JP3920182B2 - MODEM DEVICE AND COMMUNICATION DEVICE - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the above-described 2 in a semiconductor DAA (Data Access Arrangement) composed of a primary side circuit connected to a circuit network and a secondary side circuit connected to the primary side circuit via an insulating circuit. When a DSP (Digital Signal Processor) that modulates and demodulates data is connected to the secondary circuit, a modem device that can detect an off-hook of an external telephone without going through the DSP even when the DSP is in an energy saving state The present invention relates to a communication device using the.
[0002]
[Prior art]
In recent years, with the spread of the Internet, digital mobile phones, and the like, communication devices such as mobile terminals and small terminals have been downsized.
[0003]
However, a communication device with a built-in modem connected to a public network requires a relatively large transformer for the purpose of DC insulation for connection to the network, and this transformer hinders downsizing of the communication device. It was a factor.
[0004]
However, with recent advances in semiconductor process technology and isolation technology, semiconductor DAAs that perform network control and the like have been developed, and the function of the lance can be replaced with an extremely small pulse transformer, capacitor, photocoupler, or the like. It has become possible (see Patent Document 1).
[0005]
Such functional elements formed of semiconductors are expected to reduce the size and cost of communication devices, and are being sought for use in communication devices that are not portable terminals such as facsimile devices.
[0006]
Such a communication apparatus requires a network control function for controlling the network, a modulation / demodulation function for performing modulation / demodulation of signals transmitted / received via the network.
[0007]
As described above, the network control function is made semiconductor by the semiconductor DAA, and the modulation / demodulation function is called a so-called modem. Today, a DSP formed by a semiconductor process is used as a main part to perform high-speed processing. Yes.
[0008]
Accordingly, both the network control function and the modulation / demodulation function, which are the minimum functions necessary for communication, are supplied as a semiconductor.
[0009]
[Patent Document 1]
Japanese Patent Laid-Open No. 06-098038
[Problems to be solved by the invention]
However, communication devices are strongly required to reduce power consumption from the viewpoint of environmental considerations, etc., and in order to respond to this, energy saving functions are becoming almost standard equipment. Since it is directly connected to the DSP of the modem device responsible for the modulation / demodulation function, there is a problem that it is impossible to detect the off-hook of the external telephone unless the DSP is supplied with the same power as in the normal state even in the energy saving state.
[0011]
That is, the modem apparatus performs modulation / demodulation of data as described above, but it is necessary to perform modulation / demodulation processing at high speed from the viewpoint of increasing the amount of data to be handled. For this reason, a DSP in which a function responsible for modulation / demodulation is made into a semiconductor is used, and its operating frequency is high. As the operating frequency increases, the power consumption increases accordingly.
[0012]
On the other hand, in the energy saving state, the power supply to the minimum equipment necessary for reception is stopped or suppressed to reduce power consumption. However, the DSP is connected to the semiconductor DAA and detected by the semiconductor DAA. Since the off-hook of the external telephone is informed to the communication apparatus main body side through the DSP, the power supply to the DSP must be supplied in the same manner as in the normal state even in the energy saving state.
[0013]
Therefore, since the semiconductor DAA is used, the power consumption is increased in the state where the same power is supplied to the DSP even during energy saving as compared with the case where the DSP is brought into the energy saving state without using the semiconductor DAA.
[0014]
SUMMARY OF THE INVENTION An object of the present invention is to provide a modem device and a communication device using the same so that off-hook can be detected without going through a DSP during energy saving so that the energy saving effect can be enhanced.
[0015]
[Means for Solving the Problems]
In order to solve the above problems, an invention relating to a modem device includes a primary side circuit connected to a line network and a secondary side circuit connected to the primary side circuit via an insulation circuit. connected to the secondary circuit of the semiconductor DAA transmitting and receiving data includes a DSP for performing modulation and demodulation of data transmitted and received to control the in modem device used by being connected by the communication device main body and the system bus, wherein The storage unit for storing the line voltage when the external telephone is off-hooked as a reference voltage and the line voltage signal and the reference voltage are compared. If they match, it is determined that the external telephone is off-hook. A voltage comparison unit, and a determination result output unit that outputs an off-hook signal indicating that when the external phone is off-hooked by the voltage comparison unit, Is connected to the serial secondary circuit, the power supply to the DSP is when being stopped or suppressed, characterized in that a external telephone off-hook determination circuit for detecting an off-hook of the External telephone.
[0016]
According to another aspect of the present invention, there is provided a communication device comprising a primary circuit connected to a network and a secondary circuit connected to the primary circuit via an insulation circuit, and controls the network and data. A modem device including a semiconductor DAA that transmits / receives data, a DSP that is connected to the secondary circuit and performs modulation / demodulation of data to be transmitted / received, and is connected to the DSP by a system bus to control the semiconductor DAA and the modem device. And a system control unit that communicates with each other and has an energy-saving function that shifts from the normal state to the energy-saving state when the predetermined energy-saving transition requirement is satisfied, and shifts from the energy-saving state to the normal state when the predetermined return requirement is satisfied in the communication apparatus, the modem device, a storage unit for storing the line voltage at the time of off-hook the External telephone as the reference voltage, the line voltage signal and said reference voltage and In comparison, if they match, the voltage comparison unit determines that the external telephone is off-hook, and if the voltage comparison unit determines that the external telephone is off-hook, the off-hook indicating that fact. A determination result output unit for outputting a signal, connected to the secondary side circuit, and when the off-hook of the external telephone is detected when power supply to the DSP is stopped or suppressed, a dedicated line And an external telephone off-hook determination circuit for outputting via the network.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a communication device using a modem device according to the present invention. Note that examples of such a communication apparatus include a facsimile machine, a personal computer, a portable terminal, and the like. In this embodiment, a facsimile machine will be described as an example.
[0018]
The facsimile apparatus includes a system control unit 11. A system bus 12 is connected to the system control unit 11, and a program ROM 13, a data RAM 14, an operation display unit 15, a reading unit 16, a recording unit 17, A clock unit 18 and a modem device 20 are connected, and a semiconductor network control unit 21 based on a semiconductor process is connected to the modem device 20 and connected to a line network.
[0019]
The semiconductor network control unit 21 is formed by a primary side circuit 22 connected to the line network via a diode bridge 27 that rectifies the line current, an insulation circuit 23, and a secondary side circuit 24 connected to the modem device 20. It is a semiconductor DAA.
[0020]
The secondary circuit 24 is provided with a line voltage signal output unit 25 that monitors the line voltage, stores and outputs the line voltage, and the line voltage signal output unit 25 and the system control unit 11 are connected to an external telephone off-hook determination circuit. 26 is connected.
[0021]
A disconnect circuit 28 for controlling whether or not the line network is connected to the external telephone is provided between the diode bridge 27 and the primary side circuit 22, and the external telephone is connected in parallel with the line network. An external telephone terminal 29 is provided so that it can be used.
[0022]
The modem device 20 is configured with a DSP 32 created by a semiconductor process as a main component, and the DSP 32 and the secondary side circuit 24 are connected.
[0023]
The primary side circuit 22 operates by local power supply and includes an A / D-D / A converter (CODEC) 31 that converts an analog signal from the network into a digital signal. Data is exchanged by digital signals, network control such as detection of incoming calls, call processing to the network, driving of the disconnection circuit 28 when the external telephone is off-hook, and transmission / reception of transmission / reception data are performed. Yes.
[0024]
The system control unit 11 controls each component while using the data RAM 14 as a work area according to a control program stored in the program ROM 13.
[0025]
The system control unit 11 enters an energy saving state such as power supply being suppressed at the time of energy saving. When an off-hook or the like of an external telephone is detected at this time, the system control unit 11 returns to a normal state and the detected content In response to this, control is performed so that the device in the energy saving state is returned to the normal state.
[0026]
By the way, the energy saving state is a state in which the operation of devices other than the devices required during reception waiting for an incoming call or the like is stopped or suppressed, and the system control unit 11, the recording unit 17, the reading unit 16, the operation display unit. 15, the DSP 32, the system bus 12, and the like are in an energy saving state, and power supply to these devices is stopped or suppressed during energy saving.
[0027]
As a method for suppressing power supply, for example, the current can be limited or the operating frequency can be lowered. When the operating frequency is changed, the frequency from the clock circuit in the clock unit 18 is lowered.
[0028]
The data RAM 14 temporarily stores the image information read by the reading unit 16 as a file until the image data read by the recording unit 17 is recorded by the recording unit 17. In addition, a buffer page memory (not shown) for developing raw data when storing and recording data is provided so that the memory contents are backed up by a backup circuit (not shown) and stored even when the apparatus is powered off. It has become.
[0029]
The operation display unit 15 includes a numeric keypad for designating a destination telephone number, a start key, a one-touch dial key, and various other keys. The operation display unit 15 includes a display such as a liquid crystal display device, and the operation status of the device to be notified to the user. Display various messages.
[0030]
The reading unit 16 is for obtaining image information by reading a document image at a predetermined reading line density such as 3.85 lines / mm, 7.7 lines / mm, and 15.4 lines / mm. Information is temporarily stored in a line buffer once and transferred to a required device.
[0031]
The recording unit 17 records and outputs the received image information in accordance with the linear density, and records and outputs the image information read by the reading unit 16 in accordance with the linear density (copy operation). Also used for management report output.
[0032]
The clock unit 18 includes a clock circuit that generates a predetermined clock signal and counts the current time. On the other hand, when the time constant set by the system control unit 11 counts down and times out, the system control unit 11 is timed out. Notification is performed and a timer operation is performed.
[0033]
The DSP 32 modulates and demodulates data to be transmitted and received at high speed, and stops or suppresses power supply so that power consumption is suppressed when saving energy.
[0034]
The primary side circuit 22 in the semiconductor network control unit 21 operates by local power supply and controls the network by exchanging data with the secondary side. The secondary side circuit 24 transmits / receives data to / from the DSP 32 and the primary side. It has an interface function that enables transmission and reception with the side circuit 22.
[0035]
Further, the line voltage signal output unit 25 in the secondary side circuit 24 monitors the line voltage, stores the monitored value in the line voltage register 33, converts this value into bits, and sends it to the external telephone off-hook determination circuit 26. Output.
[0036]
The insulating circuit 23 includes a pulse transformer, a capacitor, a photocoupler, and the like, and connects the line network and the secondary side circuit 24 in a state of being galvanically insulated.
[0037]
The external telephone off-hook determination circuit 26 forms the modem device 20 together with the DSP 32. The external telephone off-hook determination circuit 26 includes a storage unit 34, a voltage comparison unit 35, and a determination result output unit 36 as shown in FIG. It is configured.
[0038]
The storage unit 34 stores the line voltage when the external telephone is off-hook as a reference voltage. In Japan, the line voltage drops from about 48V to about 10V when off-hooked, so this reference voltage is, for example, 48V.
[0039]
The voltage comparison unit 35 takes in the value of the line voltage register 33 from the line voltage signal output unit 33 as a line voltage signal and takes in the reference voltage from the storage unit 34 for comparison. If they match, it is determined that the external telephone is off-hook.
[0040]
When the voltage comparison unit 35 determines that the external telephone is off-hooked, the determination result output unit 36 outputs an off-hook signal indicating the fact to the system control unit 11 via the dedicated line 30.
[0041]
With this configuration, when the external telephone is off-hooked in a normal state, the monitor value of the line voltage at that time is stored in the line voltage register 33 of the line voltage signal output unit 25, and the value is used as the line voltage signal by the DSP 32. To the system control unit 11.
[0042]
Then, the system control unit 11 determines whether or not the external telephone is off-hooked from the line voltage register 33. This determination is made by comparing the reference voltage read from the program ROM 13 or the like into the system control unit 11 and the value fetched from the line voltage register 33.
[0043]
When the value fetched from the line voltage register 33 is lower than the reference voltage, it is determined that the external telephone is off-hook, and when it is 48 V, it is determined that the telephone is not off-hook.
[0044]
Of course, the line voltage also decreases when the facsimile apparatus outside performs a predetermined facsimile communication. In this case, however, the communication always involves the system control unit. Accordingly, it can be determined whether or not the line voltage is reduced due to facsimile communication. If the line voltage is reduced when the system control unit is not involved, it is determined that the external telephone is off-hook.
[0045]
On the other hand, when the facsimile apparatus is in the energy saving state, the DSP 32 is also in the energy saving state, so the value of the line voltage register 33 is not sent to the system control unit 11 and the off-hook of the external telephone cannot be detected.
[0046]
Therefore, in the energy saving state, the external telephone off-hook determination circuit 26 is activated, and the value of the line voltage register 33 of the line voltage signal output unit 25 is sent to the voltage comparison unit 35 of the external telephone off-hook determination circuit 26, where A comparison is made with the reference voltage to determine whether the external telephone is off-hook.
[0047]
If it is determined by this determination that the external telephone is off-hook, an off-hook signal indicating that is sent to the system control unit 11 via the dedicated line 30.
[0048]
As a result, the system control unit 11 controls the return from the energy saving state, and sends the control signal of the disconnection circuit 28 to the disconnection circuit 28 via the DSP 32, the secondary side circuit, etc., and disconnects the line network from the facsimile machine body. I do.
[0049]
When the external telephone is on-hooked, the value of the line voltage register 33 becomes a reference voltage such as 48V, so this value is sent to the system control unit 11 via the DSP 32, and the system control unit 11 is connected to the line network. The cutting circuit 28 is controlled so that the facsimile apparatus main body is connected.
[0050]
At this time, if the requirement to shift to the energy saving state is satisfied, control is performed to shift to the energy saving state.
[0051]
As described above, even when the DSP 32 connected to the secondary side circuit is in the energy saving state at the time of energy saving, it becomes possible to detect the off-hook of the external telephone and to prevent the interference between the external telephone and the facsimile apparatus. become.
[0052]
In the above description, when the value of the line voltage register 33 is sent to the external telephone off-hook determination circuit 26, the case where the value of the line voltage register 33 is output as a bit-converted digital signal has been described. However, the line voltage signal output unit 25 may be provided with an A / D converter to convert it into an analog signal and send it.
[0053]
Although providing a new A / D converter in this way increases the cost, the number of connection terminals can be reduced by enabling output as an analog signal, resulting in a cost resulting from these trade-offs. There is an advantage that down is possible.
[0054]
Further, in the configuration in which the line voltage signal is received by the analog signal as described above, the comparison with the reference voltage in the external telephone off-hook determination circuit 26 can be performed by a comparator or the like, so that the circuit configuration can be simplified.
[0055]
In the above description, the case where the modem device 20 is configured by the external telephone off-hook determination circuit 26 and the DSP 32 has been described, but the external telephone off-hook determination circuit 26 may be provided in the system control unit 11. Alternatively, it may be provided in the secondary circuit 24.
[0056]
As described above, when the external telephone off-hook determination circuit 26 is provided in the system controller 11 or in the secondary circuit 26, the system controller 11 and the secondary circuit 26 are formed by a semiconductor process. Therefore, the external telephone off-hook determination circuit 26 can also be formed by a semiconductor process, and there is an advantage that the cost can be reduced as compared with the circuit configuration independently.
[0057]
Further, although the reference voltage is stored in the storage unit 34 of the external telephone off-hook determination circuit 26 to make an off-hook determination, a storage unit corresponding to the storage unit 34 may be provided in the system control unit 11. In this case, the value of the line voltage register 33 is sent to the system control unit 11 via the DSP 32 in the normal state, and the value of the line voltage register 33 is sent to the system control unit 11 via the external telephone off-hook determination circuit 26 in the energy saving state. The system control unit 11 can make an off-hook determination in both the normal state and the energy saving state.
[0058]
Of course, a storage means corresponding to the storage unit 34 may be provided in the line voltage signal output unit 25. in this case,
In the normal state, the value of the line voltage register 33 and the reference voltage are sent to the system control unit 11 via the DSP 32. In the energy saving state, the value of the line voltage register 33 and the reference voltage are controlled by the system via the external telephone off-hook determination circuit 26. It is sent to the unit 11 so that the system control unit 11 can make an off-hook determination in both the normal state and the energy saving state.
[0059]
Next, a second embodiment of the present invention will be described with reference to the drawings. Note that the same components as those in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted as appropriate.
[0060]
In the embodiment described above, the reference voltage is a preset value. However, the line voltage varies depending on the exchange, the line length, etc., and is 48V in Japan, but is different from this value in foreign countries, and also differs depending on the extension exchange.
[0061]
Accordingly, when the reference voltage is set to a fixed value, there is a possibility that off-hook detection of the external telephone cannot be detected due to such a use environment.
[0062]
Therefore, in this embodiment, the reference voltage can be adjusted to prevent the inconvenience that the off-hook of the external telephone cannot be detected depending on the use environment.
[0063]
The reference voltage is adjusted by a user or a serviceman who input from the operation display unit 15 by key input or the like.
[0064]
As a result, even if there is a difference in line voltage due to a difference in environment, it becomes possible to cope with it, and convenience and reliability are improved.
[0065]
FIG. 3 is a flowchart showing an off-hook detection procedure for such an external telephone. First, it is determined whether or not the reference voltage has been changed (step S1). If the reference voltage has been changed, the changed reference voltage is used (step S2).
[0066]
Then, assuming that the reference voltage is A and the value of the line voltage signal from the line voltage signal output unit 25 is B, the difference between them is obtained to determine whether or not the value is positive (steps S3 to S5). .
[0067]
If this difference value is positive, it is determined that the line voltage has become lower than the reference voltage as a result of the line voltage being lowered due to off-hook, and it is determined that the external telephone is off-hook (step S6). 11 side (step S7).
[0068]
As described above, even when the power supply to the modem device 20 is stopped or suppressed during energy saving, the off-hook of the external telephone can be determined, and the energy saving effect is improved and the convenience is improved.
[0069]
Further, by making it possible to change the reference voltage, it becomes possible to set a reference voltage value suitable for the usage environment and the convenience is improved.
[0070]
Next, a third embodiment of the present invention will be described with reference to the drawings. Note that the same components as those in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted as appropriate.
[0071]
In the second embodiment, the reference voltage is set by the user or the like. On the other hand, in this embodiment, automatic setting can be performed.
[0072]
That is, when a user or the like sets a reference voltage, it is necessary to know what value the reference voltage should be set to, and such a value depends on the state of the line network and is difficult for a general user to set. . Therefore, in many cases, such setting must be relied upon by a person having specialized knowledge such as a service person.
[0073]
Therefore, since the line voltage drops when off-hook, the line voltage after the system power is turned on is detected, and a value smaller by a preset ratio (for example, a value of 1/2 or 1/3). ) And set as the reference voltage.
[0074]
However, if the voltage is extremely low, there is a possibility that the external telephone is already off-hooked or disconnected from the line at the time of power supply.
[0075]
FIG. 4 is a flowchart showing a processing procedure for automatically changing such a reference voltage. When the system power is turned on (step S11), the line voltage is monitored (step S12), and the detected value is detected. The reference voltage is calculated and set based on (step S13).
[0076]
In the state where the reference voltage is changed in this way, the reference voltage is set to A, the line voltage from the line voltage signal output unit 25 is set to B, and the difference between them is obtained. Is determined (step S14 to step S16).
[0077]
If this difference value is positive, it is determined that the line voltage has become lower than the reference voltage as a result of the line voltage being lowered due to off-hook, and it is determined that the external telephone is off-hook (step S17). The control unit 11 side is notified (step S18).
[0078]
Note that the line voltage after the power is turned on is detected, then the external telephone is off-hooked, the line voltage at that time is detected, and an intermediate value from the line voltage values before and after the off-hook is set as the reference voltage. It may be.
[0079]
When the reference voltage is automatically set, the system control unit 11 determines that the system power is turned on as described above, so the system control unit 11 is not in the energy saving state but in the normal operation state. Accordingly, the line voltage detection signal is received via the modem device 20.
[0080]
【The invention's effect】
In order to solve the above-described problem, according to the invention relating to the modem device, when the power supply to the DSP of the modem device is stopped or suppressed, the external telephone is connected based on the signal from the secondary circuit of the semiconductor DAA. Since the external telephone off-hook determination circuit for detecting the off-hook and outputting the detection result is provided, the off-hook can be detected without going through the DSP at the time of energy saving, and the energy saving effect can be enhanced.
[0081]
Further, in the invention related to the communication device, power supply to the DSP of the modem device is stopped or suppressed in the energy saving state, and when the off-hook of the external telephone is detected based on a signal from the secondary side circuit during the energy saving state, Since the external telephone off-hook determination circuit for outputting to the system control unit via the dedicated line is provided, the off-hook can be detected without using the DSP during energy saving, and the energy saving effect can be enhanced.
[Brief description of the drawings]
FIG. 1 is a block diagram of a communication device applied to the description of first to third embodiments of the present invention.
FIG. 2 is a block diagram of an external telephone off-hook determination circuit.
FIG. 3 is a flowchart showing an external telephone off-hook determination procedure applied to the description of the second embodiment.
FIG. 4 is a flowchart showing an external telephone off-hook determination procedure applied to the description of the third embodiment.
[Explanation of symbols]
11 System control unit 12 System bus 15 Operation display unit 18 Clock unit 20 Modem device 21 Semiconductor network control unit 23 Insulation circuit 22 Primary side circuit 24 Secondary side circuit 25 Line voltage signal output unit 26 External telephone off-hook determination circuit 28 Disconnection Circuit 29 External telephone terminal 30 Dedicated line 32 DSP
33 Line voltage signal output unit 33 Line voltage register 34 Storage unit 35 Voltage comparison unit 36 Determination result output unit

Claims (20)

The semiconductor DAA 2 includes a primary circuit connected to a network and a secondary circuit connected to the primary circuit via an insulating circuit, and controls the network and transmits / receives data. In a modem device which is connected to a communication device main body and used by a system bus, and has a DSP which modulates and demodulates data to be transmitted / received by being connected to a secondary circuit,
A storage unit for storing a line voltage when the external telephone is off-hook as a reference voltage;
A voltage comparison unit that compares the line voltage signal and the reference voltage and determines that the external telephone is off-hook when they match;
When the voltage comparison unit determines that the external telephone is off-hook, the voltage comparison unit includes a determination result output unit that outputs an off-hook signal indicating that,
A modem connected to the secondary circuit and provided with an external telephone off-hook determination circuit for detecting an off-hook of the external telephone when power supply to the DSP is stopped or suppressed apparatus. The secondary circuit includes a line voltage register that monitors and stores the line voltage, and has a line voltage signal output unit that outputs a signal corresponding to the line voltage register value as a line voltage signal;
2. The modem apparatus according to claim 1, wherein the external telephone off-hook determination circuit determines whether or not the external telephone is off-hook based on the line voltage signal.   3. The modem apparatus according to claim 2, further comprising a D / A converter that converts the line voltage register value into an analog signal and outputs the analog signal to the external telephone off-hook determination circuit.   When the external telephone off-hook determination circuit determines that the external telephone is off-hook based on the line voltage signal, the determination result is output to the communication device body via a dedicated line. Item 4. The modem device according to any one of Items 1 to 3. 5. The modem device according to claim 1, wherein the reference voltage value in the storage unit is adjustable. 6. The modem device according to claim 5 , wherein a user sets the value of the reference voltage.   When adjusting the value of the reference voltage, the external telephone is set in an off-hook state, the line voltage at that time is detected, and the value of the reference voltage is determined and set based on the voltage. Item 7. The modem device according to Item 5 or 6. When setting the reference voltage value by detecting the line voltage at the time when the external telephone is set to the off-hook state, a value smaller by a preset ratio than the value of the line voltage detected in the off-hook state is set. The modem device according to claim 7 , wherein the modem device is set as a value of the reference voltage. When adjusting the value of the reference voltage, the line voltage in the off-hook state is detected, and the lowest voltage at that time is also detected, and the voltage between the line voltage in the off-hook state and the lowest voltage is detected. 8. The modem device according to claim 7 , wherein the modem device is set to a value of the reference voltage. A semiconductor DAA which comprises a primary side circuit connected to a line network and a secondary side circuit connected to the primary side circuit via an insulation circuit, which controls the line network and transmits / receives data; A modem device having a DSP connected to the secondary side circuit for performing modulation / demodulation of data to be transmitted and received, and a system control unit connected to the DSP by a system bus to control and communicate with the semiconductor DAA and the modem device In a communication device with an energy saving function that shifts from a normal state to an energy saving state when a predetermined energy saving transition requirement is satisfied, and shifts from an energy saving state to a normal state when a predetermined return requirement is satisfied,
The modem device is
A storage unit for storing a line voltage when the external telephone is off-hook as a reference voltage;
A voltage comparison unit that compares the line voltage signal with the reference voltage and determines that the external telephone is off-hook when they match;
When the voltage comparison unit determines that the external telephone is off-hook, the voltage comparison unit includes a determination result output unit that outputs an off-hook signal indicating that,
An external telephone off-hook determination circuit that outputs via a dedicated line when an off-hook of the external telephone is detected when the power supply to the DSP is stopped or suppressed while being connected to the secondary circuit. A communication apparatus comprising: The secondary circuit includes a line voltage register that monitors and stores the line voltage, and has a line voltage signal output unit that outputs a signal corresponding to the line voltage register value as a line voltage signal;
11. The communication apparatus according to claim 10, wherein the external telephone off-hook determination circuit determines whether or not the external telephone is off-hook based on the line voltage signal.   12. The communication apparatus according to claim 11, further comprising a D / A converter that converts the line voltage register value into an analog signal and outputs the analog signal to the external telephone off-hook determination circuit.   When the external telephone off-hook determination circuit determines that the external telephone is off-hook based on the line voltage signal, the determination result is output to the communication device body via a dedicated line. Item 13. The communication device according to any one of Items 10 to 12.   The communication apparatus according to claim 10, wherein a value of the reference voltage in the storage unit is provided to be adjustable.   The communication apparatus according to claim 14, wherein a user sets the value of the reference voltage.   When adjusting the value of the reference voltage, the external telephone is set in an off-hook state, the line voltage at that time is detected, and the value of the reference voltage is determined and set based on the voltage. Item 16. The communication device according to Item 14 or 15.   When setting the reference voltage value by detecting the line voltage at the time when the external telephone is set to the off-hook state, a value smaller by a preset ratio than the value of the line voltage detected in the off-hook state is set. The communication apparatus according to claim 16, wherein the communication apparatus sets the reference voltage value.   When adjusting the value of the reference voltage, the line voltage in the off-hook state is detected, and the lowest voltage at that time is also detected, and the voltage between the line voltage in the off-hook state and the lowest voltage is detected. The communication apparatus according to claim 16, wherein the communication apparatus sets the reference voltage value.   The communication apparatus according to claim 10, wherein the external telephone off-hook determination circuit, the DSP, and the secondary circuit are formed on the same semiconductor chip.   The communication apparatus according to claim 10, wherein the off-hook signal is transmitted to the system control unit to cancel the energy saving state.

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