JP2654039B2 - Interface circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial application field) The present invention collects information such as power, gas, water, and security by using a subscriber telephone line and transmits data to a distant place. The present invention relates to an isolation method for a device that performs the operation.

(Prior art) When collecting usage data and security information of power, gas, water, etc., and transmitting the collected data to a distant location using a subscriber telephone line, noise and lightning from the subscriber telephone line to the terminal device In order to prevent the intrusion of surges and to prevent the current from flowing out of the subscriber telephone line due to a short circuit accident in the terminal equipment, the terminal equipment and the network controller (hereinafter referred to as NCU)
) Is required.

A conventional 4-wire interface circuit is configured as shown in FIG.

In this circuit, the transistor 22 of the terminal device 2A and the transistor 26 of the NCU 2B are both OFF in non-communication,
The diodes of the respective photocouplers 24 and 28 do not emit light, and no current flows through the connection lines.

Therefore, the reception level A.IN of the terminal device 2A and the reception level B.IN of the NCU 2B are both at the "H" level.

When starting communication from the terminal device 2A, the transistor 22 is turned on to supply a current to the diode of the photocoupler 24 to emit light. The resistor 21 is a limiting resistor for this current. The transistor of the photocoupler 24 receives the light of the diode and enters the ON state, the reception level B · IN becomes the “L” level, and the NCU 2B starts the communication operation. The resistor 25 is a pull-up resistor and keeps the reception level B.IN at the time of non-communication at 'H'.

When starting communication from NCU2B, use transistor 26
Is turned on, the diode of the photocoupler 28 emits light, and the reception level A · IN of the terminal device 2A is set to “L”, whereby the terminal device 2A starts a communication operation. The resistor 27 is a current limiting resistor for the diode of the photocoupler 28, and the resistor 23 is a pull-up resistor that keeps A.IN at "H" during non-communication.

As described above, in this circuit, the terminal device 2A or the NCU 2B
It starts from both. After both are in communication, when sending data from the terminal device 2A to the NCU 2B, the transistor 22 is turned ON / OFF to change B / IN to 'L'H', and the terminal device 2A When sending data to
The communication is performed by turning on / off the transistor 26 and changing A / IN to "L" H.

However, this method requires four signal lines, which increases construction costs, equipment costs, cable costs, and the like.

To eliminate this drawback, a two-wire interface circuit having two signal lines as shown in FIG. 3 has been considered.

The two-wire interface circuit includes, in the terminal device 3A, a power terminal to which a power signal of a predetermined voltage is supplied;
The collector of the transmission control transistor 32 whose emitter is grounded is connected via a connection line, and a network control device is connected between the power supply terminal and the collector of the transmission control transistor 32.
On the 3B side, the receiving photocoupler 34 and the transmitting photocoupler 38 are inserted and connected.

A power terminal provided in the terminal device 3A is connected in series to the connection line via a current limiting resistor 31,
On the side of the terminal device 3A, the data transmitted from the network control device 3B is extracted by extracting a change in the power supply voltage obtained from the power supply terminal via the current control resistor 31 ( A ・ IN).

The receiving photocoupler 34 is formed by a photodiode that emits light in a conductive state, and a phototransistor with a grounded emitter that receives light generated by the light emission of the photodiode and forms an electric signal in accordance with the light. I have.

Similarly, the transmitting photocoupler 38 is formed by a photodiode that emits light in a conductive state, and a phototransistor that receives light formed by the light emission of the photodiode and forms an electric signal corresponding to the light. I have.

The photodiode of the receiving photocoupler has an anode connected to the current limiting resistor 31, and a cathode connected to the collector of the phototransistor of the transmitting photocoupler. The phototransistor of the receiving photocoupler 34 has a collector connected to a power supply terminal to which a power supply signal of a predetermined voltage is supplied.
Connected through. In the network control device 3B, a change in the power supply signal supplied from the power supply terminal is taken out through a connection point between the collector of the phototransistor and the pull-up resistor 35, so that transmission from the terminal device 3A side is performed. (B)
・ IN).

On the other hand, the emitter of the phototransistor of the transmission photocoupler 38 is connected to the collector of the transmission control transistor 32 on the terminal device 3A side via the connection line. The anode of the photodiode of the transmitting photocoupler 38 is connected via a current limiting resistor 37 to a power supply terminal to which a power supply signal of a predetermined voltage is supplied. The cathode of this photodiode is connected to the collector of the transmission control transistor 36 whose emitter is grounded.

In this circuit, during non-communication, the transistor 32 of the terminal device 3A is turned on and the transistor 36 of the NCU 3B is turned off so that no current flows through the connection line. Therefore, the reception level A of the terminal device 3A
The reception levels B and IN of IN and NCU 3B are both at the “H” level by pull-up resistors 31 and 35.

In this state, turn on the transistor 36 and turn on the photocoupler.
When the diode 38 emits light, the transistor 32 of the terminal device 3A is in the ON state and is on standby, so current flows through the connection line,
The NCU 3B starts up the terminal device 3A. Where A · IN
Becomes 'L', and the terminal device 3A starts the communication operation. NCU3
When data is transmitted from B to the terminal device 3A, the transistor 36 is turned ON / OFF while the transistor 32 is ON, and the A / IN level is changed to "L" H. To transmit data from the terminal device 3A to the NCU 3B, the transistor 3
The transistor 32 is turned ON / OFF while the signal 6 is kept ON, and the B / IN level is changed to “L” or “H” via the photocoupler.

However, in this method, the transistor 36 is turned off during non-communication.
F, it is not possible to activate communication from the terminal device 3A to the NCU 3B.

When the transistor 36 is turned on and the transistor 32 is turned off in the non-communication state, the terminal device 3A is activated by turning on the transistor 32. On the contrary, the NCU 3B is not activated.

Further, in this method, the diode of the photocoupler 34 is inserted in series to the A / IN line,
-Even when IN is at the "L" level, the voltage drop (approximately 1V) of the photocoupler 34 diode will cause a gutter, and the terminal device 3A
'H''L' determination on the side becomes difficult. This is the terminal device 3A
The lower the power supply voltage, the greater the effect.

For example, when the power supply voltage is 5V, 'H' is 5V and 'L' is 1V
However, when the power supply voltage is 3V, 'H' becomes 3V'L 'becomes 1V.

(Problems to be Solved by the Invention) The present invention has two connection signal lines, a terminal device side and an NC.
The present invention provides an isolation system in which starting can be performed from either side of the U side and the effect of a voltage drop of a diode of a photocoupler is reduced.

[Structure of the Invention] (Means for Solving the Problems and Their Operation) The present invention provides at least data relating to the detected amount of an object detected by a terminal device via a subscriber telephone line and a network control device. An interface circuit for connecting the terminal device and the network control device of the data collection system to be transmitted to the center device side, in order to solve the above-described problems,
It has the following characteristic means.

That is, the interface circuit according to the present invention is provided on the terminal device side, and is provided on the terminal device side with a first changeover switch controlled to be switched to a power terminal side or a ground terminal side, and the first switchover is provided on the terminal device side. The second is controlled to be switched to the power terminal side or the ground terminal side contrary to the switch.
And a communication switch from the network control device to the terminal device, the communication control device being provided on the network control device side so as to be inserted into and connected to a connection line connecting each selection terminal of the first and second changeover switches. A transmission unit that is controlled to be in a non-conductive state at other times. A receiving unit provided in the network control device side in parallel with the transmission unit and controlled to be in a non-conductive state except during communication from the terminal device to the network control device; Means connected between a power supply terminal of one of the first switch and the second switch and a power supply so that data transmitted from the network control device to the terminal device can be extracted by the means. A terminal side output terminal; and a network control output terminal for extracting data transmitted from the terminal device via the receiving means.

Then, at the time of non-conduction, the terminal device switches and controls the first and second changeover switches so that both the transmitting means and the receiving means on the network control device side are non-conductive.

Further, at the time of communication from the network control device to the terminal device, the network control device conducts the transmission means according to the data to be transmitted while the first and second changeover switches remain in the non-communication switching state. By controlling the state or the non-conducting state to vary the data taken out via the terminal output terminal of the terminal device, the terminal device is activated and data is transmitted.

Further, at the time of communication from the terminal device to the network control device,
The terminal device sets the receiving means on the network control device side to a conducting state or a non-conducting state according to data to be transmitted.
1, by controlling the switching of the second changeover switch and changing the data taken out from the output terminal on the network control side via the receiving means, to activate the network control device side and transmit the data. It was done.

Embodiment An embodiment of the present invention will be described below with reference to FIG. 1A is a terminal device, and 1B is an NCU. Reference numerals 11 and 12 are power supply switches, and are actually formed of semiconductor switches.
The switches 11 and 12 are controlled by a control unit built in the terminal device 1A. A-IN is a terminal device connected to the switch 12.
When communication data is input to the terminal device 1A, the communication data is input to a control unit built in the terminal device 1A. A pull-up resistor 13 is connected to A.IN, and is connected above the switch 12.

14 is a receiving photocoupler provided on the NCU1B side,
The cathode side of the diode is connected to the switch 12 via one signal line, and the anode side is connected to the switch 11 via the other signal line via the power supply limiting resistor 19. The emitter side of the transistor is connected to the ground level of NCU1B,
The collector side is connected to the pull-up resistor 15 and the input B · IN of the control unit built in the NCU.

Reference numeral 18 denotes a transmitting photocoupler provided on the NCU 1B side.The collector side of the transistor is connected to the switch 12 similarly through the same signal line as the cathode side of the diode of the photocoupler 14 is connected, and the emitter side is connected to a resistor. Similarly, the switch 11 is connected to the switch 11 through the same signal line to which the switch 19 is connected. The anode side of the diode is connected to the power supply of NCU1B through a power supply limiting resistor 17, and the cathode side is connected to the ground level of NCU1B through a limiting transistor 16.

The base of the control transistor 16 is connected to the output B / OUT of the control unit built in the NCU.

Next, the operation of the embodiment configured as described above will be described.

In the normal state (non-communication), the switch 11 of the terminal device 1A
To the ground level side of the terminal device 1A, and switch 12
Is connected to the power supply side of the terminal device 1A through the pull-up resistor 13. In this state, a voltage is applied to the diode of the photocoupler 14 in the reverse direction. Hand photo coupler
Although a voltage is applied to the transistor 18 in the forward direction, the diode of the photocoupler 18 does not emit light because the transistor 16 is in the OFF state, and the transistor of the photocoupler 18 is in the OFF state. Therefore, no current flows through the connection signal line.

When starting communication from the NCU 1B to the terminal device 1A, N
The CU 1B turns on the transistor 16 to supply a current to the diode of the photocoupler 18 to emit light. Then, the transistor of the photocoupler 18 receives the light of the diode, turns on, and allows a current to flow through the connection signal line. Terminal device 1A
When the current flows through the connection signal line, the level of A-IN becomes "L" (a value determined by the resistance division of the pull-up resistor 13, the connection signal line resistance, and the on-resistance of the photocoupler 18). Receiving the change as a "terminal device activation signal",
The communication state is established.

When starting communication from the terminal device 1A to the NCU,
The terminal device 1A connects the switch 11 to the power supply side of the terminal device 1A, and connects the switch 12 to the ground side of the terminal device 1A.
Then, since the voltage applied to the connection signal line is reversed, the diode of the photocoupler 14 becomes a forward voltage, and a current flows to emit light. When the transistor of the photocoupler 14 receives this light, it is turned on, and B.IN is set to the "L" level (a level determined by the resistance division ratio of the full-up resistor 15 and the on-resistance of the transistor of the photocoupler 14). NCU 1B receives this change as an “NCU activation signal” and enters a communication state.

In the communication state, transmission from the terminal device 1A is performed by a switch.
12 is connected to the ground side, the current flowing through the connection signal line is controlled by switching the switch 11, and the photocoupler 14
Through the control of the level of B.IN. Transmission from the NCU 1B is performed by connecting the switch 11 to the ground side and the switch 12 to the power supply side, controlling the current flowing through the connection signal line via the transistor 16 and the photocoupler 18, and controlling the level of A / IN.

As described above, the effect of the present embodiment of the configuration and operation is that the terminal devices 1A and the NCU 1B are isolated by the photocouplers 14 and 18, so that lightning surge and noise from the subscriber telephone line are transmitted to the terminal via the NCU 1B. Intrusion into the device 1A is prevented. In addition, if the current of the subscribed telephone line is drawn due to a short circuit accident in the terminal device 1A and the exchange connected to the subscribed telephone line determines that the line has been seized (off-hook), the same subscribed telephone as the NCU 1B is used. It is also possible to prevent another device (such as a telephone) connected in parallel to the line from becoming unusable.

Also, the number of connection signal lines between the terminal device 1A and the NCU 1B may be two, and the possibility of erroneous connection is lower than that of the four-wire system, and construction, equipment, and material costs are low.

In addition, by having a function of switching the current direction of the connection signal line, mutual communication is enabled, and at the same time, the terminal device 1A and the NCU 1B
Since communication can be activated by either of these methods, the conventional 2-wire interface circuit can only be used for ventilation activation from the NCU 1B, that is, only for a data collection system that calls the terminal device 1A at the center side (center reception). However, it has become possible to use the data collection system of a method of calling the center from the terminal device 1A (terminal transmission).

In addition, since the number of photocouplers on the current loop formed via the connection signal line is reduced as compared with the conventional method, the terminal device 1A
Thus, the voltage of the detection level "L" at the low level becomes low, so that the "L" level can be easily detected even if the "H" level is lowered.

[Effects of the Invention] As described above, according to the present invention, the terminal device
The connection signal line between the NCUs is isolated by two lines, the current direction is switched, communication can be started from both the terminal device and the NCU, and the signal voltage can be reduced, so the center termination method using a subscriber telephone line and the terminal transmission method Can provide a safe and inexpensive interface circuit between a NCU and a terminal device even in a data collection system that is used in combination with the NCU.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment according to the present invention, FIG. 2 is a circuit diagram showing a conventional 4-wire interface circuit, and FIG. 3 is a circuit diagram showing a 2-wire interface circuit according to the prior art. is there. 1A Terminal device, 16 Transmission control transistor 1B Network control device 11, 12 Transmission / reception switch, 18 Photocoupler for transmission 14 Photocoupler for reception

Claims (1)

(57) [Claims] 1. A data collection system for transmitting at least data relating to the detected amount of an object detected by a terminal device to a center device via a subscriber telephone line and a network control device. An interface circuit for connecting to a device, a first switch provided on the terminal device side and controlled to be switched to a power terminal side or a ground terminal side; and a first switch provided on the terminal device side, A second changeover switch that is controlled to switch to a power supply terminal side or a ground terminal side contrary to the switch; and the second changeover switch is inserted and connected to a connection line connecting each selection terminal of the first and second changeover switches. Transmitting means provided on the network control device side and controlled to be in a non-conductive state except during communication from the network control device to the terminal device; Receiving means provided on the network control device side in such a manner as to be in a non-conductive state except during communication from the terminal device to the network control device; and A terminal-side output terminal connected between a power supply terminal and a power supply of any one of the first changeover switch and the second changeover switch so that data transmitted to the terminal device can be extracted; Having a network control side output terminal for taking out the transmitted data via the receiving means, so that when non-communication, both the transmitting means and the receiving means on the network control device side are in a non-conductive state, A terminal device controls the switching of the first and second changeover switches, and performs communication between the first and second changeover switches during communication from the network control device to the terminal device.
While the changeover switch is in the non-communication switching state, the network control device controls the transmitting means to a conductive state or a non-conductive state in accordance with data to be transmitted, via a terminal-side output terminal of the terminal device side. By activating the terminal device side and transmitting data by changing the data to be taken out, the network control device according to the data to be transmitted is transmitted by the terminal device during communication from the terminal device to the network control device. By controlling the first and second changeover switches so that the receiving means on the side becomes conductive or non-conductive, by changing the data taken out from the network control side output terminal via the receiving means, An interface circuit for activating the network control device and transmitting data.