JPH0748780B2 - Incoming signal detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is applicable to telephone lines and PBX (private branch exchange).
The present invention relates to an incoming signal detection circuit used for data communication using the.

[Prior Art] A conventional circuit of this type is shown in FIG. FIG. 3 is a block diagram showing the configuration of a conventional incoming signal detection circuit. In the figure, (1) is a telephone for voice communication (hereinafter, simply referred to as a telephone), and (2) is a telephone line connected to the telephone (1). Relay A to do. (3) is a relay B for connecting the telephone line to the modem side. (4) is a transformer that electrically separates the telephone line from the direct current. (5) is a modem which performs mutual conversion between a digital signal from a CPU (not shown) and an analog signal from a telephone line.
(6) is a photocoupler for detecting the call signal CI, and (7) is a filter for extracting the call signal.

Further, FIG. 2 is a time chart showing various signal waveforms of the conventional apparatus shown in FIG. 3 and the apparatus according to the present invention described later.

Next, the operation of the conventional device shown in FIG. 3 will be described. When there is an incoming call, that is, there is a call from the calling side, if this telephone line is not busy, as shown in Fig. 2 (A).
Call signal modulated at 400Hz / 16Hz is ON for 1 second, OFF for 2 seconds
It is sent to the telephone line as an intermittent signal at intervals of.
On the called side, when the relay A (2) is in the "closed" state, the telephone (1) receives the calling signal and makes a ringing tone. On the called side, the call signal is extracted by the filter (7), the photodiode of the photo coupler (6) is caused to emit light by the extracted signal, and the photo coupler (6) causes the photodiode to emit light. , ▲ ▼ signal, which is an intermittent incoming signal similar to the call signal as shown in Fig. 2 (B), is turned on for 1 second and turned off for 2 seconds.
It sends to the CPU at intervals to let the computer know that there is an incoming call. The CPU measures the ▲ ▼ signal over time, and when the number of calls (that is, the number of times the ▲ ▼ signal is at the "Low" level) reaches a predetermined count, the relay B is closed and the data is transferred. Start receiving.

To measure the number of calls, the CPU generates an interrupt at the falling edge of the ▲ ▼ signal to drive the timer, stops the timer at the rising edge of the ▲ ▼ signal, adds +1 to the counter, and initializes the timer. Again ▲
▼ Measurement is performed by repeating the operation of generating an interrupt when the signal falls.

In this way, the conventional incoming signal detection circuit detects whether a voice call using the telephone (1) or a data communication is made when an incoming call is received on the telephone line.

[Problems to be Solved by the Invention] In the conventional incoming signal detection circuit as described above, an intermittent ▲
▼ Every time the signal falls, an interrupt is generated in the CPU to drive and measure the timer, so the program controls the entire data communication sequentially.
There was a problem that the U was overloaded and the overall processing speed was delayed.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an incoming signal detection circuit that can perform data communication without imposing an excessive load on the CPU and without delaying the processing speed.

[Means for Solving the Problem] The incoming signal detecting circuit according to the present invention sends a signal of a constant level to the CPU until the calling signal disappears when there is an incoming call on the telephone line and the calling signal is sent. I chose

[Operation] According to the present invention, when an incoming call is received on the telephone line and the call signal is transmitted, a constant level signal is transmitted until the call signal disappears, so that only one interrupt is generated to the CPU. It is possible to detect whether the call is a voice call using a telephone or data communication.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an incoming signal detection circuit according to the present invention. In the figure, the same reference numerals as those in FIG. 3 indicate the same or corresponding parts, and (8) is an incoming detection circuit, which is extracted by a filter (7). The photo coupler (6) is driven based on the calling signal. Reference numeral (9) is a comparator A (referred to as a first comparator), which performs waveform leveling on the output of the photocoupler (6) and then performs level conversion.

Also, (C) is a capacitor, (RA) is a capacitor (C).
To discharge the capacitor, (RB) is a resistor for charging the capacitor (C), (11) is a comparator B (referred to as a second comparator), and (R1) and (R2) are respectively the comparator B (11). ), The resistance that determines the reference voltage value,
(R3) resistance to impart a hysteresis characteristic to the comparator _{B (11), (L 1} , L 2) represents the telephone line from the exchange.

Next, the operation of the circuit shown in FIG. 1 will be described. When there is an incoming call, that is, a call from the calling side, FIG. 2 (A)
The call signal modulated by 400Hz / 16Hz shown in is sent to the telephone line as an intermittent signal. The call signal is extracted by the filter (7) and sent to the incoming call detection circuit (8). In the incoming call detection circuit (8), 1 second of this call signal
The light emitting diode of the photocoupler (6) is made to intermittently emit light based on the ON / OFF interval of 2 seconds, and a signal () in FIG. 2B obtains a signal as the output of the photocoupler (6). As shown in FIG. 2, the signal output from the photocoupler (6) is a signal synchronized with the calling signal (A) modulated at 400 Hz / 16 Hz. The comparator A (9) compares this signal with the reference voltage Vref, performs waveform shaping and level conversion, and charges and discharges the capacitor (C) with the level-converted rectangular wave. That is, when the ▲ ▼ signal is at "Low" level, the electric charge stored in the capacitor (C) is discharged through the resistor (RA), and when the ▲ ▼ signal becomes "High" level, the capacitor is now passed through the resistor (RB). (C) is charged. Therefore, the waveform of the signal S ₁ input to the comparator B (11) is as shown in FIG. 2 (C). Also, this signal S ₁
Is compared with the reference voltage S ₂ by the resistors (R1) and (R2) by the comparator B (11) and fed back through the resistor (R3) to obtain the signal CI shown in FIG. 2 (D). The signal CI obtained as the output of the comparator B (11) is the second
Even if the call signal shown in FIG. 7A is intermittent, it is a signal that holds the output of a constant level (that is, logic "1") while the call signal is being sent. In all other cases, the logical value is "0". In this specification, S ₂ is tentatively referred to as the first voltage value.
The lowest value of S ₁ is tentatively called the second voltage value.

Further, the resistance (RA) has a resistance value so that the capacitor (C) can discharge from the vicinity of the first voltage value to the vicinity of the second voltage value during the first ON state of the calling signal shown in FIG. 2 (A). The resistance value of the resistor (RB) is set so that it does not exceed the reference voltage S ₂ when the call signal is in the OFF state.

In the above embodiment, the constants of the capacitor and the resistance are set for the call signal being ON for 1 second and OFF for 2 seconds, but the same applies to other call signals only by changing the constants. It can be carried out. In the above embodiment, for example, a comparator is used as a circuit for level shifting the output of a rectangular wave pulse, but an operational amplifier or the like can be used, and the present invention is not limited to the circuit shown in the embodiment. Needless to say.

[Effects of the Invention] As described above, according to the present invention, when an incoming call is received on a telephone line and a calling signal is sent, a constant level signal is sent until the calling signal disappears, thereby interrupting the CPU once. It is possible to detect whether the call is a voice call using a telephone or data communication by simply generating a call, so that it is possible to avoid the delay of the entire data communication process due to the increase of the CPU load due to excessive interrupts. effective.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an incoming signal detection circuit according to the present invention, FIG. 2 is a time chart showing various signal waveforms, and FIG. 3 is a block diagram showing the configuration of a conventional device. (4) transformer, (5) modem, (6) photocoupler, (7) filter, (8) incoming detection circuit, (9)
Is a comparator A, (C) is a capacitor, (RA), (R
B) is the resistance, (11) is the comparator B, (R
1), (R2) and (R3) are resistors. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A circuit for generating an intermittent rectangular wave pulse from an intermittent call signal from a telephone line, a circuit for level shifting the output of the generated rectangular wave pulse, and an output from the level shifting circuit. A charging / discharging circuit that outputs a voltage value within a preset range during charging and discharging and generation of a rectangular wave pulse, and a comparison circuit that compares the output from this charging / discharging circuit with a reference value and outputs a signal An incoming signal detection circuit, characterized in that a constant level signal output is always obtained from the comparison circuit during reception of a calling signal.