JPH10136113A - Modem - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the state of a reception modem from being transited into a demodulation state of control channel data in mistake by conducting sequence control based on non-detection/detection of a partial page control restoration frame in the ECM mode during reception of primary channel data. SOLUTION: A state 100 indicates a primary channel data(PCD) demodulation state of a reception modem and a state 101 depicts a control channel data demodulation state of the reception modem. The reception modem stays in the state 100 while not detecting (1-1) a partial page restoration control frame(RCP) during the reception of the PCD. The PCD in the ECM mode are made up of a synchronizing signal, facsimile coded data(FCD) and the RCP frame, and when any RCP frame is detected, it is regarded as the end of the FCD, the reception modem is transited to the state 101 through the detection (1-2) of the RCP. Thus, even on the occurrence of a line fault such as momentary interruption, the state transition from the state 100 into the state 101 is conducted without an error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modem device for performing data transmission using a communication line, and more particularly to a modem device having a sequence control for changing an operation according to each state of the device.

[0002]

2. Description of the Related Art Generally, when digital signal data is transmitted via a general public line (analog line), a modem (modem) device for converting a digital signal into a desired analog signal and performing the reverse conversion is required. Become.

[0003] Among modem devices, in particular,
ITU-T V-Series Recommendation V.4 with transmission speeds from 2.4 kbps to 33.6 kbps 34 has been recommended as a full-duplex / half-duplex modem for transmitting digital data via an analog line as a modem realizing the highest transmission speed.

Further, regarding a half-duplex modem used for a facsimile apparatus, V.V. 27ter (2400bps
~ 4800 bps), V.I. 29 (4800 bps to 96
00 bps), V.I. 17 (7200 bps-14400
In order to be applicable to a facsimile machine as a modem exceeding the transmission speed of ITU-T Recommendation V. 34 half duplex version (2400bps ~ 33600kbp
A revision to s) is in progress.

[0005] The modem device according to this revised version has a facsimile transmission control procedure T.30. 30 and a primary channel for transmitting an image signal. In order to automatically transition between the primary channel and the control channel in response to an incoming signal from a line. Sequence control function is required.

FIG. 34 half duplex (2400 bps
1 to 33600 kbps).

In FIG. 8, reference numeral 8-1 denotes a sequence of the transmitting modem (image transmitting side), and reference numeral 8-2 denotes a sequence of the receiving modem (image receiving side).

Initially, the transmitting modem as well as the receiving modem are connected to 8 procedure exchange and At 34, line probing and training are performed. Here, the modulation modes and functions applicable between the two are determined, and at the same time, by performing line equalization, the parameters (carrier frequency, symbol rate, pre-emphasis coefficient) necessary for transmitting the subsequent primary channel are determined. Etc.).

Subsequently, the transmitting modem operates during (70)
After sending out silence, PPh, ALT, M
By transmitting and receiving the Ph and E signals, line equalization and synchronization with the receiving modem are established, thereby completing preparation for receiving control channel data transmitted from the receiving modem.

When the receiving modem receives the PPh signal from the transmitting modem, it sends out the PPh signal as a response, and then transmits and receives the ALT, MPh, and E signals, thereby
In the same manner as the transmitting modem, line equalization and synchronization with the transmitting modem are established, and preparation for receiving control channel data transmitted from the transmitting modem is completed. Here, the exchange of the MPh signal is performed in order to determine the optimum transmission speed between the transmitting and receiving modems. The signals PPh, ALT, MPh, and E correspond to V. 34 is the same signal as described in FIG.

When preparation for transmission and reception of control channel data is completed by exchanging the PPh to E signals, a transmission control procedure using the control channel is started. In a facsimile apparatus, the T.T. In general, a communication system based on a half-duplex communication system defined in T.30 is used. 30 and revised to V.30. Considerations have been made to accommodate 34 control channels.

When a series of transmission control procedure exchanges (pre-procedures) are completed prior to transmission / reception of an image signal, the transmission / reception modem scrambles the control channel transmission request from the facsimile apparatus when the transmission request is canceled. (Turn-off) for a predetermined period. Subsequently, the transmitting modem
(70 ± 5 msec) during the period (1). After the silent transmission, the transmitting modem transmits a resynchronization signal including S, S _* , PP, and B1 in order to resynchronize with the receiving modem. The suffix * indicates that the signal is an inverted signal of the signal without the suffix.

The receiving modem transmits the scrambled "1".
(Turn-off) After transmission, the receiving modem is resynchronized with the transmitting modem using S, S _* , PP, and B1, and preparation for receiving primary channel data (image signal) transmitted from the transmitting modem is completed. The signals S, S _* , PP, and B1 are V. 34 is the same signal as described in FIG.

When resynchronization is established and preparation for transmission / reception of primary channel data is completed, transmission / reception of image signals using the primary channel is started.

In a conventional facsimile apparatus, a mode (NON-E) in which a binary-coded image signal is transmitted as it is.
CM mode) and a mode (EC) for transmitting in the HDLC format necessary for transmitting an image signal using the error correction function.
M mode). The V.F. With respect to the image signal format when the C.34 is applied, studies are being made mainly on the ECM mode.

When the transmission of the image signal is completed, the transmitting modem transmits scrambled "1" (turn-off) for a predetermined period, and then transmits silence during the period (70 ± 5 msec). The receiving modem is set so that a silent signal (70 ± 5 msec) can be simultaneously detected during reception of the image signal. Upon detecting silence, the receiving modem makes a state transition to control channel data reception.

After transmitting the silence, the transmitting modem controls the post-procedure if the previous primary channel data is the last page of the transmitted document, and if not, exchanges the inter-page procedure with the receiving modem. Restart the channel. By transmitting and receiving the Sh, Sh _* , ALT, and E signals to establish synchronization with the receiving modem, the preparation for receiving control channel data transmitted from the receiving modem is completed.

When the receiving modem receives the Sh signal from the transmitting modem, the receiving modem transmits the Sh signal as a response,
By transmitting and receiving the h _* , ALT, and E signals, in the same manner as the transmitting modem, synchronization with the transmitting modem is established, and preparation for receiving control channel data transmitted from the transmitting modem is completed. Here, in the inter-page procedure, when there is a mode change such as the transmission speed, similar to the previous procedure,
The PPh and MPh signals are used together. In addition, Sh, Sh
_* , ALT, and E signals are 34 is the same signal as described in FIG.

When the preparation for transmission and reception of the control channel data is completed by exchanging the Sh to E signals, the transmission control procedure using the control channel is started. The post-procedure or inter-page procedure based on 30 is exchanged.

When a series of exchanges of transmission control procedures (inter-page procedure or post-procedure) are completed, the transmission / reception modem cancels the control channel transmission request from the facsimile apparatus, thereby scrambled "1" ( (Turn-off) for a predetermined period. after that,
In the case after the inter-page procedure, the silent signal (7
(0 ± 5 msec) After transmission, data transmission by the primary channel and the control channel is repeated, and after the post-procedure, the line is disconnected.

FIG. 9 shows the T.T. 4 shows the details of the HDLC format defined in FIG.

In FIG. 9, reference numeral 9-1 indicates the outline of the frame structure of the primary channel data, which includes a synchronization signal, a partial page, and a partial page control return. The synchronization signal is sent prior to the binary coded information, and includes a training sequence, a nominal value of 200 msec, and an allowable value +
It consists of a continuous flag sequence of 100 msec. However, V. 34, the resynchronization signals S, S _* , P for the primary channel are preceded by the synchronization signal.
Due to the presence of P and B1, it is being considered to omit the training sequence. File data is ECM
This means a partial page in the mode, the image signal is in HDLC format, and a frame number is added.
The maximum number of frames is 256. The partial page control return consists of three consecutive RCP frames as shown at 9-2 in FIG. Further, each RCP frame has a facsimile control field of the HDLC frame set to RCP, as shown at 9-3 in FIG. The facsimile control field of the HDLC format of the partial page including the image signal is FCD.

FIG. 10 shows a state transition diagram of a conventional data demodulation system. Hereinafter, sequence control of a conventional data demodulation system will be described with reference to FIG.

First, in the figure, it is assumed that the data demodulation system of the modem is on the primary channel. This state indicates the state of the receiving modem during the period from to in FIG.
During this period, the transmitting modem is sending out the resynchronization signals S, S _* , PP, and B1, the image signal, and the turn-off sequence, so that the energy of these signals exists in the line.

Therefore, first, after receiving the resynchronization signal, if there is energy in the line, the receiving modem sets 10 in FIG.
According to -1, the state of primary channel data demodulation is held. Subsequently, in the transmitting modem, after a silence signal (70 ± 5 msec), Sh, Sh _* , ALT, E
Then, control channel data is transmitted.

When the receiving modem receives a silent signal to be transmitted when the transmitting modem transitions from the primary channel to the control channel, and determines that there is no energy in the line, the data demodulating system operates as shown in FIG. According to 2, the transition from the primary channel to the control channel is performed. Thereafter, the state of data demodulation of the control channel is maintained until the line runs out of energy.

The above is a description of V.S. This is a conventional method of controlling the sequence from the primary channel to the control channel in the 34 modem.

[0028]

However, in the above conventional example, during reception of the primary channel data, the line energy detector detects a line failure such as an instantaneous interruption during the silent signal period (7).
(0 ± 5 msec), it is erroneously determined that there is no line energy. As a result, even though the primary channel data is being received, the state of the receiving modem transits to demodulation of control channel data. There is a disadvantage that data cannot be demodulated correctly.

Furthermore, since there is no appropriate means for returning from the control channel data demodulation state to the primary channel data demodulation state, there is a disadvantage that the primary channel data cannot be demodulated for a long period of time. .

Therefore, an object of the present invention is to perform sequence control using a criterion other than line energy during reception of primary channel data, whereby the receiving modem erroneously transitions to demodulation of control channel data. In addition, even if the state transitions to the control channel data demodulation state by mistake, by immediately returning to the primary channel data demodulation state, the primary channel data can be continuously received. It is to make.

[0031]

In order to achieve the above object, a first invention according to the present application is based on non-detection / detection of an RCP (partial page control return instruction) frame in primary channel data in an ECM mode. Wherein the receiving modem makes a state transition from a primary channel data demodulation state to a control channel data demodulation state.

Further, the second invention according to the present application is an ECM
RCP in primary channel data in mode
(Partial page control return command) The receiving modem makes a state transition from the primary channel data demodulation state to the control channel data demodulation state based on non-detection / detection of a frame and presence / absence of line energy.

In the third invention according to the present application, the receiving modem changes the primary channel from the control channel data demodulation state based on the detection / non-detection of the synchronization signal of the control data channel within a predetermined time after the line energy is reduced. A state transition is made to a channel data demodulation state.

A fourth invention according to the present invention provides a mode register in an interface with a facsimile apparatus, and when the ECM mode is set in the register, the first or second invention according to the present application. In the case where the ECM mode is not used, the conventional state transition method based on the presence or absence of the line energy is performed, thereby enabling both of them to be selected and used.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram showing a state transition in a first embodiment of the present invention.
9 is a flowchart showing an RCP detection process in the first embodiment.

In FIG. 1, state 100 is a primary channel data demodulation state of the receiving modem, and state 10
Reference numeral 1 denotes a control channel data demodulation state of the receiving modem.

In FIG. 2, step S201 is a data demodulation process for the primary channel.
Reference numeral 2 denotes HDLC deframing processing. Step S203 is an FCS error check, and step S204 is an RCP frame determination. Step S205 is a setting of RCPFLAG, and step S206 is a reset of RCPFLAG.

Hereinafter, the contents of each processing in this embodiment will be described in detail.

When the receiving modem is receiving the primary channel data shown in FIG. 8, the receiving modem holds the primary channel data demodulation state in state 100 in FIG. As described above, in the ECM mode, the primary channel data includes the synchronization signal, the facsimile coded data, and the partial page control return. In particular, the partial page control return of the last part includes three RCP frames.

Therefore, in the case of the ECM mode, if an RCP frame is detected from the demodulation result of the primary channel data, it can be regarded as the end of the image signal. When the receiving modem is in the primary channel data demodulation state state 100, the RCP shown in FIG.
When RCP is detected as a result of the detection processing, 1- in FIG.
The state transits to state 101 by 2. State 101
Then, the receiving modem holds the data demodulation state of the control channel. Conversely, in state 100, RC
When P is not detected, the same state (primary channel data demodulation) is maintained according to 1-1 in FIG.

Next, a detailed RCP detection process will be described with reference to FIG.

First, in step S201, the recommendation V. The data demodulation processing of the primary channel based on the C.34 is performed. This demodulation result is subjected to HDLC deframing processing in step S202. And
As a result of the HDLC deframing process, if an error is found in the HDLC frame, an FCS error occurs.

If there is an FCS error in step S203, the process proceeds to step S206, and the RCP detection process ends. If there is no FCS error, step S
Proceeding to 204, it is determined whether the currently deframed HDLC frame is an RCP frame.

If the frame is not an RCP frame, S2
Proceeding to 06, the RCP detection process ends. If the frame is an RCP frame, the process proceeds to step S205, where RCPFLAG is first set, and RCP frame detection is determined. It is assumed that RCPFLAG is reset before the RCP detection process is started.

Therefore, the sequence control program that controls the state transition of FIG. 1 monitors RCPFLAG in the data demodulation state of the primary channel, and if this flag is set, it is regarded as RCP detection, and the program transits to data demodulation of the control channel. , If it has been reset, it is assumed that RCP has not been detected, and the primary channel state is maintained.

Next, a second embodiment of the present invention will be described.

FIG. 3 is an explanatory diagram showing a transition state in the second embodiment of the present invention. In FIG. 3, state 30
0 is a receiving modem primary channel data demodulation state, and state 301 is a receiving modem control channel data demodulation state.

Next, processing contents in the third embodiment will be described.

When the receiving modem is receiving the primary channel data shown in FIG.
The primary channel data demodulation state is held in state 300 in FIG.

As described above, in the ECM mode, the primary channel data includes a synchronization signal, facsimile coded data, and partial page control return, and in particular, the final partial page control return includes three RCP frames. . Therefore, in the case of the ECM mode, if an RCP frame is detected from the demodulation result of the primary channel data, this can be regarded as the end of the image signal.

In the primary channel data demodulation state state 300, when the RCP is detected as a result of the RCP detection processing shown in FIG. The state transits to state 301 by 2. In state 301, the receiving modem holds the data demodulation state of the control channel.

Conversely, if no RCP is detected in the state 300, the same state (primary channel data demodulation) is maintained according to 3-1 in FIG.

Since the contents of the RCP detection process are the same as in the first embodiment, the description will be omitted.

As described above, in the second embodiment, unlike the first embodiment, not only the RCP detection but also the presence / absence of the line energy is used as a criterion for the state transition of the receiving modem. The transition can be made surely and at the same time as the disappearance of the line energy after the RCP detection (the silent signal period transmitted by the transmitting modem when there is no line failure such as an instantaneous interruption in the middle).

Next, a third embodiment of the present invention will be described.

FIG. 4 is an explanatory view showing a transition state in the third embodiment of the present invention. In FIG. 4, state 40
0 is a receiving modem primary channel data demodulation state, and state 401 is a receiving modem control channel data demodulation state.

FIG. 5 is a flowchart showing the contents of the process of detecting the synchronization signal in the third embodiment. Here, step S501 is the initial value setting of the synchronization signal detection timer T, and step S502 is the data demodulation processing of the control channel. Step S503 is a time-out check process of the timer T, and step S504 is a detection detection / non-detection check of the synchronization signal. Step S505 is a synchronization signal detection flag SYNCF.
This is a set of LAG, and step S506 is SYNC
FLAG is reset. Step S507
Is the end of the synchronization signal detection process.

Hereinafter, the contents of each processing in this embodiment will be described in detail.

First, consider a state immediately after the receiving modem has shifted from the primary channel data demodulation state to the control channel data demodulation state. At this time, the receiving modem is in the state 401 in FIG.

However, in this state, the control channel data is not always transmitted from the transmitting modem. That is, as a result of erroneous RCP detection or instantaneous interruption detection, a transition from the primary channel data demodulation state may occur.

As shown in FIG. 8, the synchronization signal of control channel data transmitted from the transmitting modem
h, Sh _* , ALT, E 34 Recommendations.

Therefore, if a synchronization signal is detected within a specified time from the time when the state transits to the control channel data demodulation state, it is regarded that the state has normally transited from the primary channel data demodulation state to the control channel data demodulation state. Can be.

When the receiving modem detects a synchronization signal as a result of the synchronization signal detection shown in FIG.
1 holds the state 400. Conversely, if the synchronization signal is not detected within the specified time in the state 401, the state transits to the primary channel data demodulation state state 400 according to 4-2 in FIG.

FIG. 5 is a flowchart showing a detailed synchronization signal detecting process. First, in step S501, the recommendation V. The value of about the duration of the synchronization signals Sh, Sh _* , ALT, and E of the control channel data based on 34 is set in the timer T. In step S502, a timeout check of the timer T is performed.

If it is time out, step S
Proceeding to 506, the synchronization signal detection flag SYNCFLAG is reset and the process ends. If the timeout has not occurred, the process proceeds to step S503, where data demodulation processing of the control channel is performed.

The demodulation result is used to determine whether or not a synchronization signal has been detected in step S504. If the result of this determination is that a synchronization signal has been detected, the flow proceeds to step S505, sets SYNCFLAG, and ends in step S507. If no synchronization signal is detected, the process returns to step S502.

Next, a fourth embodiment of the present invention will be described.

The fourth embodiment is an example in which a modem device is incorporated in a facsimile machine. FIG. 6 shows a device configuration in this case, and a portion surrounded by a broken line in FIG. 6 is a modem device.

In FIG. 6, reference numeral 600 denotes a facsimile control system, and reference numeral 601 denotes an I / F circuit in a modem device that interfaces with a facsimile device. Also, 60
Reference numeral 2 denotes a digital signal processor (DSP), and reference numeral 603 denotes a D / A converter (DAC).

Reference numeral 604 denotes a communication band low-pass filter (LPF), and reference numeral 605 denotes an NCU. Reference numeral 606 denotes an amplifier, and 607 denotes a band pass filter (BPF). Reference numeral 608 denotes an A / D converter (ADC).

Hereinafter, the configuration of this embodiment will be described.

The I / F circuit 601 includes a mode register which is a feature of this embodiment. This mode register determines whether or not to provide RCP detection as a criterion at the time of state transition from data demodulation of the primary channel to data demodulation of the control channel.
When the mode is set, the RCP detection
If the mode is not the mode, the mere presence or absence of the line energy is used as a criterion.

The DSP 602 is a device for realizing the sequence control and the modem processing shown in FIG. 1, FIG. 3, FIG. 4, or FIG.

The image data generated by the facsimile control system 600 passes through the I / F circuit 601 to the DSP 602
After that, the baseband signal is converted into a digital modulation signal. The digitally modulated signal is converted into an analog signal by the DAC 603, unnecessary components are removed by the LPF 604, and then sent out to the telephone line via the NCU 605.

The analog modulated signal arriving from the telephone line is amplified by a required amount by an amplifier 606 via an NCU 605, after which an out-of-band component is removed by a BPF 607, and converted into a digital signal by an ADC 608.
Further, the signal is sent to the DSP 602, digitally demodulated, and converted into a baseband signal.

In the figure, DSP 602 to ADC 608,
The feedback path to BPF 607 is A /
The D-conversion timing adjustment and the BPF bandwidth adjustment are performed.
The image signal converted to the baseband is supplied to the I / F circuit 60
1 to the facsimile control system 600.

The sequence control used in the present embodiment is the same as that in the first to third embodiments, and will not be described.

Next, a fifth embodiment of the present invention will be described.

The fifth embodiment is an example in which a modem device is incorporated in a facsimile device. FIG. 7 is an explanatory diagram showing a state transition when the modem device is controlled by the facsimile device in the fifth embodiment. The configuration of the apparatus is assumed to be common to that of FIG.

First, the image signal modem is started up according to 7-1, and the state 700 is entered. In the state 700, the configuration of the modem is set. When this setting is completed, 7--2 in FIG.
As shown in FIG. 8 Start receiving.

Then, V. When the reception of 8 is completed, 7-3
To state 702. Here, V. 8 as a result of reception. If 34 ECM mode is selected,
The ECM mode is set in the ECM setting register of the I / F circuit 601. If the ECM mode is not set, the non-ECM mode is set.

In state 702, control channel data demodulation is continued by 7-4 prior to demodulation of primary channel data as shown in FIG. When the demodulation of the control channel data is completed and the primary channel data is transmitted from the transmission side, a transition is made to the demodulation of the primary channel data in the state 703 according to 7-5, and 7-7 is performed until the control channel data arrives. , The demodulation of the primary channel data is continued.

The transition from primary channel data demodulation to control channel data demodulation according to 7-6 is performed under conditions according to the contents of the ECM mode register.

As described above, by providing the I / F circuit including the ECM mode register inside the modem device, the sequence control method can be selected from outside the device, so that the primary channel data is HDLC-formatted. It is possible to cope with the case where there is no sequence control, and to easily cope with the case where it is desired to use the sequence control of the conventional method.

[0085]

As described above, the first embodiment according to the present application is described.
According to the invention, the detection result of the RCP frame in the ECM mode is used as a criterion for state control of the reception state of the modem, so that even when a line failure such as an instantaneous interruption occurs, the demodulation of the primary channel data and the control channel data can be performed. State transition to demodulation can be performed reliably.

According to the second aspect of the present invention,
By using both the detection result of the RCP frame in the ECM mode and the presence / absence of the line energy as a criterion for state control of the reception state of the modem, even if a line failure such as an instantaneous interruption occurs, the primary channel data demodulation to the control channel can be performed. The state transition to data demodulation is made more reliably and at the same time as the disappearance of the line energy after the RCP detection (silent signal period sent by the transmitting modem when there is no line failure such as instantaneous interruption in the middle). Because it is possible, it is less affected by noise.

According to the third aspect of the present invention,
The receiving modem can transition from the control channel data demodulation state to the primary channel data demodulation state based on the detection / non-detection of the control data channel synchronization signal within a predetermined time after the line energy disappears. It is possible to prevent the demodulation of channel data from becoming impossible.

According to the fourth invention of the present application,
For example, ECM is used for the interface with the facsimile machine.
A mode register is provided, and when the ECM mode is set in the register, the first or second mode according to the present application is set.
When the method according to the present invention is implemented and the mode is not the ECM mode, by implementing the conventional state transition method based on the presence or absence of line energy, both can be selected and used.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a state transition in a first embodiment of the present invention.

FIG. 2 is a flowchart showing an RCP detection process in the first embodiment.

FIG. 3 is an explanatory diagram showing a transition state according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a transition state according to a third embodiment of the present invention.

FIG. 5 is a flowchart showing the content of a synchronization signal detection process in the third embodiment.

FIG. 6 is an explanatory diagram showing a configuration of a facsimile apparatus incorporating a modem device according to a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a state transition when a modem device is controlled by a facsimile device in a fifth embodiment of the present invention.

FIG. It is explanatory drawing which shows the outline | summary of the operation procedure between the primary / control channels in 34 half-duplex communication.

FIG. 9 shows the T.T. recommendation of the ITU-T T series. FIG. 4 is an explanatory diagram showing details of an HDLC format defined in No. 4;

FIG. 10 is an explanatory diagram showing a state transition of a data demodulation system in a conventional modem device.

[Explanation of symbols]

100, 300, 400, 703... Primary channel data demodulation state, 101, 301, 401, 702
... control channel data demodulation state, 700 ...
Configuration setting state, 701. 8 reception state, 704 ... line disconnection state.

Claims (4)

[Claims] 1. A modem device having a primary channel data demodulation state and a control channel data demodulation state, and performing a transition between the above states, wherein a transition from the primary channel data demodulation state to the control channel demodulation state is performed in an ECM mode. RC during operation
A modem device using sequence control that uses a P frame detection result as a criterion. 2. A modem device having a primary channel data demodulation state and a control channel data demodulation state and performing transition between the above states, wherein a transition from the primary channel data demodulation state to the control channel demodulation state is performed in an ECM mode. RC during operation
A modem device using sequence control that uses a P frame detection result and the presence / absence of line energy as a criterion. 3. A modem device having a primary channel data demodulation state and a control channel data demodulation state, and performing a transition between the above states, wherein a transition from the control channel data demodulation state to the primary channel data demodulation state is performed by a line. A modem device using a sequence control that uses as a criterion whether or not a synchronization signal of a control data channel is detected within a predetermined time after energy disappears. 4. The device according to claim 1, further comprising a mode register for selecting a transition mode from the primary channel data demodulation state to the control channel demodulation state, The mode register is set to EC
When the mode is set to the M mode, the sequence control method according to claim 1 or 2 is executed, and when the mode is not the ECM mode, the state transition method according to the presence or absence of the line energy is executed. Modem device.