JPH0561833B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a terminal device in a data transmission system using a general subscriber telephone line, and more specifically, to a terminal device in a data transmission system that uses a general subscriber telephone line, in addition to a telephone. The present invention relates to a data terminal device that is designed so that communication of one device does not trigger activation of another device when the device is shared for data transmission.

<Background> In recent years, automatic meter reading for reading the usage of water, gas, electricity, etc., and monitoring of various electric power equipment, etc.
General subscriber telephone lines (hereinafter referred to as telephone lines) are used as a method to easily collect small amounts of data scattered over a wide area, such as surveys of vending machine usage, by sequentially activating slave stations from the master station. The data transmission method using this method is the most promising and is attracting attention. When transmitting data using such telephone lines, it is no exaggeration to say that the terminal system determines the cost (price) of the system, and in order to reduce the cost of the terminal system, it is necessary to use commercial power as the operating power source. It is no longer a good idea to use the power supply from the exchange, and the central office power source from the exchange is now being used as is.

Furthermore, recently, public facsimile machines that use regular subscriber telephone lines have become popular for home use, and are designed to automatically receive calls using special signals from special facsimile communication networks.

However, when two terminal devices with automatic call receiving functions, such as an automatic meter reading system and a public facsimile system, are connected together to a single telephone line, the data transmission signal of one terminal device can cause the other terminal to receive a call. There is a possibility that the device may be difficult to start.
For example, 16 from the exchange side to one terminal device.
When the activation condition is only a special single frequency signal other than Hz (or pulse), the single frequency component in the spectrum due to the frequency modulation (deviation, FS) signal for data communication of the other terminal device It is possible that the device may start up incorrectly.

<Object of the Invention> The object of the invention is to ensure that, when two data terminal devices with automatic meter reading and automatic call receiving functions such as public facsimile machines are connected to a single telephone line, they can be connected correctly without affecting each other. The object of the present invention is to provide a data terminal device that can perform a startup operation.

<Summary of the Invention> In the present invention, when two terminal devices each use a special single frequency signal as an activation condition, the terminal device located higher than the telephone line receives at least the data transmission signal during its own data transmission. By inserting a circuit that blocks this into the communication path to the lower-level terminal equipment, we prevent the lower-level terminal equipment from erroneous activation.In addition, when the lower-level equipment with a higher priority is operating, it detects its DC loop and activates itself. prevent accidental startup. In this case, the terminal device using the local power source is placed at the highest level with respect to the telephone line, and the lower the position, the higher the priority is usually given.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Data terminal device A In the figure, 1 is a terminal device A according to the present invention, and 40 in the terminal device A is a portion including a signal blocking circuit and an off-hook detection circuit, which are the key points of the present invention.
101 is the other terminal device B, and 201 is a telephone. It is assumed that the terminal device A1 operates using the local power source, and the terminal device B101 operates using the commercial power source.

In the terminal device 1, the two diodes 2 are turned on when the polarity of the telephone lines 11 and 12 becomes opposite to that during telephone standby, and the diodes 2 of the AC signal coupling transformer 3 are turned on.
A capacitor 5 is inserted into the center tap on the next side, and connection lines 3a and 3b to the power supply circuit 6 are taken out from this. A single frequency receiving circuit 7 is connected to the secondary side of the transformer 3, and a transmission circuit 9 is also connected via a switch circuit 8. The transmission circuit 9 includes a modulation/demodulation section for data communication, a data processing section, and an interface section with external equipment, and is connected to a connection line 16 with the outside.

In the section 40, a relay contact 33 is a contact of a relay 31 which is controlled to break when the terminal device A1 enters a data communication mode, and a contact 34 is similarly controlled to make when the terminal device A1 enters a data communication mode. The off-hook detection circuit 10 that detects that the lower terminal device B 101 or the telephone 201 has made a call, that is, has formed a DC loop, is the contact 34 of the relay 32 and the charging capacitor 35.
and is connected between the terminals 21 and 22 through a resistor 36. After the off-hook detection circuit 10 detects this,
The switch circuit 8 is turned off by the control line 14. Further, the connection line 13 is a line for controlling the switch circuit 8 when a single frequency signal is received by the reception circuit 7, and the connection line 15 is a current supply line from the power supply circuit 6 to each part of the terminal device A, and is a line for controlling the switch circuit 8 when a single frequency signal is received by the reception circuit 7. 21, 22
is terminal device A and terminal device B101 or telephone 2
01 connection terminal.

In this terminal device A1, for example, the polarity of the telephone lines 11 and 12 to which the terminal device A1 of the slave station selected by the calling signal from the master station receiving the no-ringing service is connected is inverted by the exchange,
The terminal device A1 is supplied with power by the station power supply,
After that, the terminal device A1 receives a single frequency signal sent from the station and is set to the operating state. It uses local power from telephone lines 11 and 12 and is activated and operated by reverse polarity and single frequency signals. Furthermore, in the data communication mode, first the relay 32 is driven by the control line 13, the relay contact 34 is made, and the capacitor 35 is charged with the potential from the telephone line, and then the relay 32 is driven by the control line 23.
1 and the relay contact 33 breaks. After that, the terminal device sends data, but during data communication
Data transmission signals such as FS signals are sent to lower terminal equipment B,
The relay contact 33 leaks to the telephone 201 side.
This is prevented by the break. When the terminal device B 101 or the telephone 201 forms a DC loop for making a call during data communication, the energy stored in the capacitor 35 flows through the DC loop, the off-hook detection circuit 10 detects the call, and the control line 14 The switch circuit 8 is turned off to stop sending data signals from the terminal device A1 to the telephone lines 11 and 12. When terminal device A1 is not performing data communication, relay contact 33 is closed and contact 3 is closed.
4 is broken, and relay contact 3 is broken even when the terminal device B101 is communicating data or the telephone is talking.
4. The capacitor 35 and resistor 36 maintain a sufficiently high impedance to the telephone line side in terms of alternating current.

Terminal device B Next, in the terminal device B 101, an AC signal coupling transformer 103, a DC blocking capacitor 105 inserted into the primary side of the transformer 103, a single frequency receiving circuit 107 connected to the secondary side of the transformer 103, and A transmission circuit 109 is provided which is connected to the secondary side of the transformer 103 via a switch circuit 108. The transmission circuit 109 includes a modulation/demodulation section and a data processing section for performing data communication. Off-hook detection circuit 110 detects that telephone 201 is in use and turns off switch circuit 108 via connection line 114. When answering an automatic call or making a manual call, a switch 131 for creating a DC termination with a resistor 132 connects the terminal 111,
112, and the switch 131 is controlled by driving a relay 133 via a control line 116 from the transmission circuit 109. A current supply line 115 from the power supply circuit 106 that uses commercial power is connected to the terminal device B1.
Connected to each part of 01. Terminals 121 and 122 are connection terminals of telephone 201. This terminal device B
101 operates using an external commercial power source, and automatically starts and operates in response to a call only when a predetermined single frequency signal is received. This terminal device B101 is, for example, a terminal device for a public facsimile communication network, that is, it has an automatic call receiving function and a manual calling function. When the subscriber lines 11 and 12 are supplemented by a selection signal from the other subscriber, a single frequency signal is sent out from the station as a calling signal. This single frequency signal is 1300Hz, which is different from the single frequency signal used for no-ringing services. When the detection circuit 107 detects this calling signal, it is transmitted to the transmission line 109 via the switch circuit 108.
is connected. At this time, the relay 133 is driven from the control line 116 of the transmission circuit 109, and the relay switch 131 is turned on to create a DC loop, thereby sending a connection completion response signal to the office side. In addition, the calling operation from the terminal device B101 starts the relay 133 by the control signal on the control line 116, sends the calling signal by closing the relay switch 131, and then sends the dial signal of the other party's terminal device to establish the selected connection. It is done.

If we consider normal data communication, a frequency modulation (deviation, FS) signal method is generally used.
This FS signal is a binary frequency modulation signal whose frequency is shifted by logic 1 or 0, and its spectrum is determined by the shift ratio, that is, the ratio of the mark/space frequency shift to the dot frequency. Here, the dot frequency is a frequency determined by the communication speed and the pattern component of logical 1 or 0 (for details, see ``Data Transmission'', translated by Shogo Amari, published by Latisse, etc.). Although the level of such a spectrum varies, it appears as various frequency components depending on the code being communicated, and may transform into a single frequency, which is the activation condition for the terminal device, leading to the terminal device's erroneous activation. .

In this invention, in order to prevent erroneous activation due to the spectrum of the FS signal during data communication, a relay contact 3 is connected to the communication path connected to the lower terminal device B101.
At least a circuit for blocking the data transmission AC signal, such as a band-removal filter or the like, is inserted. Furthermore, the off-hook detection circuits 10 and 110 identify that the lower-level terminal device 101 is in operation and prohibit its own operation, thereby preventing erroneous activation due to data transmission signals of other terminal devices or voice of a telephone, etc. has been established. That is, when telephone 201 starts making a call, both off-hook detection circuits 10 and 110 detect telephone 2 even if either terminal device A or terminal device B is in operation.
01 is detected, and the detection output turns off the switch circuits 8 and 108, respectively, and the transmission circuits 9 and 109 are disconnected from the circuit sending out to the telephone line. Next, if terminal device B starts making a call while telephone 201 is in a dormant state, terminal device A
The off-hook detection circuit 10
detects an off-hook due to a call from terminal device B,
By turning off the switch circuit 8 via the control line 14, the transmission line 9 of the terminal device A is disconnected from the circuit for sending out the data signal to the telephone line, thereby preventing malfunction of the data signal sending operation of the terminal device B. Furthermore, telephone 20
1. When terminal device B is in a dormant state and terminal device A is in operation, the AC signal blocking circuit inserted in the communication path to which terminal device B is connected, that is, the relay contact 33, is connected to the control signal line 23. It is broken by driving the relay 31, and it is possible to prevent the data transmission signal from leaking to the terminal device B and the telephone side. This off-hook detection circuit can also serve as a priority determination circuit that can simultaneously stop the data communication of this terminal device A by a terminal device or telephone with a high priority connected to the next stage or later.

In the description, the terminal device A of the present invention has been described as using a local power source, but the present invention is not limited thereto. Although the AC blocking circuit has been described using relay contacts, any circuit that can block data transmission signals may be used. The off-hook detection circuit is also just one example.
Further, although the AC blocking circuit and the off-hook detection circuit of the present invention are included in the terminal device A, they may have a separate structure. In that case, the principle remains the same even if a battery or the like is used as the operating power source for the relay or the like and as the energy for off-hook detection.

<Effects> As described above, according to the present invention, a multipurpose and highly reliable communication system is realized in which a telephone subscriber line and at least two data terminal devices A and B share a single subscriber telephone line.

[Brief explanation of the drawing]

The figure is a connection and block diagram of a terminal device according to the present invention. 1...Data terminal device, 8,108...Switch circuit turned off by off-hook detection circuit,
9,109...Transmission circuit, 10,110...Off-hook detection circuit, 11,12...Telephone line, 1
01...terminal device, 201...telephone.

Claims (1)

[Claims] 1. A device having first and second terminal devices connected to subscriber telephone lines and selectively set by detection of first and second tone signals from an exchange, wherein the first terminal device is connected to the second terminal device. an off-hook detection circuit for detecting a call from a terminal or a telephone connected to the telephone line and generating an off-hook signal; and supplying a data signal to the telephone line in response to the detection of the first tone signal; a switch circuit for stopping supply of the data transmission signal to the telephone line in response to the off-hook detection signal, and a switch circuit for stopping supply of the data transmission signal to the telephone line in response to the off-hook detection signal; An AC signal blocking circuit for blocking the data transmission AC signal from being supplied to the second terminal device is inserted in series between the second terminal device and the branched connection communication path of the telephone line. and in response to the detection of the first tone signal, one of the telephone set and the second terminal device receives a direct current from the telephone line to form a direct current loop prior to the start of operation. A data terminal device characterized in that a direct current supply means for supplying direct current is connected in parallel to the branched connection communication path.