JP3387804B2 - Interface circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interface circuit provided between a primary side circuit and a secondary side circuit, electrically separating the two circuits and transmitting / receiving a signal between the two circuits. Is a terminal network that is connected to a center-side device using a telephone line, performs no ringing communication with the center-side device, and automatically reads meters for LP gas, city gas, electricity, water, etc. The present invention relates to an interface circuit provided between a control device and a meter.

[0002]

2. Description of the Related Art In a no-ringing communication system to which a conventional terminal network control device is applied, as shown in FIG. 6, a center side device 1 is a host device 2 and a center side network control device 3 is used.
In the terminal-side device 4 installed in the customer, a terminal network control unit (hereinafter referred to as “NCU”) 5 is connected with a meter 6, a security device 7, and a home telephone 8. . The center-side device 1 is connected to a center-side switching center (LS) 10 via a subscriber telephone line 9, and the terminal-side device 4 is connected to a center-side exchange provided with a no ringing trunk (NRT) 12 via a subscriber telephone line 11. It is connected to the station (LS) 13. The center-side switching center 10 and the terminal-side switching center 13 are connected to each other by an inter-station relay line 14
Are connected to each other.

In such a configuration, the NCU 5 performs no ringing communication with the center side device 1 via the no ringing trunk 12 and each telephone line. NCU5
Sends meter reading data detected by the meter 6 to the center apparatus 1 in response to a command from the center apparatus 1, or sends meter reading data by dialing the center apparatus 1 upon activation from the meter 6.

Here, it is stipulated by law that the NCU 5 and the meter 6 are electrically insulated (isolation) in order to prevent noise from being mixed in from a connecting line, and an interface circuit for that purpose is provided in the NCU 5. It is provided. The interface circuit may be provided inside the meter 6 or between the NCU 5 and the meter 6.

FIG. 7 is a diagram showing the interface circuit. Briefly explaining the operation of the interface circuit, the signal transmitted from the NCU 5 (primary side circuit) to the meter 6 (secondary side circuit) is transmitted by setting the terminal D _OUT to low level. That is, the terminal D _OUT
Is set to the low level, the switching transistor (hereinafter, the switching transistor is simply referred to as “transistor”) Tr1 is turned on, and the photocoupler PH1 is driven thereby. This photo coupler PH1 is NC
U5 and the meter 6 are electrically insulated.

The transistor Tr2 is turned on by driving the photocoupler PH1, and the power supply voltage of the battery Bt supplied to the collector side of the transistor Tr2 is output to the emitter terminal. As a result, a high level signal is input to the meter 6 side through the terminal DT. In this way, when the signal is transmitted from the NCU 5 to the meter 6, the power supply voltage of the battery Bt is supplied to the meter 6 side,
It is not supplied to the U5 side.

On the other hand, the signal transmitted from the meter 6 to the NCU 5 is transmitted by setting the terminal DT to high level. That is, when a high level signal is input from the terminal DT, the high level signal is divided by the resistors R4 and R5 to turn on the transistor Tr3. This drives the photocoupler PH3. The photocoupler PH3 also electrically insulates the NCU 5 from the meter 6.

The photocoupler PH3 has a battery Bt.
Since the power supply voltage of the photo coupler PH3
Current flows through the photodiode of. Therefore, the collector side of the phototransistor of the photocoupler PH3 becomes low level. As a result, a low level signal is input to the NCU 5 side through the terminal D _IN . Thus, even when the signal is transmitted from the meter 6 to the NCU 5, the power supply voltage of the battery Bt is not supplied to the NCU 5 side.

When a signal is transmitted from the NCU 5 to the meter 6, a high level signal is output to the terminal DT. At this time, the high level signal spills around to drive the transistor Tr3 to drive the terminal D. Output low level signal to _IN . Therefore, when a signal is transmitted from the NCU 5 to the meter 6, control is performed so that the signal input to the terminal D _IN is not accepted on the NCU 5 side.

[0010]

As described above, in the above interface circuit, since the power supply voltage of the battery Bt is not supplied to the NCU 5 side, the remaining capacity of the battery Bt is directly known from the NCU 5 side. There is a problem that you can not. Therefore, the battery Bt
If the capacity of the battery decreases with the lapse of time, a sufficient voltage for driving the circuit on the meter 6 side cannot be output to the terminal DT. Therefore, although the NCU 5 is sufficiently operable, it may not be possible to communicate with the meter 6.

In view of the above problems, the present invention can detect the state of the power supply voltage of the battery for operating the interface circuit from the primary side circuit, and can always perform good communication between the primary side circuit and the secondary side circuit. The purpose is to provide a circuit.

[0012]

Means for Solving the Problem The problem solving means according to the present invention is provided between a primary side circuit and a secondary side circuit, electrically separates both circuits, and transmits and receives a signal between both circuits. In the interface circuit to perform, the insulating and transmitting means for electrically insulating the input side and the output side and transmitting the signal between the input and output, the voltage supply means for supplying the power supply voltage for operation, and the signal from the primary side circuit It is provided with a voltage detection means for detecting the state of the power supply voltage when input, and an output means for outputting the detection result of the voltage detection means to the primary side circuit.

According to the above configuration, when the signal is input from the primary side circuit, the state of the power supply voltage for operation is detected, and the detection result is output to the primary side circuit. for that reason,
A state of the power supply voltage for operating the interface circuit, for example, a decrease in the power supply voltage can be detected in the primary side circuit.

Here, when detecting the state of the power supply voltage for operation, a switch element is used for outputting the power supply voltage to the secondary side circuit based on a signal input from the primary side circuit. With this configuration, the switch element does not turn on when no signal is input from the primary side circuit, so the power supply voltage is not output to the secondary side circuit, and the power supply voltage status is maintained only when a signal is input from the primary side circuit. Can be detected. Therefore, when the power supply voltage is composed of, for example, a battery, its consumption can be suppressed.

If the voltage detecting means detects the voltage at the output end of the switch element, the voltage detecting means can detect a value which is the closest to the value of the power supply voltage, so that accurate voltage detection can be performed.

The above-mentioned interface circuit is provided between the terminal network control device for performing data communication with the center side device and the terminal equipment connected thereto, and electrically connects between the terminal network control device and the terminal equipment. In an interface circuit that separates into two and transmits and receives signals between them, an insulating photocoupler that electrically insulates between the terminal network control device and the terminal equipment and that transmits signals between the two,
A battery that supplies a power supply voltage for operating the interface circuit, and a switching transistor that outputs the power supply voltage supplied by the battery to the terminal equipment based on a signal input from the terminal network control device through the insulating photocoupler. And a voltage detection means for detecting the state of the voltage output from the output terminal to the terminal device by the switching transistor, and an output for outputting the detection result to the terminal network control device when the voltage detection means detects a voltage drop. And an output unit composed of a photo coupler for use.

A Zener diode can be used as the voltage detecting means. Further, the voltage detection means is composed of a voltage detection circuit that outputs a drive signal to the output means when a voltage having a value lower than a predetermined reference value is input, or the voltage detection means has its input terminal. When a voltage higher than the predetermined reference value is input, the output terminal is set to that voltage and the output means is not driven, and when a voltage lower than the reference value is input, the output terminal is lower than that voltage. It may be composed of a voltage detection circuit for converting the voltage into a voltage and driving the output means.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

<First Embodiment> A system configuration to which a terminal network control device having an interface circuit according to the first embodiment of the present invention is applied is the same as the configuration shown in FIG. Basically the same. Therefore, FIG. 6 will be referred to again in the following description.

FIG. 2 is a block diagram showing an internal configuration of the terminal network control unit (hereinafter referred to as "NCU") 5 shown in FIG. The NCU 5 includes a pole detection circuit 21, a rectifier circuit 22, an off-hook control circuit 23, a PB that detects a pole signal.
PB transmitter / receiver circuit 2 for transmitting / receiving (push button) signals
4, a main controller 25 having a microcomputer, a connection switching circuit 26 for connecting or disconnecting the home telephone 8 to and from the subscriber telephone line 11, a modem 27, an off-hook detection circuit 28 for detecting the use state of the home telephone 8, a meter 6 Also, interface circuits 29 and 30 that control the interface with the security device 7, an oscillator circuit 31 including a crystal oscillator, and a main controller 25 as necessary.
Is constituted by a reset circuit 32 for resetting, a EEPROM 33 for storing data for operating the main controller 25, and a power supply circuit 34.

FIG. 1 is a diagram showing the interface circuit 29 shown in FIG. Terminal D connected to NCU5
_OUT is connected to the base terminal of a switching transistor Tr1 (hereinafter, the switching transistor is simply referred to as "transistor"). Transistor T
The emitter terminal of r1 is connected to the anode terminal of the photodiode of the photocoupler PH1 which is an insulating and transmitting means for electrically insulating the input side and the output side and transmitting a signal between the input and the output. The V _CCM terminal to which the supply voltage from the NCU5 side is input is connected to the collector terminal of the transistor Tr1 and the supply voltage is supplied to the transistor Tr1.

The collector terminal of the phototransistor of the photocoupler PH1 is connected to the base terminal of the transistor Tr2 via the resistor R1. The collector terminal of the transistor Tr2 is connected to the positive terminal of the battery Bt as a voltage supply means for supplying a power supply voltage for operation.

As the battery Bt, a primary battery which needs to be replaced, for example, a lithium battery is used. Instead of this, a secondary battery that can be used again by charging may be used.

At the emitter terminal of the transistor Tr2,
The terminal DT connected to the meter 6 is connected via the resistor R2, and is also connected to the anode terminal of the photodiode of the photocoupler PH2 via the resistor R3. The cathode terminal of this photodiode is the battery Bt
Is connected to the cathode terminal of the Zener diode Zn as a voltage detecting means for detecting the power supply voltage of the. The collector terminal of the phototransistor of the photocoupler PH2 is connected to the V _CCM terminal via the resistor R7 and the output terminal BtH / L. That is, the photocoupler PH2 includes the Zener diode Z.
It functions as an output unit that outputs the result of the voltage detection by n to the NCU 5.

On the other hand, the terminals DT and SG connected to the meter 6 are divided by resistors R4 and R5, and the division point is
It is connected to the base terminal of the transistor Tr3 via the resistor R6. Note that SG indicates a signal ground on the meter 6 side. The collector terminal of the transistor Tr3 is connected to the battery Bt via the photodiode of the photocoupler PH3, which is an insulating and transmitting means, and the resistor R8. The collector terminal of the phototransistor of the photocoupler PH3 is connected to the terminal D _IN connected to the NCU 5 and also to the V _CCM terminal via the resistor R9.

Further, the cathode terminal of the photodiode of the photocoupler PH1 is connected to the ground on the NCU5 side via the resistor R10, and the photocouplers PH2 and PH2 are connected.
The emitter terminals of the phototransistors 3 are also connected to the ground on the NCU 5 side.

The terminal SG is connected to the emitter terminal of the phototransistor of the photocoupler PH1, the negative terminal of the battery Bt, the emitter terminal of the transistor Tr3 and the anode terminal of the Zener diode Zn.

First, a case where a signal is transmitted from the NCU 5 (primary side circuit) to the meter 6 (secondary side circuit) by the above connection configuration will be described. When a low level signal is input to the terminal D _OUT from the main control unit 25 of the NCU 5, the transistor Tr1 turns on. When this is turned on, the photo coupler P
A current flows through the photodiode of H1 to turn on the phototransistor. As a result, the transistor Tr2 is turned on, and the power supply voltage of the battery Bt supplied to the collector terminal of the transistor Tr2 is output to the emitter terminal (see point A in FIG. 1) and supplied to the terminal DT on the meter 6 side. Therefore, a high level signal is output to the terminal DT.

At this time, the voltage at the output point A which is the output end of the emitter terminal of the transistor Tr is detected by the Zener diode Zn. That is, when the power supply voltage of the battery Bt is normal, a current flows through the photodiode of the photocoupler PH2, the phototransistor is turned on, and a low level signal is output to the output terminal BtH / L.

On the other hand, when the value of the power supply voltage of the battery Bt is lower than the value of the terminal voltage of the Zener diode Zn (for example, 2.0 V), the Zener diode Zn is not turned on. Therefore, since no current flows in the photodiode of the photocoupler PH2, the photocoupler PH2
2 does not drive. Therefore, the phototransistor of the photocoupler PH2 is not turned on, and the output terminal BtH / L remains high level and does not change.

The signal at the output terminal BtH / L is NC
It is input to the main control circuit 25 of U5. Then, the main control circuit 25 determines that the power supply voltage of the battery Bt is lowered when the output terminal BtH / L is at the high level when the low level signal is output from the terminal D _OUT . Therefore, the decrease in the power supply voltage of the battery Bt can be detected from the NCU 5 side.

Then, the main control circuit 25 causes the battery Bt to
The user can know the consumption of the battery Bt by discriminating the decrease in the power supply voltage of the battery and, for example, notifying and displaying the information to the outside. It can be used.
Therefore, the NCU 5 can always perform good communication with the meter 6.

FIG. 3 is a diagram showing a timing chart of signals at the terminal D _OUT , the output point A and the terminal DT. As shown in the figure, the logics of the signal at the terminal D _{OUT and} the signal at the output point A and the terminal DT have an inverse relationship.

Here, in the signal level at the output point A and the terminal DT, the signal level at the terminal DT is slightly lower than the signal level at the output point A (the dotted line shows the signal level at the output point A). This is due to the value of the resistor R2 interposed between the output point A and the terminal DT and the impedance of the circuit on the meter 6 side. Therefore, in the present embodiment, the power supply voltage is detected at the output point A of the emitter terminal which is the output terminal of the transistor Tr2,
The value that is the closest to the actual voltage of the battery Bt can be detected. Therefore, more accurate voltage detection can be performed.

Therefore, according to the above interface circuit, the battery Bt power supply voltage is not always detected, but only when the transistor Tr2 is turned on, that is, when the low level signal is input to the terminal D _OUT. The power supply voltage of Bt is detected. That is, when the transistor Tr2 is in the off state, no current flows in the photocoupler PH2, so the power supply voltage of the battery Bt is not detected. Therefore, consumption of the battery Bt can be suppressed, and an economical circuit can be obtained.

Further, for example, a Zener diode Zn
When becomes defective, the photocoupler PH2 is not driven. Therefore, since the high level signal is held at the output terminal BtH / L, a highly reliable voltage detection circuit considering fail safe can be obtained.

The interface circuit described above has the same function even when the connection of the resistor R3, the photodiode of the photocoupler PH2, and the Zener diode Zn is replaced with each other. Furthermore, if the resistance value of the resistor R3 and the value of the forward current of the photodiode of the photocoupler PH2 are changed to appropriate values, the Zener diode Zn can be omitted from the relationship between the battery voltage and the detection voltage level.

The case of transmitting a signal from the meter 6 to the NCU 5 will be described. For example, from the meter 6 to the terminal DT.
When a high-level signal is input to R1, the high-level signal divided by the resistors R4 and R5 is input to the base terminal of the transistor Tr3 via the resistor R6. Then, the transistor Tr3 is turned on, a current flows through the photodiode of the photocoupler PH3, the phototransistor of the photocoupler PH3 is turned on, and the terminal D _IN becomes low level.
Further, when a low level signal is input to the terminal DT, the transistor Tr3 does not turn on, so the terminal D _IN becomes high level. In this way, the signal is transmitted from the meter 6 to the NCU 5.

In the first embodiment, instead of the photocoupler PH2, an element capable of transmitting the amount of current flowing in the photodiode to the NCU 5 as an analog amount may be used. That is, for example, the amount of current flowing through the photodiode is proportional to the amount of light emitted from the photodiode, so that the phototransistor receives the amount of light received according to the amount of light emitted, and the amount of light received is maintained as is in the NCU.
Transmit to 5. Then, the capacity of the power supply voltage of the battery Bt can be grasped before the power supply voltage of the battery Bt is lowered and detected. Therefore, the battery Bt can be replaced and the charging device can be prepared in advance.

<Second Embodiment> FIG. 4 is a diagram showing an interface circuit according to the second embodiment. The interface circuit of the second embodiment is characterized in that the voltage detecting means for detecting the power supply voltage of the battery Bt is provided in the photocoupler PH2 for outputting to the NCU 5 when a voltage lower than a predetermined reference value is input. In contrast, a voltage detection circuit that outputs a drive signal, for example, a voltage detection IC / DK is used.

The voltage detection IC DK has its input terminal DK
_{If the} voltage V _IN input to _IN is higher than a predetermined reference value V _S (for example, V _S = 2.0 V), the output terminal D
Output a low level signal to K _OUT and input voltage V _IN
Is a voltage lower than the reference value V _S, the IC outputs a high level signal to the output terminal DK _OUT . However, in this case, the value of the high-level voltage becomes the value of the input voltage V _IN .

In the second embodiment, the input terminal DK _IN of the voltage detection IC / DK has the transistor Tr.
2 is connected to the emitter terminal and its output terminal DK
_OUT is connected to the anode terminal of the photodiode of the photocoupler PH2 via the resistor R3. The cathode terminal of the photodiode is connected to the terminal SG, and the ground terminal DK _G of the voltage detection IC / DK is also the terminal SG.
It is connected to the. Regarding other connection configurations,
It is similar to the embodiment.

With this connection configuration, when the power supply voltage of the battery Bt is normal, the transistor Tr2 is turned on and the normal voltage is input to the input terminal DK _IN of the voltage detection IC / DK. At this time, since the voltage V _IN input to the input terminal DK _IN is higher than the reference value V _S , the output terminal DK _OUT
A low level is output to. Therefore, the photocoupler PH2 does not operate, and the terminal BtH / L remains high level.

On the other hand, the power supply voltage of the battery Bt is lowered and the voltage of the emitter terminal of the transistor Tr2 is changed to the reference value V _S.
If the following occurs, the voltage detection IC / DK output terminal DK _OUT
A voltage value that is substantially the same as the value of the input voltage V _IN is output to. Specifically, from the value of the input voltage V _IN , the voltage V _t (eg,
A voltage (V _IN −V _t ) obtained by subtracting V _t = 0.1 V is output. Therefore, a current corresponding to the voltage (V _IN −V _t ) flows through the photodiode of the photo coupler PH2.

This current turns on the photodiode of the photocoupler PH2, which turns on the phototransistor to bring the terminal BtH / L to the low level and N
The main controller 25 of the CU 5 can detect the voltage drop of the battery Bt.

The output terminal DK of the voltage detection IC / DK
_{From OUT} , a voltage equal to or lower than the value of the voltage V _IN input to the input terminal DK _IN may be output as long as it is within the range in which the photodiode of the photocoupler PH2 is turned on.

Therefore, when the signal is transmitted from the NCU 5 to the meter 6, if the power supply voltage of the battery Bt is normal, a low level signal is output from the output terminal DK _OUT of the voltage detection IC / DK, and a current is supplied to the photocoupler PH2. Does not flow. Then, a current flows through the photocoupler PH2 only when the power supply voltage of the battery Bt drops. Therefore, as compared with the case where a current flows through the photocoupler PH2 when the power supply voltage is normal as in the first embodiment, there is an advantage that the consumption of the battery Bt is further suppressed and it is economical.

The interface circuit shown in FIG. 4 has the same function even if the connection of the resistor R3 and the photodiode of the photocoupler PH2 is interchanged.

<Third Embodiment> FIG. 5 is a diagram showing a third embodiment of the present invention. The interface circuit of the third embodiment is characterized in that, when a voltage having a value higher than a predetermined reference value is input from its input terminal to the voltage detection means for detecting the power supply voltage of the battery Bt, the output terminal is set to that voltage. Photocoupler PH2 for outputting to NCU5
When a voltage lower than the reference value is input without driving the voltage detector, a voltage detection circuit for driving the photocoupler PH2 by setting the output terminal to a voltage lower than the voltage, for example, a reset IC Rs is used. In point.

When the input voltage V _IN input to the input terminal Rs _IN is higher than a predetermined reference value V _S (for example, V _S = 2.0V), the reset IC Rs outputs the output terminal Rs _OUT at a high level. If the input voltage V _IN is equal to or lower than the reference value V _S , the output terminal Rs _OUT is a low level IC. However, in this case, the value of the high-level voltage becomes the value of the input voltage V _IN .

In the connection configuration to which the reset IC Rs is applied, the emitter terminal of the transistor Tr2 is connected to the input terminal Rs _IN of the reset IC Rs and the anode terminal of the photodiode of the photocoupler PH2 is connected. There is. Output terminal Rs of reset IC / Rs
_OUT is connected to the cathode terminal of the photodiode via a resistor R3. The ground terminal Rs _G of the reset IC Rs is connected to the terminal SG. Other configurations are similar to those of the first embodiment.

With this connection configuration, when the battery voltage of the battery Bt is normal, the transistor Tr2 is turned on and the normal voltage is input to the input terminal Rs _IN of the reset IC Rs. At this time, since the voltage V _IN input to the input terminal Rs _IN is higher than the reference value V _S , the output terminal Rs _OUT
A high level is output to. Therefore, since the photocoupler PH2 is not driven, the terminal BtH / L remains high level.

On the other hand, when the value of the battery voltage of the battery Bt decreases and becomes equal to or lower than the reference value V _S , the output terminal Rs _OUT of the reset IC Rs has the same voltage (low level) as the voltage of the terminal SG. Is output. By the output of this voltage,
Current flows through the photodiode of the photocoupler PH2,
The phototransistor turns on, and the terminal BtH / L becomes low level. As a result, main controller 25 of NCU 5 can detect a decrease in the power supply voltage of battery Bt.

Output terminal Rs of reset IC Rs
_{As for} the value of the voltage output to _OUT , a voltage higher than the low level may be output as long as the photodiode of the photocoupler PH2 is turned on.

Therefore, also in the third embodiment, as in the second embodiment, when a signal is transmitted from the NCU 5 to the meter 6, a current flows through the photocoupler PH2 only when the power supply voltage of the battery Bt drops. Therefore, there is an advantage that the consumption of the battery Bt is further suppressed and it is economical compared to the first embodiment in which a current flows through the photocoupler PH2 when the power supply voltage of the battery Bt is normal.

Since the photodiode of the photocoupler PH2 is directly connected to the emitter terminal of the transistor Tr2, the reference value V _S which is the detection level of the voltage at which the photodiode of the photocoupler PH2 turns on is
Compared with the second embodiment, there is an advantage that the voltage can be lowered by the voltage Vt corresponding to the internal resistance of the voltage detection IC / DK. Therefore, the battery Bt can be used for a long time, and the cost can be reduced.

The interface circuit shown in FIG. 5 has the same function even if the connection of the resistor R3 and the photodiode of the photocoupler PH2 is interchanged.

The present invention is not limited to the above embodiment, and many modifications and changes can be added to the above embodiment within the scope of the present invention. For example, in the above embodiment, the power supply voltage of the battery is detected when the signal is transmitted from the NCU to the meter, but the power supply voltage of the battery is detected when the signal is transmitted from the meter to the NCU. Good.

The interface circuit may be provided in the meter, or NCU.
And the meter may be provided independently. In the above embodiment, the interface circuit with the meter has been described, but the interface circuit may be applied to the interface circuit with the security device. Further, instead of the photocoupler in the interface circuit, a relay, a transformer or the like may be used as long as the response speed of the signal does not affect the conditions.

[0060]

As described above, according to the present invention, when a signal is input from the primary side circuit, the state of the power supply voltage for operation can be detected and the detection result can be output to the primary side circuit. Therefore, the state of the power supply voltage can be detected in the primary side circuit. Therefore, for example, if a battery is used as a power supply and it is exhausted, the battery can be replaced or recharged, and the primary side circuit can always provide good communication with the secondary side circuit. can do.

When detecting the state of the power supply voltage,
If a switch element that outputs the power supply voltage to the secondary side circuit based on the signal input from the primary side circuit is used, the switch element does not turn on when no signal is input from the primary side circuit, so detection is not performed. Therefore, the state of the power supply voltage can be detected only when a signal is input from the primary side circuit. Therefore, since it is not always detected, the consumption of the power source can be suppressed, the life of the power source can be extended, and as a result, the cost can be reduced.

Furthermore, if a circuit that operates when the power supply voltage becomes lower than the reference value is used, the decrease is detected only when the power supply voltage decreases, so that the power consumption can be further suppressed and the cost can be further reduced. Can be reduced.

Further, if the voltage at the output end of the switch element is detected, the value that is the closest to the supply voltage value of the power supply voltage can be detected, so that accurate voltage detection can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing an interface circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a terminal network control device to which an interface circuit is applied.

FIG. 3 is a diagram showing a timing chart of an interface circuit.

FIG. 4 is a diagram showing an interface circuit according to a second embodiment.

FIG. 5 is a diagram showing an interface circuit according to a third embodiment.

FIG. 6 is a diagram showing a configuration of a no ringing communication system.

FIG. 7 is a diagram showing a conventional interface circuit.

[Explanation of symbols]

5 Terminal network controller 6 gas meters Bt battery DK voltage detection IC Rs reset IC PH1, PH2, PH3 Photo coupler Tr2 switching transistor Zn Zener diode

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) G08C 13/00-17/02 G08C 19/00-23/04 G08C 25/00-25/04 H03J 9/00-9 / 06 H04M 11/00-11/10 H04Q 9/00-9/16

Claims (7)

(57) [Claims] 1. An interface circuit provided between a primary side circuit and a secondary side circuit, for electrically separating the two circuits and for transmitting and receiving a signal between the two circuits, wherein an input side and an output side are electrically connected. Electrically insulating and transmitting means for transmitting a signal between input and output, a voltage supplying means for supplying a power supply voltage for operation, and a state of the power supply voltage when a signal is input from the primary side circuit. An interface circuit comprising: a voltage detection unit for detecting the voltage; and an output unit for outputting the detection result of the voltage detection unit to the primary side circuit. 2. A switch element for outputting the power supply voltage supplied by the voltage supply means to the secondary side circuit based on a signal input from the primary side circuit through the insulating and transmitting means, and the voltage detecting means, The interface circuit according to claim 1, wherein a voltage output to the secondary side circuit is detected by the switch element. 3. The interface circuit according to claim 2, wherein the voltage detecting means detects the voltage at the output end of the switch element. 4. A terminal network control device that performs data communication with a center-side device and a terminal device connected to the terminal network control device, electrically separates the terminal network control device and the terminal device, and both. In an interface circuit for transmitting and receiving a signal between the terminal network control device and the terminal device, an insulating photocoupler for electrically insulating between the terminal network control device and the terminal device, and a power supply voltage for operating the interface circuit , A switching transistor for outputting a power supply voltage supplied by the battery to the terminal device based on a signal input from the terminal network control device through an insulating photocoupler, and the switching transistor Voltage detecting means for detecting the state of the voltage output from the output terminal to the terminal device by the means, and the voltage detecting means. Accordingly interface circuit is characterized in that an output means comprising output photo-coupler that outputs the detection result to the terminal network controller when the voltage drop is detected. 5. The interface circuit according to claim 1, wherein the voltage detecting means is a Zener diode. 6. The voltage detecting means comprises a voltage detecting circuit for outputting a drive signal to the output means when a voltage having a value lower than a predetermined reference value is input. The described interface circuit. 7. The voltage detecting means sets the output terminal to the voltage and does not drive the output means when a voltage having a value higher than a predetermined reference value is input from the input terminal, and the voltage detecting means outputs a voltage lower than the reference value. 5. The interface circuit according to claim 1, further comprising a voltage detection circuit that drives the output means by setting the output terminal to a voltage lower than the voltage when a voltage is input.