JPH0856241A - Modem device - Google Patents

Abstract

PURPOSE:To provide a modem device capable of communicating with diversified communication opposite parties with a simple operation. CONSTITUTION:Frequency pattern detection means 12 to 14 detect the presence pattern of a frequency component in a modulation signal received from a communication line 4 and a MODEM system election means 15 selects any MODEM section in MODEM means 1 depecding on the pattern of the detected frequency component. Thus, the same modulation demodulation system as that of a MO DEM device of the communication opposite party is set to the MODEM device 10. Moreover, different communication protocol is precessed in this method in addition to the selection of the modulation demodulation system depending on a communication purpose (communication opposite party) by allowing a communication protocol changeover means to select the communication protocol based on the pattern of the frequency component detected by the frequency pattern detection means 12 to 14 and the data demodulated by the MODEM means 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modem device, and can be applied to, for example, a communication system for performing data communication with a host computer or the like using a telephone network, a dedicated line or the like.

[0002]

2. Description of the Related Art When data communication is performed between two points using a telephone network or a dedicated line, a modem device is provided on the line side of a data processing device at each point, and the communication data is modulated by this modem device. The signal is converted into a signal and sent out on the line, and the modulated signal transmitted on the line is demodulated into communication data to be input to the data processing device. In many communication systems, one of the data processing devices that executes data communication via such a modem device is a host computer.

A conventional modem device 1 for converting between communication data and modulated signals as described above, as shown in FIG.
CPU (ce of data processing device (host computer etc.)
A CPU bus interface 3 is connected to an ntral processing unit (bus) 2, and a network monitoring control unit (NCU) 5 is connected to a communication line 4 such as a telephone network or a leased line. The CPU bus interface 3 is formed of a buffer circuit or the like, inputs and outputs address data and communication data used for transmission between the CPU bus 2 and the transmission / reception control unit 6, and further, the CPU bus 2 and the network monitoring control unit 5. Connect between them with a control line. As a result, in the modem device 1, C
A data processing device is formed so as to control the network monitoring control unit 5 and the transmission / reception control unit 6 via the PU bus interface 3, and is also adapted to input / output communication data to / from the transmission / reception control unit 6. . The network monitoring control unit 5 monitors the state of the communication line 4 and executes connection control for incoming and outgoing calls. That is, the network monitoring control unit 5 uses the communication line 4
When an incoming signal (CI signal: calling indicator) is input from the device, a predetermined line connection process is executed in response to the CI signal, and a reception connection request is sent to the data processing device via the CPU bus interface 3. . Conversely, C
When communication is started from the data processing device via the PU bus interface 3, the network monitoring control unit 5 sends an outgoing signal to the communication line 4 to execute line connection processing, and when the line is connected, the CPU The data processing device is notified via the bus interface 3.

The transmission / reception control unit 6 inputs / outputs data used for data communication between the CPU bus interface 3 and the modem unit (modulation / demodulation unit) 7. At this time, the transmission / reception control unit 6
Is set with a communication protocol such as a synchronous / asynchronous method or an error control method via the CPU bus interface 3.
Data is input to and output from the modem unit 7 according to this communication protocol. The modem unit 7 converts the parallel data output from the transmission / reception control unit 6 into serial data, further modulates the data according to a predetermined modulation / demodulation method, and outputs the modulated data to the network monitoring control unit 5, and also according to this modulation / demodulation method, the network monitoring control unit. 5
The modulated signal input via the is demodulated into parallel data (communication data) and output.

As described above, in the modem device 1, the CPU
When a communication program is started by the data processing device connected to the bus 2, the network monitoring control unit 5 and the transmission / reception control unit 6 are executed by this central processing unit via the CPU bus interface 3.
Is controlled and a line is connected to the communication target, and then the data inputted from the CPU bus 2 is modulated by the modem section 7 and transmitted. On the other hand, when an incoming signal is input from the communication target, after the line is connected in response to the incoming signal, the control data and the like transmitted subsequently are demodulated by the modem unit 7 and converted into parallel data. Output to the CPU bus 2.

[0006]

When performing data communication as described above, in the modem device 1, the modulation / demodulation method of the built-in modem unit 7 may match the modulation / demodulation method of the communication object. You will need it. Further, the communication protocol of the modem device 1 needs to match the communication protocol of the communication target.

Therefore, in the data communication using the conventional modem device, the modem device is replaced according to the modulation / demodulation method of the communication target, the usable modem device is restricted, and the communication protocol of the communication target is matched. As described above, it is necessary to selectively start the application program, which is a communication program, and eventually the user needs to perform complicated work.

If the exchange work and the selection work can be simplified, the usability of this type of data communication system can be further improved, and it is considered to be convenient.

For example, when a common host computer communicates with many data terminals, there are a plurality of types of data terminals, and when the data terminals of different types have different modulation and demodulation methods, the host computer has different types of data terminals. A modem device must be provided, the system scale becomes large, and a modem device for one type of data terminal is not used for communication with another type of data terminal, resulting in poor operation rate.

[0010]

In order to solve such a problem, according to the present invention, a modem which modulates communication data, sends the modulated signal to a communication line, and demodulates a modulated signal from the communication line into communication data. The equipment was as follows.

That is, the modulation / demodulation means having a plurality of modulation / demodulation sections for performing modulation / demodulation according to different modulation / demodulation methods, the frequency pattern detection means for detecting the frequency component of the modulated signal input from the communication line, and the pattern of the detected frequency component. In accordance with the above, a modulation / demodulation system selection means for selecting any one of the modulation / demodulation units in the modulation / demodulation means is provided.

Further, communication protocol switching means for switching the communication protocol may be provided in accordance with the pattern of the frequency component detected by the frequency detecting means and the data demodulated by the modulating / demodulating means.

[0013]

According to the present invention, the frequency pattern detecting means detects the frequency component contained in the modulated signal inputted from the communication line, and the modulation / demodulation system selecting means selects one of the modulation / demodulation means according to the detected frequency component pattern. Select the modem unit. As a result, the modem device can be set to the same modulation / demodulation system as that of the modem device of the communication partner.

Further, if the communication protocol switching means switches the communication protocol in accordance with the pattern of the frequency component detected by the frequency detecting means and the data demodulated by the modulating / demodulating means, the modulation / demodulation according to the communication purpose (communication partner). Not only the system but also the communication protocol can be changed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment in which a modem device of the present invention is applied to a computer network system will be described below in detail with reference to the drawings. Here, FIG. 1 shows the detailed configuration of the first embodiment, and the same parts as those in FIG. 2 described above are designated by the same reference numerals.

Referring to FIG. 1, the modem device 1 of this embodiment.
Reference numeral 0 has a modem unit (modulation / demodulation means) 11 adapted to switch the modulation / demodulation system according to the modem selection signal SEL. That is, although not shown in detail, the modem section 11 has a plurality of modulation / demodulation configurations for performing modulation / demodulation according to different modulation / demodulation schemes, and selectively uses the modulation / demodulation configurations according to the modem selection signal SEL. As a result, the modem device 1
In 0, the modulation / demodulation method corresponding to the communication target can be selected. For example, as a plurality of modulation / demodulation methods, an FSK method, a PSK method, etc. can be mentioned.

The modem device 10 outputs the modulated signal coming from the communication partner via the communication line 4 from the network monitoring control part 5 to the modem part 11 and at the same time the frequency pattern detecting circuit 1
Output to 2.

The frequency pattern detection circuit 12 has a plurality of frequency component discriminators 12A to 12X, which are formed by connecting the input sides of these frequency component discriminators 12A to 12X in parallel. For example, each of the frequency component determination units 12A to 12X is formed of a bandpass filter having a different center frequency and a detection circuit that detects the output signal of each bandpass filter. The center frequency of each bandpass filter is selected so as to correspond to the modulation / demodulation method switched by the modem unit 11. For example, in consideration of a certain FSK method, the center frequencies of at least two band pass filters are selected as the frequency when the logic "1" and the frequency when the logic "0" in the FSK method.

As a result, the modem device 10 can detect the output signal levels of the frequency component discriminating units 12A to 12X, detect the frequency pattern of the incoming modulated signal, and specify the modulation / demodulation method of the communication partner. Has been done.

The frequency pattern detection circuit 12 outputs the output signals of the respective frequency component discriminating sections 12A to 12X to the flip-flop circuits 13A to 13X, respectively, and the flip-flop circuits 13A to 13X are cleared by the clear signal CR, The output signals of the frequency component discriminating units 12A to 12X are fetched by the timing clock CK, and the output signal levels of the frequency component discriminating units 12A to 12X are detected by this. The clear signal CR and the timing clock CK
May be generated sequentially when the network monitoring control unit 5 detects an incoming call, or may be sequentially generated when the transmission / reception control unit 6 receives an incoming signal from the network monitoring control unit 5.

The frequency pattern detection register 14 takes in and holds the output signals of the flip-flop circuits 13A to 13X at a predetermined timing, whereby the modem device 1
At 0, the detection result of the frequency pattern detection circuit 12 is held in the frequency pattern detection register 14. The frequency pattern held in the frequency pattern detection register 14 is given to the CPU bus interface 3 and the selection circuit 15.

The upper central processing unit 16 connected to the CPU bus 2 can detect the contents held in the frequency pattern detection register 14 via the CPU bus interface 3, and detect the modulation / demodulation method of the communication object from the detection result. It is designed to get you. The upper central processing unit 16 is
As will be described later, the type of the detected modulation / demodulation method also determines the communication protocol to be used as one condition, and also determines the communication program (application program) to be used.

The selection circuit 15 decodes the frequency pattern held in the frequency pattern detection register 14 to generate a modem selection signal SEL, and outputs the modem selection signal SEL to the modem section 11. Thereby, the modulation / demodulation system of the modem unit 11 is switched so as to correspond to the modulation / demodulation system of the communication partner.

When the line connection request is input through the communication line 4, the modem unit 11 not only switches the modulation / demodulation method to correspond to the communication partner, but also the CPU
When a line connection request is input from the upper central processing unit 16 connected to the bus 2, the modulation / demodulation system is switched according to the instruction of the upper central processing unit 16.

The upper central processing unit 16 sends demodulated data obtained by the modem section 11 demodulating the modulated signal coming from the communication partner following the connection request, and the transmission / reception control section 6 and the CP.
Captured via the U-bus interface 3. The upper central processing unit 16 detects the communication protocol of the communication partner based on the modulation / demodulation method of the communication partner and the demodulated data. The upper central processing unit 16 selectively activates a plurality of communication programs prepared in advance based on the detection result of the communication protocol and the modulation / demodulation method, and outputs a control command to the transmission / reception control unit 6 according to the communication programs. , Execute the communication procedure.

In the above configuration, the modem device 10 is
It waits for a line connection request from the CPU bus 2 or the communication line 4, and when the line connection request arrives, the corresponding process is executed.

That is, as shown in FIG. 3, in the modem device 10, when the power is turned on, step SP1
To SP2, it is determined whether or not a line connection request is input from the higher-level central processing unit 16 connected to the CPU bus 2. If a negative result is obtained here, the process proceeds to step SP3. Here, the modem device 10 determines whether or not a line connection request (CI signal) is detected by the network monitoring control unit 5, and if a negative result is obtained, the process returns to step SP2.

As a result, the modem device 10 operates in step S.
When the line connection request is input from the upper central processing unit 16 by repeating the processing procedure of P2-SP3-SP2, a positive result is obtained in step SP2, and step SP2
Go to 4.

Here, the modem device 10 includes the network monitoring control unit 5
Then, the line connection process is started, and in the next step SP5, the network supervisory control unit 5 sends an outgoing signal.

Subsequently, in the modem device 10, the process proceeds to step SP6, and the modulation / demodulation method of the modem unit 11 is set according to the control command input via the CPU bus interface 3. That is, the modulation / demodulation method is set by the upper central processing unit 16 in correspondence with the communication partner who has transmitted the transmission signal.

The modem device 10 subsequently sets a communication protocol such as a synchronous / asynchronous system or an error control system in the transmission / reception control unit 6 in accordance with a control command input via the CPU bus interface 3. That is, the communication protocol is set by the higher-level central processing unit 16 corresponding to the communication partner who has transmitted the transmission signal.

In the following step SP7, the modem device 10 selects the communication programs A to X in accordance with the set communication protocol and modulation / demodulation method, and in steps SP8A to
In SP8X, data communication is performed according to the communication programs A to X.

When the communication end command is input from the upper central processing unit 16, the modem device 10 moves to the next step SP9, where the transmission / reception control unit 6 and the network monitoring control unit 5 execute the communication end process. After that, step SP2
Return to and wait for the subsequent data communication.

As described above, in modem device 10, data communication can be performed as the originating side by switching the modulation / demodulation method to correspond to the communication target without having to replace the modem device one by one.

On the other hand, when an incoming signal is input through the communication line 4, the modem device 10 obtains a positive result in step SP3, and thus the process proceeds to step SP10 and the upper central processing unit 16 is reached. At the same time as notifying the line connection request, the network monitoring control unit 5 executes the line connection process.

The modem device 10 then proceeds to step SP1.
1, the frequency pattern detection circuit 12 detects the presence pattern of the frequency component of the modulated signal that follows the incoming signal, and flip-flop circuits 13A to
The detection result is held in the register 14 via 13X. The upper central processing unit 16 fetches the contents of this register 14 via the CPU bus interface 3.

Then, the modem device 10 performs step SP1.
2, the selection signal SEL is output from the selection circuit 15 to set the modulation / demodulation method of the modem unit 11, whereby the modulation / demodulation method is switched to correspond to the communication partner.

Further, the modem device 10 outputs the demodulated data output from the modem section 11 to the bus 2, and the upper central processing unit 16 determines the detected modulation / demodulation method of the communication object and the communication protocol based on the demodulated data. Then, the corresponding communication program is selected and activated based on this determination result. As a result, the modem device 10 becomes
A synchronous / asynchronous method, an error control method or the like is set in the transmission / reception control unit 6 according to a control command input via the bus interface 3. In subsequent step SP7, the modem device 10 branches to the selected communication programs A to X, and executes data communication in accordance with the communication programs A to X in steps SP8A to SP8X.

As described above, in the modem device 10, even if the modem device is not exchanged and the communication program corresponding to the communication object is not selected and activated by the user, the communication device can correspond to the communication object. The data communication can be executed as the receiving side by switching the modulation / demodulation method and the communication protocol.

According to the first embodiment, by detecting the existence pattern of the frequency component of the modulated signal and switching the modulation / demodulation system based on the detection result, data communication can be performed without exchanging the modem device one by one. Thus, data communication can be performed with a simple operation.

Further, according to the first embodiment, by switching the communication protocol based on the detected modulation / demodulation method and the demodulation result, it is possible to omit the complicated operation of selecting and starting the communication program, and the data can be easily operated by that much. Can communicate.

Next, a second embodiment in which the modem device of the present invention is applied to a computer network system will be described in detail with reference to the drawings. Here, FIG. 4 shows this second
The detailed configuration of the embodiment is shown, and the portions corresponding to those in FIG. 1 described above are denoted by the same reference numerals.

Referring to FIG. 4, the modem device 2 of the second embodiment.
In 0, a central processing unit (CPU) 22 and a read only memory (ROM) 21 are arranged in place of the selection circuit 15 (FIG. 1) of the first embodiment.

The central processing unit 22 is a local CPU that executes the firmware program stored in the read-only memory 21 and controls the operation of the entire modem device 20. The central processing unit 22 monitors and controls the state of the network monitoring control unit 5, and sends a line connection request or the like to the upper central processing unit 23 via the bus 2 as necessary.
Further, the central processing unit 22 outputs a selection signal SEL to the modem section 11 in response to the application program of the upper central processing unit 23 and based on the detection result of the register 14, whereby the modem section 11 performs modulation / demodulation. Switch the method.

The central processing unit 22 includes a transmission / reception control unit 6
A communication protocol is set based on the demodulated data output from the upper central processing unit 23 and in response to the application program of the upper central processing unit 23, and subsequently, the data input / output to / from the upper central processing unit 23 is set as necessary. Convert data.

As a result, even if the communication protocol corresponding to the communication target is not prepared in the upper central processing unit 23, in other words, for example, the haze AT command, C
CITT V. If a fixed protocol such as the 25bis command is prepared and the upper central processing unit 23 executes the fixed communication protocol, the central processing unit 22 of the modem device 20 selectively sets the communication protocol as necessary.
That is, the load on the upper central processing unit 23 can be significantly reduced.

Therefore, the firmware program stored in the read-only memory 21 is formed so that this type of series of processing can be executed by the central processing unit 22, and further, a plurality of communication protocols corresponding to the communication target are formed. It is designed so that you can select and execute.

In the above configuration, the central processing unit 22 of the modem device 20 waits for a line connection request from the CPU bus 2 or the communication line 4 and executes the corresponding process when the line connection request arrives.

That is, in FIG. 5 and FIG. 6, the central processing unit 22 of the modem device 20 has the step SP21.
Moves from step SP22 to upper central processing unit 2
It is determined whether or not a line connection request is input from 3, and if a negative result is obtained here, the process proceeds to step SP23, and the network monitoring control unit 5 determines whether or not a line connection request is detected.
When a negative result is obtained, the process returns to step SP22.

As a result, the central processing unit 22 repeats the processing procedure of steps SP22-SP23-SP22 and holds the modem device 20 in the standby state.

At this time, the higher-level central processing unit 23 moves from step SP24 to step SP25 to judge whether the user has performed an operation for making a call. If a negative result is obtained here, the higher central processing unit 23 moves to step SP26 and the modem device. 20
It is determined whether or not the line connection request is notified from, and if a negative result is obtained, the process returns to step SP24.

As a result, the upper central processing unit 23
The processing procedure of steps SP24-SP25-SP24 is repeated, and the data communication application program executed by the upper central processing unit 23 is held in the standby state.

On the other hand, when the user executes a data communication operation, the upper central processing unit 23 makes a step S
When a positive result is obtained in P25, the process proceeds to step SP27, and the data communication application program is activated. As a result, the upper central processing unit 2
3 issues a call-out command to the modem device 20 according to the fixed protocol of this application program, and then issues a control command in the following step SP28 to control the protocol of the modem device 20, and in step SP2.
9 and waits for a response from the modem device 20.

On the other hand, when the central processing unit 22 of the modem device 20 receives the call-out command from the upper central processing unit 23, an affirmative result is obtained in step SP22, and the process proceeds to step SP30. Here, the central processing unit 22 activates the firmware program stored in the read-only memory 21, activates the network monitoring controller 5 in accordance with this firmware program, and starts the line connection processing.

Further, the central processing unit 22 subsequently sends an outgoing signal from the network supervisory control unit 5 in step SP31 in accordance with the control command output from the upper central processing unit 23, and then sends the outgoing signal in step SP32. The modulation / demodulation method of the modem unit 11 is set according to the communication partner, and the corresponding communication protocol is set in the transmission / reception control unit 6.

As a result, when the central processing unit 22 becomes ready to start data communication, it sends a setting completion response to the upper central processing unit 23, and the upper central processing unit 23 receives this response and proceeds to step SP33. It is judged whether or not it is possible to move and communicate. Central processing unit 2
For example, in the case where the communication target is in a call and the line cannot be connected, for example, 2 issues a notification that the call is difficult instead of the response of the completion of the setting, and the upper central processing unit 23
When such a notification is received, a negative result is obtained in step SP33, and the process proceeds to step SP34.

The upper central processing unit 23 displays an error message on the display screen to notify the user that it is difficult to perform data communication, and then proceeds to step SP35 to issue a communication end command to the modem device 20, It returns to step SP25.

In response to this, the central processing unit 22 of the modem device 20 controls the network monitoring controller 5 in step SP36 to cut off the line, and then returns to step SP22.

On the other hand, when the central processing unit 22 sends a response indicating that the data communication can be started, the upper central processing unit 23 obtains a positive result in step SP33, and moves to step SP37.
Data is transmitted by accessing a file or the like selected by the user. In response to this, the central processing unit 22 of the modem device 20 performs branch processing at step SP38, then performs data conversion of the data sequentially input according to the communication program selected at steps SP39A to 39X, and also the transmission / reception control unit 6 Send through.

When the data is transmitted in this manner, the upper central processing unit 23 moves to step SP40, judges whether the communication is completed or not, and a negative result is obtained when the data for data communication still remains. When obtained, the process returns to step SP37.

As described above, in the modem device 20, even if the communication program is not selectively activated on the upper central processing unit 23 side, successively continuous data is sent to the communication partner according to the communication protocol corresponding to the communication partner. be able to.

On the other hand, when a communication end command is input from the communication partner, or when the user executes a call end operation, etc., the upper central processing unit 23
When a positive result is obtained in step SP40, the process proceeds to step SP35, and a call end command is issued.

In response to this, the central processing unit 22 of the modem device 20 moves from step SP39A to 39X to step SP36, controls the network monitoring control unit 5 to disconnect the line, and then returns to step SP22.

On the other hand, when the incoming signal is input through the communication line 4 in the standby state, the central processing unit 22 obtains a positive result in step SP23, and proceeds to step SP41. At this time, the central processing unit 22 notifies the upper central processing unit 23 of the line connection request, whereby the upper central processing unit 2 is notified.
In 3 as well, a positive result is obtained in step SP26, and the routine goes to step SP42.

Here, the upper central processing unit 23 issues a line connection command to the modem device 20 in accordance with the fixed protocol, then moves to step SP29, and the modem device 20.
Wait for a response from. In response to this line connection command, the central processing unit 22 of the modem device 20 makes a step S
In P41, after controlling the network monitoring control unit 5 to connect the line, the process proceeds to step SP43, the contents of the register 14 are detected, and the existence pattern of the frequency component of the modulation signal is detected.

The central processing unit 22 then proceeds to step SP44, judges the modulation / demodulation method of the communication partner based on the detection result of the register 14, and then outputs the selection signal SEL based on this judgment result, thereby communicating. The modem unit 11 is set to the modulation / demodulation method corresponding to the partner. further,
The central processing unit 22 subsequently monitors the output data of the transmission / reception control unit 6, determines the communication protocol based on the modulation / demodulation method and this output data, and sends a control command to the transmission / reception control unit 6 based on this determination result. Issue.
As a result, the central processing unit 22 sets the communication protocol so as to correspond to the communication partner even when the upper central processing unit 23 holds only the fixed protocol, and after performing the data communication according to the set communication protocol. , Go to step SP36.

According to the second embodiment described above, by switching the communication protocol on the modem device side in correspondence with the communication partner, it is possible to prepare a communication program corresponding to the communication partner on the side of the upper central processing unit. A fixed protocol can be executed and the communication protocol of the modem device 20 can be selected and set as needed, which can significantly reduce the load on the upper central processing unit in addition to the effects of the first embodiment. Has the effect.

In the above embodiment, the flip-flop circuit is used to hold the detection result of the frequency pattern detection circuit, but the frequency pattern holding structure is not limited to this.

Further, in the above embodiment, the case where the existence pattern of the frequency component is detected by using a plurality of band pass filters has been described, but the present invention is not limited to this, and a frequency detecting means such as a counter may be used. It may be used, or fast Fourier transform or the like may be used.

[0070]

As described above, according to the present invention, a modulation / demodulation means having a plurality of modulation / demodulation units for performing modulation / demodulation according to different modulation / demodulation systems, and a frequency pattern for detecting a frequency component contained in a modulation signal input from a communication line. Since the detection means and the modulation / demodulation method selection means for selecting one of the modulation / demodulation units in the modulation / demodulation means according to the detected frequency component pattern are provided, the modem device is replaced one by one or the application program is selectively activated. Even if it is not necessary, it is possible to set the modulation / demodulation method (and communication protocol) corresponding to the communication partner, and thereby data communication can be performed by a simple operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing a modem device according to a first embodiment.

FIG. 2 is a block diagram showing a conventional modem device.

FIG. 3 is an operation flowchart of the first embodiment.

FIG. 4 is a block diagram showing a modem device according to a second embodiment.

FIG. 5 is an operation flowchart of the modem device according to the second embodiment.

FIG. 6 is an operation flowchart of a higher-level central processing unit according to the second embodiment.

[Explanation of symbols]

10, 20 ... Modem device, 3 ... CPU bus interface, 4 ... Communication line, 5 ... Network monitoring control unit (NC
U), 6 ... Transmission / reception control unit, 11 ... Modem unit, 12 ...
... Frequency pattern detection circuit, 12A to 12X ... Frequency component discrimination unit, 13A to 13X ... Flip-flop circuit, 14 ... Frequency pattern detection register, 15 ... Selection circuit, 16, 22, 23 ... Central processing unit.

Claims (2)

[Claims] 1. A modem device for modulating communication data, transmitting a modulation signal to a communication line, and demodulating a modulation signal from the communication line into communication data, comprising a plurality of modulation / demodulation units for performing modulation / demodulation according to different modulation / demodulation methods. The modulation / demodulation means included therein, the frequency pattern detection means for detecting the frequency component included in the modulated signal input from the communication line, and one of the modulation / demodulation units in the modulation / demodulation means is selected according to the pattern of the detected frequency component. A modem device characterized by comprising a modulation / demodulation system selecting means for selecting the modem device. 2. A communication protocol switching means for switching the communication protocol according to the pattern of the frequency component detected by the frequency detecting means and the data demodulated by the modulating / demodulating means.
Modem device described in.