JPH01253361A - Incoming signal detecting circuit - Google Patents

Abstract

PURPOSE:To avoid the delay of entire data processing due to the increase in load on a CPU caused by excessive interruptions by transmitting continuously signals of a fixed level until no call signal exists any more in case a telephone circuit has an incoming call and the call signals are transmitted. CONSTITUTION:The call signals sent to a telephone circuit as intermittent signals are extracted by a filter 7 and transmitted to an incoming detecting circuit 8. The circuit 8 actuates intermittently a light emitting diode of a photocoupler 6 based on intermittent intervals, i.e., 1-second ON and 2-second OFF of said call signals. Thus the signal, the inverse of CI, of the photocoupler 6 is obtained. This signal is compared with a reference voltage Vref by a comparator A9. Then the comparator A9 performs waveform shaping and level conversion and a capacitor C is charged and discharged by a rectangular wave that undergone level conversion. The signal CI obtained as the output of a comparator 11 holds the output of a fixed level even with the intermittent call signals and as long as these signals are continuously transmitted.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to telephone lines and private
The present invention relates to an incoming signal detection circuit used for data communication using branch exchange.

[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.
1) Relay A connected to. (3> is relay B for connecting the telephone line to the modem side. (4) is a transformer, which electrically separates the direct current from the telephone line. (5) is the modem and the CPU (not shown). Mutual conversion is performed between the digital signal from the telephone line and the analog signal from the telephone line. (6) is a photocoupler for detecting the calling signal CI, and (7) is a filter for extracting the calling signal. be.

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

Next, we will explain the operation of the conventional device shown in Figure 3.3 When there is an incoming call, that is, a call from the calling party, if this telephone line is not busy, the operation as shown in Figure 2 (A) will occur. 4
00Hz/16Hz modulated calling signal for 1 second
N, 0 is sent to the telephone line as an intermittent signal at 2 second OFF intervals. On the called side, relay A (2) is "closed".
state, the telephone (
1) emits a ringing tone. In addition, on the called side, this calling signal is extracted by a filter (7), and the extracted signal causes the photodiode of the photocoupler (6) to emit light. , the CI signal, which is an intermittent incoming signal similar to the calling signal shown in Figure 2 (B), is sent to the CPU at intervals of 1 second ON and 2 seconds OFF to notify the computer that there is an incoming call. ing.

The CPU measures the time of this CI signal, and when the number of calls (that is, the number of times the CI signal is at r Low J level) reaches a predetermined count, it closes relay B and stops receiving data. Start.

To measure the number of calls, the CPU generates an interrupt when the CI signal falls and drives a timer.
The timer is stopped at the rising edge of the C signal, +1 is added to the counter, the timer is initialized, and an interrupt is generated again at the falling edge of the CI signal. This operation is repeated.

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

[Problem to be solved by the invention] In the conventional incoming signal detection circuit as described above, intermittent C
Every time the I signal falls, an interrupt is generated to the CPU and the timer is driven and measured, so the CPU controls the entire data communication sequentially by the program.
There was a problem in that an excessive burden was placed on U, causing a delay in the overall processing speed.

The present invention was made to solve this problem, and an object of the present invention is to provide an incoming signal detection circuit that can perform data communication without placing an excessive burden on the CPU and without slowing down the processing speed.

[Means for Solving the Problems] The incoming signal detection circuit according to the present invention is configured such that when there is an incoming call on a telephone line and a ringing signal is sent, a signal at a constant level is sent to the CPU until the ringing signal disappears. I made it.

[Function] In this invention, when there is an incoming call on the telephone line and a ringing signal is sent, a signal at a constant level is sent until the ringing signal disappears, thereby generating only one interrupt to the CPU. , it becomes possible to detect whether a telephone call is a voice call or a data communication.

[Example code] Embodiments 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 in FIG.
Based on the call signal extracted in 7), the photocoupler (6)
).

(9) is a comparator A (referred to as a first comparator) which performs waveform shaping on the output of the photocoupler (6) and then converts the level.

Also, (C) is a capacitor, (RA) is a capacitor (C
), (RB) is the capacitor (C
), (11) is the comparator B
(referred to as the second comparator), (R1), (R2)
are the resistors that determine the reference voltage value for this comparator B (11), and (R3) is the resistor that determines the reference voltage value for this comparator B (11).
1) Resistance for giving hysteresis characteristics, (Ll
, L2) indicates the telephone line from the exchange.

Next, we will explain the operation of the circuit shown in Figure 1. When there is an incoming call, that is, a call is made from the calling side, the calling signal modulated at 400Hz/16Hz as shown in Figure 2 (A) is intermittent. It is sent as a signal to the telephone line. A filter (7) extracts this calling signal and an incoming call detection circuit (8)
The incoming call detection circuit (8) that sends the call signal to the photocoupler (6) intermittently causes the light emitting diode of the photocoupler (6) to emit light based on the intermittent interval of 1 second ON and 2 seconds OFF of this calling signal. The CI signal shown in FIG. 2(B) is obtained as the output. 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 to 716 Hz.

Comparator A (9) converts this signal to reference voltage Vr.
In comparison with ef, waveform shaping and level conversion are performed, and the level-converted rectangular wave is used to charge and discharge the capacitor (C). In other words, when the signal is r Low level, the capacitor (C) is ) is discharged and the C signal reaches rH1ghJ level, then the capacitor (C) is charged through the resistor (RB). Therefore, the signal S input to comparator B (11)
The waveform of No. 1 is as shown in FIG. 2(C). Further, this signal S is compared with the reference voltage S2 by the resistors (R1) and (R2) by the comparator B (11), and
3) to obtain the signal CI shown in FIG. 2(D). The signal CI obtained as the output of this comparator (11) remains at a constant level (i.e., It is a signal that holds the output of logic "1"), and in other cases, the output is logic "1").
In this specification, S2 is tentatively referred to as a first voltage value, whereas the lowest value of Sl is tentatively referred to as a second voltage value.

The resistance value of the resistor (RA) is set so that the capacitor (C) can be discharged from around the first voltage value to around the second voltage value during the initial ON state period of the calling signal shown in FIG. 2 (A). The resistance value of the resistor (RB) is determined so that the voltage does not rise above the reference voltage 82 when the calling signal is in the OFF state.

In the above embodiment, the call signal is ON for 1 second.

Although the constants of the capacitor and resistor are set for 2 seconds OFF, the same operation can be performed for other call signals by simply changing these constants.

[Effects of the Invention] As explained above, when there is an incoming call on the telephone line and a ringing signal is sent, this invention can interrupt the CPU once by sending a signal at a constant level until the ringing signal disappears. It is possible to detect whether it is a voice call using a telephone or a data communication by simply generating a message, thereby avoiding delays in the entire data communication process due to an increased burden on the CPU due to excessive interrupts. effective.

[Brief explanation of the drawing]

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 call detection circuit, (9)
is comparator A, (C) is capacitor, (RA),
(RB) are respective resistances, (11) are comparator B
, (R1), (R2), and (R3) are resistors, respectively. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] Means for generating intermittent square wave pulses from intermittent ringing signals from a telephone line; a first comparator for level-shifting the output of the square wave pulses; and an output of the first comparator. The charging circuit charges and discharges the capacitor, and the discharging circuit is provided with a resistor having a time constant that discharges the voltage of the capacitor from the first voltage value to the second voltage value during the existence period of the rectangular wave pulse. a capacitor circuit provided with a resistor having a time constant for charging the voltage of the capacitor from the second voltage value to a voltage value lower than the first voltage value during the rest period of the rectangular wave pulse; and a second comparator that outputs a logic "1" signal when the output is a voltage value equal to or higher than the first voltage value, and outputs a logic "0" signal otherwise. Incoming signal detection circuit.