JPS62163446A - Connecting circuit for modem - Google Patents

Abstract

PURPOSE:To detect a fact that a telephone set has been used, when a MODEM is being connected to a telephone line and to detach automatically the MODEM from the telephone line, by setting the threshold values corresponding to the respective connected states of the MODEM and the telephone set. CONSTITUTION:In a MODEM connecting circuit for connecting or detaching by an opening/closing means 5 to or from telephone lines 2, 2 to which a telephone set 1 has been connected, the first threshold voltage which is lower than a terminal voltage of the telephone lines 2, 2 at the time when the telephone set 1 is not being used and a MODEM 3 is not being connected, and higher than the terminal voltage at the time when the telephone set 1 is being used and the MODEM 3 is not being connected to the telephone line is set by a Zener diode 14. The second threshold value which is lower than the terminal voltage at the time when the telephone set 1 is being used and the MODEM 3 has been connected to the telephone line, and higher than the terminal voltage at the time when the telephone set 1 is being used and the MODEM 3 is being connected is set by a Zener diode 24. When the MODEM 3 is being connected to the telephone line, if the telephone set 1 is used, it is detected that the terminal voltage becomes lower than the second threshold value, and the MODEM is detached automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a connection circuit for a modem serving as an interface for a computer or the like that transmits data through a telephone line.

(Prior Art) Generally, in data transmission using a telephone line, a modem is connected to the telephone line and data is output from a terminal device such as a computer. Since the telephone line is shared with the telephone, in order to give priority to the use of the telephone, when connecting the modem to the telephone line and inputting/outputting data, make sure that the telephone is not in use before transmitting the data. The transmission is configured to take place.

Whether or not this telephone is being used can be determined by the terminal voltage of the telephone line. That is, power for the telephone is supplied from the telephone office in a manner that is superimposed on the telephone line, and when the telephone is used, the terminal voltage decreases due to a voltage drop due to the resistance of the telephone line. Please note that the telephone number is between 50 and 230.
The load resistance is set to Ω, and the telephone line current (loop current) is adjusted to be in the range of 20 to 100 mA.

FIG. 2 shows an example of a conventional modem connection circuit that detects the terminal voltage and connects the modem to the telephone line when the telephone is not in use.

In FIG. 2, telephone line 2.2 to which telephone 1 is connected
is drawn into the modem 3 and connected to the primary side of the line transformer 4 via a relay 5 serving as switching means. The secondary side of the line transformer 4 is connected to a modem circuit 6.

The opening and closing of the relay 5 is controlled by a transistor 9 in response to an opening/closing signal 8 from a control circuit 7 serving as a control means. Well, t-telephone line 2
．． 2 is connected to another relay 10 via a diode bridge 11 in series. This relay 10 is controlled to open and close by a transistor 13 in response to a monitoring signal 12 from a control circuit 7 . The output end of the diode bridge 11 is connected to a Zener diode 14 via a photocoupler 15, and a status signal 16 is applied to the control circuit 7 from the photocoupler 15.

After explaining the operation of the connection circuit of this modem, the terminal voltage between the telephone lines 2 and 2 will be explained. If the telephone 1 is not in use and the modem 3 is not connected, the terminal voltage of the telephone line 2.2 will be approximately 48 V provided by the central office, which is line a in FIG. Also, when the telephone 1 is used or the modem 3 is connected, the telephone line 2,
The terminal voltage decreases due to the voltage drop caused by the resistor 2.2, and the further away from the telephone office the longer the telephone line 2.2 is, the lower the terminal voltage becomes, resulting in lines b and c in FIG. Furthermore, when the telephone 1 is used and the modem 3 is connected, the terminal voltage further decreases to line d in FIG. 3. Note that the loop current of the telephone line 1 is approximately inversely proportional to the length of the telephone line 1.

The operation of the above conventional modem connection circuit will be described below assuming that the loop current is 70 mA.

The terminal voltage is higher than 16V when telephone 1 is used and modem 3 is not connected to telephone lines 2 and 2, and telephone 1
The Zener voltage of the Zener diode 14 is set at a voltage lower than the terminal voltage of 48V when the modem 3 is not in use and the modem 3 is not connected, for example, at a point e in FIG. 3 of 24V. First, when attempting to connect the modem 3 to the telephone line 2.2, the control circuit 7 outputs the monitoring signal 12 and closes the relay 10. Here, when the telephone 1 is not in use, the terminal voltage of the telephone lines 2, 2 rectified by the diode bridge 11 is as high as 48V, causing the Zener diode 14 to break over and the photocoupler 15 to 0.
The high level status signal 16 of (2) is given to the control circuit 7. The control circuit 7 that receives this high-level status signal 16 outputs the open/close signal 8 to close the relay 5, and the modem circuit 6 is connected to the telephone lines 2, 2, and the data is transmitted from the modem circuit 6 to the telephone line. Human output is output through lines 2 and 2. Next, when the control circuit 7 outputs the monitoring signal 12 in an attempt to connect the modem 3 to the telephone line 2.2,
When telephone 1 is in use, diode bridge 11
The terminal voltage rectified in
A low level status signal 16 of 5-5V is applied to the control circuit 7. The control circuit 7 that receives this low level status signal 16 does not output the open/close signal 8 and does not connect the modem 3 to the telephone line 2.2. After a certain period of time has elapsed, the control circuit 7 again outputs the monitoring signal 12 to monitor whether or not the telephone 1 is being used, and if it is detected that the telephone 1 is not being used, the modem 3 is connected to the telephone line. 2. Connect to 2. Therefore, the modem 3 is connected to the telephone line only when the telephone 1 is not in use.

(Problems to be Solved by the Invention) By the way, in the conventional modem connection circuit described above, when the modem 3 is connected to the telephone lines 2, 2, the terminal voltage further decreases when the telephone 1 is used. However, this cannot be detected and the modem 3 cannot be automatically disconnected from the telephone lines 2, 2. Therefore, there is a problem in that it is necessary to manually disconnect the modem 3 in order to use the telephone 1. Particularly when the telephone 1 and the modem 3 are installed in separate locations, it is cumbersome to have to go back and forth between the telephone 1 and the modem 3 for manual operation.

The purpose of the present invention was to solve the above-mentioned problems with the conventional modem connection circuit, and the present invention has been made to automatically disconnect the modem when the telephone is used while the modem is connected to the telephone line. Its purpose is to provide modem connection circuits.

(Means for Solving the Problems) In order to achieve the above object, the modem connection circuit of the present invention connects or disconnects the modem to or from the telephone line connected to the telephone by means of a switching means.
lower than the terminal voltage of the telephone line when the telephone is not in use and the modem is not connected to the telephone line; and lower than the terminal voltage when the telephone is in use and the modem is not connected to the telephone line. a first threshold that is high and lower than any terminal voltage when the telephone is used and the modem is connected to the telephone line; When the terminal voltage is higher than the second
and when attempting to connect the modem to the telephone line, the control means closes the opening/closing means only when the terminal voltage of the telephone line is higher than the first threshold value. connecting the modem to the telephone line;
The control means is configured to open the switching means when the terminal voltage becomes lower than the second threshold.

(Operation) Lower than the terminal voltage of the telephone line when the telephone is not in use and the modem is not connected to the telephone line, and higher than the terminal voltage when the telephone is in use and the modem is not connected to the telephone line. a first threshold and less than any terminal voltage when the telephone is in use or a modem is connected to the telephone line, and less than the terminal voltage when the telephone is in use and the modem is connected to the telephone line; I have set a second threshold that is also high, so that when the phone is used while the modem is connected to the telephone line, it detects that the terminal voltage is lower than the second threshold. The modem can be automatically disconnected from the telephone line by opening the opening/closing means. Therefore, priority is given to using the telephone regardless of whether a modem is connected to the telephone line.

(Description of Examples) Hereinafter, examples according to the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram showing an embodiment of a modem connection circuit according to the present invention. In FIG. 1, circuit elements that are the same as those in FIG. 2 are given the same reference numerals and redundant explanations will be omitted.

The differences between FIG. 1 and FIG. 2 are as follows. The output end of the diode bridge +1 is connected to the first Zener diode I4 via the first photo coupler 15, and in parallel via the second Zener diode 24 and the second photo coupler 25. It is connected. A first status signal 16 is supplied from the first photocoupler 15, and a second status signal 26 is supplied from the second photocoupler 25 to the control circuit 7. Furthermore, the Zener voltage of the first Zener diode 14, which is the first threshold, is higher than the terminal voltage when the telephone 1 is in use and the modem 3 is not connected to the telephone line. voltage lower than the terminal voltage of 48V when modem 3 is not connected,
For example, it is set at point e in FIG. 3, which is 24V. The Zener voltage of the second Zener diode 24, which is the second threshold value, is determined when the telephone 1 is used or the modem 3 is
When connected to telephone line 2.2, telephone 1 is used and modem 3 is connected to telephone line 2.2.
voltage higher than the terminal voltage when connected to, for example, I
Set at point f in FIG. 3 of OV.

In this configuration, when the control circuit 7 outputs the monitoring signal 12 and closes the relay 10 in order to connect the modem 3 to the telephone line 2.2 when the telephone 1 is not in use, the terminal voltage becomes Since the voltage is as high as 48V, both the first Zener diode 14 and the second Zener diode 24 are broken over, and the first photo coupler 15
A first status signal 16 and a second status signal 26 at a high level of oV are supplied to the control circuit 7 from the second photocoupler 25 and the second photocoupler 25 . The control circuit 7 that receives the first and second status signals 16 and 26 outputs the open/close signal 8 to close the relay 5, and the modem circuit 6 is connected to the telephone lines 2 and 2, and the modem circuit 6 is connected to the telephone lines 2 and 2. Data is input and output through telephone lines 2,2. When the modem 3 is connected to the telephone line 2.2 in this manner, the terminal voltage drops to 14V, and the first status signal 16 is inverted to a low level of -5V and is applied to the control circuit 7. When the telephone 1 is used with the modem 3 connected to the telephone line 2.2, the terminal voltage further drops to 5V, and the second Zener diode 25 does not break over, and the second status signal 26 becomes The voltage is inverted to a low level of -5V and applied to the control circuit 7. The control circuit 7 outputs an open/close signal 8 when the second status signal 26 is inverted to low level.
The modem circuit 6 is automatically disconnected from the telephone lines 2 and 2 by cutting off the output of the telephone 1 and opening the relay 5, so that the telephone 1 can be used preferentially.

If the telephone 1 is in use when the modem 3 is connected to the telephone lines 2, 2 and the monitoring signal 12 is output, the terminal voltage is approximately 16V, and the first status signal 1
6 is low level and the second status signal 26 is high level and is given to the control circuit 7, and the control circuit sends it to the telephone 1.
is determined to be in use, the open/close signal 8 is not output, the relay 5 remains open, and the modem 3 is not connected.

The control circuit 7 repeatedly outputs the monitoring signal I2 after a certain period of time to monitor whether the telephone 1 is being used or not, and when it is detected that the telephone 1 is not being used, the modem 3
immediately connect to telephone line 2.2. In addition, if the modem 3 is disconnected from the telephone line 2.2 before data output is completed because the telephone 1 is used while the modem 3 is connected, the control circuit 7 repeatedly sends a message after a certain period of time. The monitoring signal 12 is output to monitor whether or not the telephone 1 is being used. When it is detected that the telephone 1 is not being used, the modem 3 is immediately connected to the telephone line 2.2 and the data is transferred. Continue human output.

Therefore, regardless of whether modem 3 is connected to telephone lines 2 or 2, telephone 1 can be used preferentially.
This eliminates the trouble of having to manually disconnect the modem 3 in order to use the telephone 1 while the modem 3 is connected, as in the conventional modem connection circuit shown in FIG.

(Effects of the Invention) As explained above, according to the modem connection circuit of the present invention, the terminal voltage of the telephone line is lower than the terminal voltage of the telephone line when the telephone is not in use and the modem is not connected to the telephone line. a first threshold that is higher than the terminal voltage when the telephone is used and the modem is not connected to the telephone line, and lower than either the terminal voltage when the telephone is used or the modem is connected to the telephone line; and a second threshold that is higher than the terminal voltage when the phone is in use and the modem is connected to the phone line, so that when the phone is used while the modem is connected to the phone line, , the modem can be automatically disconnected from the telephone line by detecting that the terminal voltage becomes lower than the second threshold and opening the switching means. Therefore, an excellent effect is achieved in that the use of the telephone is prioritized regardless of whether or not a modem is connected to the telephone line.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a modem connection circuit of the present invention, FIG. 2 is a circuit diagram showing an example of a conventional modem connection circuit, and FIG. 3 is a circuit diagram showing an example of a connection circuit of a conventional modem. 2 is a graph showing the relationship between terminal voltage and loop current (length of telephone line). 1: Telephone, 2: Telephone line, 3: Modem, 5: Relay,
6: Modem circuit, 7: Control circuit, 14: First Zener diode, 15: First photo coupler, 16: First status No. 43, 24: Second Zener diode, 25: Second photo coupler , 26: second status signal.

Claims (1)

[Claims] In a modem connection circuit that connects or disconnects a modem to a telephone line to which a telephone is connected by a switching means, the terminal voltage of the telephone line when the telephone is not in use and the modem is not connected to the telephone line. a first threshold that is lower than a terminal voltage when the telephone is in use and the modem is not connected to the telephone line; and when the telephone is in use or the modem is connected to the telephone line. and a second threshold value lower than the terminal voltage when the telephone is used and higher than the terminal voltage when the modem is connected to the telephone line, and attempting to connect the modem to the telephone line. When the terminal voltage of the telephone line is higher than the first threshold, the control means closes the opening/closing means to connect the modem to the telephone line, and the terminal voltage is higher than the second threshold. A connection circuit for a modem, characterized in that the control means is configured to open the opening/closing means when the value becomes lower than a threshold value.