JPH01256255A - Trunk line polarity detection circuit - Google Patents

Abstract

PURPOSE:To decrease the detecting time of the polarity of a trunk line, to attain miniaturization and to reduce the cost by constituting a trunk line circuit by electronic parts such as a light emitting element, a light receiving element and a transistor(TR) and detecting the potential of a terminal part so as to detect the polarity of the trunk line. CONSTITUTION:A current is supplied from an I/O port 1 to a light emitting diode 4 in the detection of polarity. With the light emitting diode 4 lighted, a potential difference is produced across a light receiving element 3 by the optical signal therefrom. The potential difference causes a bipolar TR 2 to be turned on, and with a level of a trunk line L1 higher (lower) than the level of a trunk line L2, an input voltage level of a logic element 7 whose one terminal is connected between the 1st and 2nd resistors 5, 6 connected respectively to the trunk lines L1, L2 becomes lower (higher). Whether or not the trunk lines L1, L2 are busy is detected by the level change and a trunk line polarity signal applied to the I/O port 1 is inputted through the logic element 7. Thus, the detection time is reduced and the constitution is made small.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a station line polarity detection circuit for wired communication, and particularly to a station line polarity detection circuit that detects whether or not a station line is being used by detecting the potential of the station line. Regarding a polarity detection circuit.

[Conventional technology]

Conventionally, this type of station line polarity detection has been performed using an electromagnetic relay or the like.

FIG. 3 is a polarity detection circuit diagram for explaining an example of such a conventional technique.

As shown in FIG. 3, in such a polarity detection circuit, I
By passing a command signal from the /O port 11 to the coil of the detection relay 12, the contact 13 of the detection relay 12 is closed. Therefore, when the potential of L1 of the two station lines is higher than the potential of L2, the light emitting diode 14 lights up, and in the opposite case, it does not light up. In this way, since the light receiving element 15 is activated by the optical signal from the light emitting diode 14, the I10 port 11 determines the polarity by inverting this signal through the logic element 17 such as an inverter. Note that 16 represents a resistor connected between the station lines.

[Problem to be solved by the invention]

The conventional office line polarity detection circuit described above uses a detection relay and an optical coupler consisting of a light emitting diode and a light receiving element, so the detection time is long, at least 2 milliseconds, and the terminal equipment for wired communication can be made smaller. This has the disadvantage of being a hindrance and high cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a station line polarity detection circuit that can shorten the detection time of these station line polarities, and realize miniaturization and cost reduction.

[Means to solve the problem]

The office line polarity detection circuit of the present invention includes a light emitting element that is turned on in response to an electrical signal for detecting the polarity of a telephone line, a light receiving element that receives an optical signal from the light emitting element and outputs an electrical signal, and a light receiving element that outputs an electrical signal in response to an optical signal from the light emitting element. A transistor with two electrodes connected to each end, first and second resistors connected to the telephone line, and a binary state of on or off depending on the potential between the first and second resistors. A logic element that takes
and an I10 port that determines whether or not it is possible to access the exchange via the central office line based on the output of the logic element.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a polarity detection circuit diagram for explaining a first embodiment of the present invention.

As shown in FIG.
The O port 1 supplies current to a light emitting element (hereinafter referred to as a light emitting diode) 4 when detecting polarity based on a command from a microcomputer (not shown). When this light emitting diode 4 lights up, the light receiving element 3 is
A potential difference occurs between both ends of the . This potential difference turns on the bipolar transistor 2, and the station line L1 changes to the station line L2.
When the potential is higher than , the input voltage level of the logic element 7 whose one end is connected between the first and second resistors 5 and 6 connected to the central line L2 becomes low. Also, conversely, the central line L
1 is lower in potential than the station line L2, the input voltage level of the logic element 7 is at the same level as the station line L2 and becomes higher. Based on this level change, it is possible to detect whether or not the office lines L1 and L2 are being used, and input the office line polarity signal applied to the I/O port 1 through the logic element 7. Therefore, a wired communication terminal device incorporating the present polarity detection circuit can determine whether or not it can access the exchange via the central office line.

FIG. 2 is a polarity detection circuit diagram for explaining a second embodiment of the present invention.

As shown in FIG. 2, this embodiment uses a field effect transistor 8 in place of the bipolar transistor 2 in the first embodiment. This MOSFET8
It has the advantage that it can be driven with less power, has a short operating time, and has a sufficient blocking voltage, so it does not cause trouble even with high surge voltages applied to the central office line. still,
Regarding other circuit elements, those having the same numbers as those in the first embodiment shown in FIG. 1 are the same circuit elements, and explanations of their operations will be omitted.

〔Effect of the invention〕

As explained above, the station line polarity detection circuit of the present invention consists of a station line circuit composed of electronic parts such as a light emitting element, a light receiving element, and a transistor, and detects the station line polarity by detecting the potential of the terminal part. It is. Therefore, according to the station line polarity detection circuit of the present invention, (1) the number of elements can be reduced due to the combination of an optical coupler and a transistor;

(2) Since a combination of solid-state elements can be integrated on one substrate, the size can be reduced.

(3) Since it is a combination of solid-state elements, the detection time is less than 1 millisecond, which is less than half that of conventional circuits.

Furthermore, when a field effect transistor is used instead of a bipolar transistor, a high breakdown voltage (600 VAC or higher) can be obtained despite the miniaturization.

There are various effects.

[Brief explanation of the drawing]

Fig. 1 is a polarity detection circuit diagram for explaining the first embodiment of the present invention, Fig. 2 is a polarity detection circuit diagram for explaining the second embodiment of the invention, and Fig. 3 is a polarity detection circuit diagram for explaining the second embodiment of the invention. FIG. 2 is a polarity detection circuit diagram for explaining an example. 1...I10 port, 2...Transistor, 3...
- Light receiving element, 4... Light emitting element, 5... First resistor, 6... Second resistor, 7... Logic element, 8...
Field effect transistor. Agent: Susumu Uchihara, Patent Attorney Figure 1, Figure 2 and Figure 3

Claims (1)

[Claims] A light emitting element that lights up in response to an electrical signal for detecting the polarity of a telephone line, a light receiving element that outputs an electrical signal in response to the optical signal from the light emitting element, and two electrodes connected to each end of the light receiving element. a transistor, first and second resistors connected to the telephone line, a logic element that takes on or off depending on a potential between the first and second resistors, and the logic element. I determines whether or not the exchange can be accessed via the central office line based on the output of
/O port.