1st and 2nd multiplexers (22,24), a line driver (26) for converting the signal of TTL level to the signal of transmitting level, and a controller (28).

Description

Dial Signal Interface Circuit for Data Modulator and Dial-Up Modem

1 is a dial signal interface circuit according to the present invention.

2 is a partial operation waveform diagram of FIG.

* Explanation of symbols for main parts of the drawings

10,12: 1st, 2RS-232C 14: Data Modulator

16,20: line receiver 18,26: line driver

22,24: first and second multiplexer 28: control circuit

The present invention relates to a modem interface circuit, and more particularly, to a dial-up modem that does not modulate a dialing signal for a call connection when using a digital data modem in a digital communication network using a dial-up modem. It relates to a dial signal interface circuit.

Typically, dial-up modem refers to a modem connected to a dial-up line, which is a public switching line, and means dialing and telephone. The dial-up modem as described above receives a dial signal of a data terminal equipment (DTE) and dials a switching line to perform a call connection with a communication partner modem.

At present, such dial-up modems are commonly used by connecting DTE and RS-232C cables. However, when using a data modulator to secure data output from a DTE in a data communication network using the dial-up modem as the data circuit-terminating equipment (DCE), an interface of a dial signal has been a problem. That is, in the system for first digitally demodulating the output data of the DTE with a data demodulator to secure the data output from the DTE in a data communication network, all data output from the DTE in the system for secondary modulation and demodulation of the modulated data with a dial-up modem. Must not be altered or demodulated. This is because the data initially output from the DTE of the system using the dial-up modem as DCE is also dial signal data for calling the modem of the other party. When this is modulated and output through the data demodulation device, the call connection with the other party is impossible. to be.

Therefore, even when DCE is a dial-up modem when using a data demodulator for data security function in a digital data communication network, it is a dial signal necessary for call connection with a communication counterpart so that it is not modulated by the data demodulator and the data is actually transmitted and received. After primary modulation and demodulation through the dial-up modem connected to the switched line, secondary modulation and demodulation shall be performed. Therefore, even when a data modulator is used in a digital communication network, a dial signal interface for DCE-interfaceting only the dialing signal for the call connection output from the DTE is required.

Accordingly, an object of the present invention is to provide a circuit for interfacing a dialing signal between a data terminal and a dial-up modem in a digital communication system using a data modulator.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a circuit diagram according to the present invention, wherein the first and second RS-232C connectors (hereinafter referred to as RS-232C) 10 and 12 are connected to the data terminal DTE and DCE of the dial-up modem by RS-232C, respectively. Connected between the first and second RS-232Cs (10, 12) through a line receiver (10) and a line driver (18) to provide an RTS output from a DTE as an RTS signal of a DCE, and output / modulated / demodulated data And a data modulator 14 for outputting a signal switching control signal, a CTS (M) and a DCD (M) terminal of the second RS-232C (12) and a TXD (T) of the first RS-232C (10). A line receiver 20 connected to a terminal and an RXD (M) terminal of the second RS-232C (12) and receiving a signal of a transmission level output from each terminal inverted into a TTL level signal, and a control signal input terminal. It is connected between the output terminal of the line receiver 20 and the input terminal of the data modulator 14, and is input to the control signal input terminal A first multiplexer 22 (hereinafter referred to as “MUX1”) 22 which is switched by a transmission / reception control signal and provides an output of the line receiver 20 to the data modulator 14, and the data modulator 14 First and second input ports 1A-4A and 1B-4B are connected to an output terminal and an output terminal of the line receiver 20. The first and second input ports 1A-4A and 1B-4B are connected to each other. A second multiplexer 24 for selecting and outputting one of the second input ports 1A-4A and 1B-4B; and an output terminal of the MUX2 24 and the first RS. TTL level is connected to the CTS (T) and DCD (T) terminals of the 232C (10), the TXD (M) terminal of the second RS-233C (12) and the RXD (T) terminal of the first RS-232C (10). A data carrier test is connected to a line driver 26 which converts a signal into a signal of a transmission level, a DCD (M) output port of the line receiver 20 and a signal switching control signal output port of the data modulator 14; It is composed of a control circuit 28 which provides transmission and reception control signals to the control signal input terminals of the MUX1 22 and the MUX2 24 when the origin code is input.

2 is an operational waveform diagram of a portion of FIG. In this case, RTS is Request to send, CTS is Clear to send, DCD is Data Carrier Detect, and RXD is Received Data. , TXD is transmit data, T in parentheses indicates that the signal on the terminal side, M is a signal of DCE which is a dial-up modem (not shown). The unmarked DSR is a data set ready signal indicating whether the dial-up modem is powered on or off. The above abbreviations are known to those of ordinary skill in the art, and thus, the detailed description of the terms is as follows. Is omitted. The user now has data communication with the other party via a dial-up modem (not shown but connected to the second RS-232C 12) connected to the telephone network, and a hook-off message to the DTE connected to the first RS-232C 10. If D is inputted, the DTE outputs an RTS signal to the RTS (T) of the first RS-232C 10. At this time, the data modulator 14 inputting the RTS (T) signal outputs, through the line driver 18, the RTS (M) signal, which is a transmission request signal as shown in FIG. 2a, to DCE, which is a dial-up modem. The dial-up modem having inputted the transmission request signal RTS (M) through the second RS-232C 12 transmits a transmission permission signal CTS (M) as shown in FIG. 2B in response to the transmission request signal RTS (M). 20). The line receiver 20 which inputs the transmission permission signal CTS (M) converts the signal to a TTL level and outputs them to the input terminals 1A and 1B of the MUX1 22 and the MUX2 24, respectively.

MUX1 (22) and MUX2 (24) for inputting the transmission permission number CTS (M) to terminals (1A) and (1B), respectively, are inputted by a transmission / reception control signal inputted initially as "high" to the selection terminal (S). The signals input to the ports 1B-4B are selectively output. At this time, the control circuit 28 executes the control of the MUX1 and MUX2 22 and 24. The control circuit 28 transmits and receives the control signal MUX1 according to the carrier detection signal TCM inverted through the line receiver 20. The control signal of MUX2 (22, 24) is output.

That is, the signal is provided by the enable signal inputted to the other end of the AND gate 34 for inputting the signal switching control signal CTL output from the initial data modulator 14 to the high terminal as shown in FIG. 2f. The switching control signal CTL is gated to output a transmission / reception control signal to the selection terminals S of the MUX1 22 and the MUX2 24. At this time, the output of the oragate 32 which logically sums the output of the line receiver 20 which inverts the data carrier detection signal DCD (M) of the dial-up modem to the TTL level on the other side of the AND gate 34. The dial-up modem outputs the data carrier detect signal DCD (M) as low until the call is connected to the other party.

Therefore, by inputting the data carrier detect signal DCD (M) inverted as shown in FIG. 2g in the oragate 32 line receiver 20 to the other side of the AND gate 34, the initial "high" signal to the AND gate 34. Are input to the selection terminals S of MUX1 (22) and MUX2 (24). Accordingly, the MUX1 22 selects the signal “high” through the resistor R1 and outputs it to the data modulator 14, and the MUX2 24 outputs the transmission permission signal CTS (M) inverted by the line receiver 20. Select and output to the output terminal 1Y. Therefore, the transmission permission signal CTS (M) output from the dial-up modem is input to the DTE via the line driver 26 and the first RS-232C 10. The DTE which inputs the transmission permission signal CTS (M) will display it as usual. Thereafter, when the user inputs a dial (phone number) of the other party's modem to communicate using the keyboard of the DTE, the dial signal from the DTE is output. At this time, the data is input to the line receiver 20 as shown in FIG. 2I through the TXD (T) terminal of the first RS-232C 10. After receiving the dial data outputted from the RS-232C 10 as shown in FIG. 2I, the line receiver 20 converts it to a TTL level and then inputs the respective input terminals 3A of the MUX1 22 and the MUX2 24. Enter (3B).

At this time, the MUX1, MUX2 (22, 24) is the first of the two first, second input ports (1A-4A) (1B-4B) by the "low" transmission and reception control signal initially input to the selection terminal (S) The signal of one input port 1B-4B is selectively outputted. Accordingly, the MUX1 22 outputs a signal through the resistor R1 to the data modulator 14, and the MUX2 24 selects and outputs a dial data signal of 2I as shown in FIG. 2C through the line receiver 20. Output to terminal 3Y. The signal output from the output terminal 3Y of the MUX2 24 is input to the transmission data TXD (M) of the second RS-232C 12 connected to the dial-up modem via the line driver 26. Therefore, the dial data outputted from the DTB as shown in FIG. 2C is input to the dial-up modem without being modulated by the data modulator 14.

That is, the dial signal of TXD (T) of the DTE is directly input to the dial-up modem through MUX2 24 without passing through the data modulator 14. At this time, the dial-up modem dials the other modem by dial data input through the RS-232C 12 and checks whether the carrier is received like a normal modem.

When a call of the opposite modem is connected and a carrier of the data transmitted from the opposite party is detected, the dial-up modem transmits the data carrier direct signal DCD of the transmission level logic “high” to the DCD (M) as shown in FIG. Output (M)

After receiving the data carrier detection signal DCD (M), the line receiver 20 converts the signal into a TTL level signal and inverts the signal of FIG. 2e as shown in FIG. 2g to output to the oragate 32. The OA gate 32 inputs the data carrier detect signal DCD (M) input to "low" to the other end of the AND gate 34 (in this case, the DSR (M) dials the signal output from the dial-up modem). -The signal is input to logic “high” when power is supplied to the up-modem, which causes the inverter 30 to output low, according to the data carrier decode DCD (M). .

By the output "low" of the oragate 32, the AND gate 34 outputs a transmission and reception control signal of a logic "low" as shown in FIG. 2h to the select terminals S of the MUX1 and MUX2 22 and 24. Each of the MUX1 and MUX2 22 and 24 is connected to the first input port 1A- of the two first and second input terminals 1A-4A and 1B-4B by the output “low” of the AND gate 34. Only 4A) will be selected. Therefore, the MUX1 22 selects the output of the line receiver 20 and inputs it to the data demodulator 14, and the MUX2 24 selects the output of the data modulator 14 through the line driver 26. The second RS-232C 12 connected to the dial-up modem is input.

After the call is connected as described above, when communication data such as (2J) of FIG. 2C is outputted from the DTE, the data modulator through the input terminal 3A and the output terminal 3Y of the line receiver 20 and the MUX1 22. The transmission data of (14) is input to an input terminal. At this time, the data modulator 14 modulates a data input such as (2J) of FIG. 2c as shown in (2L) of FIG. 2d, and outputs it to the input terminal 3A of the MUX2 24. Modulation data as shown in Fig. 2L is selected and output to the second RS-232C 12 connected to the dial-up modem via the line driver 26. Therefore, after the call connection is completed, communication is performed after the first modulation is performed by the data modulator 14 to the data to be actually communicated.

As described above, the present invention can transmit a dial signal to a dial-up modem independently when using a data modulator to secure data transmitted and received on a line in a digital communication network, thereby easily implementing a modem system with a security function.

Claims (1)

A dial signal interface circuit of a data modulation / demodulator and a dial-up modem, comprising: first and second RS-232C connectors (10, 12) connected to a data terminal (DTE) and a DCE of a dial-up modem by RS-232C, respectively; The RTS output from the DTE is connected to the line receiver 16 and the line driver 18 between the first RS-232C connectors 10 and 12 as the RTS signal of the DCE, and the input / output data is modulated and output. A data modulator 14 for outputting a signal switching control signal, the CTS (M) and DCD (M) terminals of the second RS-231C connector 12 and the TXD (T) of the first RS-232C connector 10. A line receiver 20 connected to the terminal and the RXD (M) terminal of the second RS-232C connector 12 for inverting and receiving the transmission level signal outputted from the respective terminals into a TTL level signal, and a control signal input terminal. Between the output terminal of the line receiver 20 and the input terminal of the data modulator 14 A first multiplexer 22 which is switched by a transmission / reception control signal input to the control signal input terminal and provides an output of the line receiver 20 to the data demodulator 14, and the data demodulator ( The first and second input ports 1A-4A (1B-4B) are connected to the output terminal 14 and the output terminal of the line receiver 20, and are controlled by the transmission / reception control signal input to the control signal input terminal. A second multiplexer 24 for selectively outputting one of the first and second input ports 1A-4A and 1B-4B, an output terminal of the second multiplexer 24, and the first RS-232C; TTL level by being connected to CTS (T), DCD (T) terminals of connector 10, TXD (M) terminal of second RS-232C connector 12 and RXD (T) terminal of first RS-232C connector 10 Signal conversion agent of the line driver 26 for converting a signal of the signal into a transmission level signal, the DCD (M) output port of the line receiver 20, and the data modulator 14; And a control circuit 28 connected to a signal output port and configured to provide transmission and reception control signals to the control signal input terminals of the first and second multiplexers 22 and 24 upon input of the data carrier detection signal. Dial signal interface circuit of dial-up modem.

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