JPS5811153B2 - Confidential communication method for button telephone equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a key telephone device, and more particularly to a confidential telephone system of the key telephone device.

Conventional button telephone devices use cables with a large number of core wires to connect the main device and the telephone.

However, in recent years, systems have become larger and more multifunctional, and materials and labor costs have also increased, leading to an increase in system costs.

Therefore, providing a means for reducing the number of cable core wires is an effective means for reducing costs.

Therefore, as a means of reducing the number of cable core wires, it is common to move the switching of communication paths such as office lines from the current telephone set to the main unit, as is generally used in exchanges.

However, this conventional method has the disadvantage that the main device becomes large and expensive.

Furthermore, the privacy device of the conventional button telephone device is installed inside the telephone, and requires a relay contact to disconnect the communication path to make the conversation confidential.

This is not only disadvantageous in terms of implementation of telephones, but also an obstacle in terms of quality, performance, price, maintenance services, etc.

The present invention eliminates these drawbacks of the prior art and provides a confidential communication system for a key telephone device that can significantly reduce the number of cable cores between the main device and the telephone and realize a low-cost device.

For this reason, the present invention aims to reduce the number of cable cores by using a time division multiplexing method for the control line and communication path of the key telephone device, and integrates the office line secret circuit into the main device so as to directly control the time division path. The above-mentioned drawbacks are solved by mounting the device, making it easier to control with an electronic circuit, and reducing the size.

That is, in order to achieve this object, the present invention provides a key telephone device in which a plurality of key telephones are selectively connected to a plurality of office lines using a main device, a plurality of call lines, and a plurality of control lines. a first pulse generator for generating, in the main device, a clock pulse, a plurality of rows of modulation/demodulation high speed time slot pulses corresponding to the office line, and a plurality of rows of low speed time slot pulses for control signal transmission corresponding to the control line; 1.2, 4, 5, and a plurality of first time division switches 21° connected to the plurality of office lines so as to correspond to each other and controlled by corresponding pulse trains of the plurality of trains of modulation/demodulation high speed time slot pulses. 22, a plurality of second time divisions corresponding to key telephones, each connected to the telephone line so as to correspond to each of the plurality of key telephones, and controlled by corresponding pulse trains of the plurality of trains of modulation/demodulation high speed time slot pulses; a switch 16.20, and a plurality of circular memories 12.13.14 corresponding to button telephones, the output sides of which are connected to the plurality of second time-sharing switches;
a plurality of cyclic memories for writing control outputs transmitted from the corresponding button telephones via the control lines into corresponding ones of the plurality of circulating memories in synchronization with the plurality of rows of low-speed time slot pulses for transmitting control signals; How to write? , 8
, 9, 10° IL40, and a phone compatible device for temporarily blocking the writing operation to the corresponding circulating memory for the time period when the output pulse of any one of the plurality of circulating memories exists. Plural feedback means 218, 400, 216° 217, ...
and a plurality of opening means 211 for temporarily opening the corresponding loops of the plurality of feedback means for the time of the pulse by an output pulse from a corresponding one of the plurality of circulating memories; Each of them includes a second pulse generator 26°27.28 for generating a synchronous time slot pulse that is substantially synchronized with a corresponding one of the plurality of rows of low-speed time slot pulses for transmitting control signals.
and operating means 33, 3 including a plurality of office line telephone keys compatible with the office line.
4, 73, and control output means 31, 3 for taking out the control output from the corresponding button telephone by AND outputting the output of the operating means and the synchronous time slot pulse.
2, 36, one of the central office lines designated by the control output sent by a designation operation of the central office line telephone key in any one of the central telephones is time-divisionally connected to the central telephone. This is a confidential telephone system for a button telephone device, characterized in that it is configured such that a call to a central office can be made while maintaining confidentiality for other key telephones.

Further, gates 251 and 218 are provided between the plurality of circulating memories and the feedback means, and gates 251 and 218 are provided to operate in response to a signal at a predetermined timing and to block the output signal of the plurality of circulating memories, and the plurality of telephones Each of the plurality of telephones is provided with a second operation means such as a deprivation telephone key for connecting the plurality of telephones to the central office line, and the gate is operated by the output of the second pulse generator and the second operation means. , the output of the circular memory may be blocked to allow connection of a plurality of telephones to the same central office line.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the entire key telephone device related to the present invention.
n is a station line, and 100-1 and 100-n are station line circuits provided corresponding to the station lines, each of which is connected to the data highway DH.

200-1...200-m are subscriber circuits corresponding to telephones connected to telephone installations-1, . . . 200-m, respectively.

TMU is 100-1...100-n. 2
This is a common circuit that generates a control signal for controlling 00-1...200-m.

NET in the facility is a telephone communication circuit, and CU is a telephone control circuit.

In order to explain the operation of the present invention in detail below, route circuit diagrams of [100-1→DH→200-1→location, l] in FIG. 1 are shown in FIGS. 2 and 3.

FIG. 2 is a circuit diagram for telephone communication according to the present invention,
1, 27 are counters, 2, 26 are clock pulse generators, 3, 4, 28 are decoders, 5°10 are inverters, 8
, 11. 14, 15, 31 are and gates, ? ,9,1
2.32 is an OR gate, 13 is a shift register, 16,
20, 21° 22 is a time division switch, 17, 23 is a low-pass filter, 19.25 is a transformer, 29 is a telephone communication circuit, 30.36 is a hook switch, 33° 34 is a contact point for the telephone key for selecting a central office line, 35 is a 37°38.39 is a cable, 40 is a flip-flop circuit, ■ indicates the (A) side of the power supply, and E indicates the (→ side) of the power supply.

Further, 100 is an office line circuit, 200 is a subscriber circuit,
A plurality of office line circuits and a plurality of subscriber circuits are connected in parallel through communication buses A and B.

Here, multiple office line circuits connected in parallel are provided, one for each office line, but the gate time slot of the time division switch is set to be different depending on each office line. .

For example, in Fig. 2, this time slot is t,
Another station line is set as t3, the next one is set as t5, and so on.

Here, in order to operate the above circuit, first, the counter and 27 are replaced by the clock pulse generators 2 and 26, respectively.
, and further assume that they are synchronized.

When the user raises the handset and presses the central office line key to make a call to the central office line, contacts 33 and 36 become connected.

As a result, the timing pulse 'Iv9 of the output signal from the decoder 28 driven by the output signal of the counter 27 is transmitted as follows:
A 1400 Å force is applied to the flip flora terminal at the route of .

As a result of the above, a signal has been sent from the telephone to the main device indicating that the central office line cannot be selected.

The sent signal is received by the main device and shifted to shift register 3.
is memorized.

Here, the timing for inputting to the shift register 3 will be explained.

First, the counter is constituted by a plurality of cascaded binary counters, and is driven by a clock pulse train cp which is the output of the clock pulse generator 2.

A time chart of the output C...--CIO of the counter 1 is shown in FIG. 34.

Next, depending on the output of the counter, decoder 3 and decoder 4 are
and their respective outputs t......t
, T......Tn is obtained.

Here, TI...Tn is a signal whose pulse width is the cycle of the output C8° of the counter 1, as shown in FIG.

Also, t□......-tn is a signal whose pulse width is the period of CP, as shown in FIG. 3, and T1...
...compared to the pulse width of Tn...
...The pulse width of tn is sufficiently small.

Furthermore, the signal from the telephone 7...7 and T.
There is a relationship between Tn and Tn as shown in FIG. 3, 2 and 3, and they are synchronized with a certain delay.

FIG. 3 is a diagram showing the timing of data in the case of five office lines, and in the figure, LK1, . . . , LK indicate signals for the office line telephone keys, respectively.

Further, T indicates a unit time in which T1......T is a time slot.

As is clear from this figure, the transmission signal T'9 from the telephone to the main device is delayed by a certain period of time with respect to T9.

This delay is for correcting the synchronization between the counter and the counter 27 by receiving it near the center of the pulse width when the main device receives it.

In FIG. 2, the flip-flop 40 is of a type that outputs an output at the rising edge of the gate pulse C1o.

Therefore, as described above, when the input signal T' is applied here, it is output to the output side of the flip-flop 40 in synchronization with the gate pulse CIO, and is applied to one of the input terminals of the AND gate 11.

The output signal at this time is synchronized with T'to.

Here, C8° is the output of counter 1.

Next, the shift register 13 outputs [output terminal of shift register 13 → AND gate 14 → OR gate 12 →
A feedback loop is formed by the input terminal of the shift register 13, and the shift register 13 is shifted by the clock pulse CP, and the information input here circulates at a constant cycle.
configured to be remembered.

Therefore, in order to input the signal to the shift register 13,
A timing pulse is output from the OR gate 9 by a circuit constituted by an AND gate 8 and an OR gate 7.9, and one of the output signals is applied to an AND gate 14 through an inverter 10 to close it.

The other signal is applied to the AND gate 11 to open it, thereby inputting the signal applied from the flip-flop 40 to the shift register 13 through the OR gate 12.

Here, this input timing is t8 and t2 as described above.
Therefore, the storage location in the shift register 13 is also fixed, and the signal is output at timings 11 and 12 one cycle later.

Here, in order to synchronize the input and output of the shift register 13, the storage capacity of the shift register 13 is set to be the same as steps t1...tn of one cycle of the decoder 3.

As a result of the above, the office line signal input from the telephone is tl
, t2, which is further converted into the timing of C1 by the AND gate 15, so that only tl is utilized and applied to the gate terminals of the time division switches 16 and 20.

Here, C1 is the output of the first stage of counter 1.

As described above, the time division switches 21 and 22 installed in the office line circuit 100 and the time division switches 16 and 20 installed in the subscriber circuit 200 are opened at the same timing, and calls between the office line and the telephone are This is possible with the following route.

That is, the transmission signal from the office line excites the transformer 25,
By its output, [secondary winding 25-2 of transformer 25→
Hybrid 24 → Time division switch 21 → Call bus B →
Time division switch 16 → low pass filter 1γ → hybrid 18 → primary side 19-1 of transformer 19 → earth E]
A communication current flows through the route, excites the transformer 19, and its output is [secondary side (upper) winding 19-2 of the transformer 19→
Cable 38 → Switch 30 → Call circuit 29 → Cable 39 → Secondary side (lower) winding of transformer 19 19-3
→Power supply 35], the communication current flows through the route and is received by the telephone.

In addition, the transmission signal from the telephone energizes the transformer 19 through the same route as described above, and its output causes [the primary winding 19-1 of the transformer 19 → the hybrid 18 → the time division switch 20
→Telephone bus A→Time division switch 22→Filter 23→Hybrid 24→Secondary winding 25-2 of transformer 25→Earth E] A communication current flows through the route, exciting the transformer 25, and the signal is transmitted to the primary of the transformer 25. It is induced in the winding and sent out to the central office line.

Here, the signals on call buses A and B are PAM modulated.

Furthermore, in FIG. 2, only one office line circuit, one subscriber circuit, and one telephone set are shown.

Actually, as shown in FIG. 1, a plurality of them are connected in parallel through communication buses A and B terminals which are part of the data highway DH.

That is, assume that five circuits are connected in parallel to call buses A and B.

At this time, the gate pulse to the gate of the time division switch is 1
1 (for circuit 100), T3. T5. In this case, the OR gate 7 and the AND gate 8 are provided for each office line, and the input signal 11.12 of the OR gate 7 and the input signal TI of the AND gate 8 are set as T7゜T9.
The signals corresponding to O are tl, T2:T in response to the station line circuit gate pulses t1......t, respectively.
3. T4; T5. T6; T7゜1; 11 and TIO
I T'tt t T12 , T13 jT14 are set, and each of these circuits is connected by an OR gate 9 .

In this state, when another office line is selected and a pulse T'1o is received from the telephone, tl
It becomes possible to communicate with the office line circuit to which the gate pulse has been assigned.

As described above, it is possible to talk to any office line by selecting the office line key of the telephone.

Further, in FIG. 2, subscriber circuits are also connected in parallel through call buses A and B, but in this case, the operation is similar to that of circuit 200, and communication with any central office line is possible.

Also, in the above explanation, the time slots of the time division switch are set as tl j T31 T5..., and the storage capacity of the shift register 13 is used twice as much as the required number, and every other bit is This improves the crosstalk characteristics during channel switching.

However, in order to save storage capacity, it is possible to stop using every other bit and use the entire storage capacity continuously.

Note that the above explanation does not mention the synchronization system between the clock t8 and the clock pulse generator 26, and between the counter 1 and the counter 27, but since these can be used, they will not be explained here. omitted.

In addition, although the above embodiment is explained using a shift register, instead of this shift register, a delay line memory or a random access memory can be program-controlled by a processor, etc., and used as a circular memory that operates in the same way as described above. It is also possible to use

Next, station line acquisition in the present invention will be explained with reference to FIG.

The difference between Fig. 2 and Fig. 4 is that Fig. 4 is the circuit 65 of Fig. 2.
The illustration of the detailed circuit in the circuit 51 is omitted, and the circuit 51...
...71 parts have been added.

In FIG. 4, 1, 27 are counters, 2, 26 are clock pulse generators, 3, 4° 28 are decoders, 5, 10
, 54, 56, 6B is an inverter, 8, 11. 14, 1
5, 31.52° 53.57, 58, 59, 70 are AND gates, 7.9, 12, 32, 55, 62. T1 is an OR gate, 13 is a shift register, 19 and 25 are transformers, 19-2 and 19-3 are transformer 190 secondary windings, 2
9 is a telephone call circuit, 30.36 is a hook switch, 3
3.34 is the contact of the telephone key for selecting the central office line, 73 is the contact of the telephone key for holding, ■ is the power supply (south side), E is the power supply (same side, 40, 5
1.60 and 61 are flip-flop circuits, 63 is a transistor, 64 is a relay, 64-1 is its contact, 66 is a photocoupler, and 67-1, 67-2 is a dial contact.

In order to acquire the central office line, the manual input of central office line acquisition information from the telephone to the shift register 13 is the same as in the previous case.

Next, the output of the AND gate 53 obtained as above is passed through the OR gate 55 and the AND gate 58 allows only the output at the timing T8 to pass therethrough, and a flip-flop 60 is set.

Furthermore, when the input of the inverter 56 is at a low level (that is, there is no signal input) at the timing t1, the flip-flop 60 is reset.

Therefore, if the telephone key 33 is kept pressed, pulses are sent repeatedly from the telephone at the cycle of the counter 27, and only while the output of the shift register 13 is present, the flip
Flop 60 remains set and is reset when the signal is cut off.

By setting the flip-flop 60, its output terminal becomes bi-level, turning on the emitter-collector of the transistor 63 through the OR gate 62, operating the relay 64, and connecting its contact 64-1.

As described above, a DC loop is formed for the station line and the station line is captured.

In addition, although FIG. 4 shows the case where there is only one station line and one voice talker, a circuit of 100a is connected in parallel to point A in the figure, and input signals t0 of AND gates 57 and 58 are inputted to t15 and t3, respectively.
By changing to t L5 j t7j t9, etc., multiple office lines can be selectively captured from the telephone.

If a large number of telephones are used, this can be done by connecting the circuit 200a in parallel to point A in the figure.

Next, the operation of a system for transmitting dial impulse information from a telephone to a central office line will be explained.

Dial contact information on the telephone is obtained by detecting the next change in loop current using a photocoupler 66 in the main device.

First, on the input side of the photocoupler 66, [(upper side of power supply 35 → secondary winding 19-2 of transformer 19 → hook switch 30 → dial contact (impulse contact) 67-1 →
Dial contact (shunt contact) 6L-2 → Input side of photo coupler 66 → Secondary winding 19-3 of transformer 19 → (→ side) loop of power supply 35, contact 6 is connected by dial operation
When 7-2 is connected and the contact 67-1 is connected, the DC current is interrupted, and due to the current change, dial information is output to the output side of the photocoupler 66.
The output signal is passed through an inverter 68 to an AND gate 5.
Control 3.

As a result, the AND gate 53 outputs the AND of the output signal from the shift register 13 and the photocoupler 66, and in the same manner as described above, the AND gate 53 outputs the OR gate 55 and the AND gate 57. ,5
8. Set or reset flip-flop 60 through the circuit of inverter 56.

Here, the cycle of the decoder 3 is set to be sufficiently small compared to the intermittent cycle of the contact 67-1.

This is so that even if the contact 67-1 is disconnected immediately after timing t2 and the inverter output 68 becomes low level, the flip-flop 60 continues to be set until t2 comes after the next cycle. .

Therefore, an error corresponding to one cycle of the maximum decoder 3 will occur.

The above conditions are necessary to reduce this error,
This can be made sufficiently small because it is determined independently of the transmission path between the telephone and the main device.

The operation of capturing the central office line has been described above, and next we will explain the operation of operating the hold telephone key on the telephone in this state to place the central office line on hold.

The hold information from the telephone is sent in the same way as the central office line acquisition information.

When the hold telephone key is pressed in the above-mentioned state of station line acquisition, the contact 73 becomes connected, and the signal T14 from the decoder 28 is passed through the contact 73 and input to the shift register 13 through the same route as described above.

At this time, the input time slot to the shift register 13 is tl t t2.

Next, the output signal of the shift register 13 sets the flip-flop 51 at the timing tl2.

Here, it is assumed that the clip flop 51 has an image format of 40.

Therefore, the flip-flop 51 at timing t1
Outputs bilevel from 2 to tl2 after the next cycle,
The output of the AND gate 52, which is the output of the AND gate 52, the output of the shift register 13, the station line capture information at the timing t2, and the timing C0 of the counter 1, is passed through the OR gate 55 and the point A (transmission bus) to the AND gate 52.
9 input.

On the other hand, with the arrival of the suspension information, the output of the AND gate 53, which has been output so far, is blocked by the inverter 54.

Therefore, the flip-flop 60 is reset, and the reset terminal R of the flip-flop 61 becomes low level.

Also, the output terminal Q of the flip-flop 60 becomes bi-level, and this, the signal from the point A, and the timing t2 cause the AND gate 59 to output, the flip-flop 61 is set, and its output Q is passed through the OR gate 62. , the transistor 63 is turned on, the relay 64 is driven, its contact 64-1 is connected, and the central line is held.

Here, the telephone keys 33, 34 and 73 are locked by pressing the commonly used interlocking telephone key, that is, the office line key, and when the held telephone key is pressed and released, when it is restored, the office line key is also restored. It is a structure.

Therefore, by releasing the held telephone key, the central office line and the held telephone key are restored, the contacts 33 and 73 are disconnected, the input signal to the shift register 13 is cut off, and it is cleared.

Therefore, flip-flop 60 is reset and flip-flop 61 remains set.

Next, when the central office line key is pressed again, the contact 33 becomes connected, and the flip-flop 60 is set in the same manner as in the case of acquiring the central office line, and the output Q resets the flip-flop 61 and holds it. is canceled.

The operations of calling, capturing, and holding a call on the central office line have been explained above, but the above-mentioned central office line acquisition method is not only used for simply acquiring the central office line, but also for transmitting other information, such as information on the short contact 67-2 of the dial. It can be applied as a means to eliminate the influence of the inductance of the primary winding of the transformer 25 when transmitting a dial impulse to the central office line, that is, when transmitting a dial impulse.

An example of the implementation circuit is shown in FIG.

The differences between Figure 5 and Figure 2 are 1.2, 3.4 from Figure 2.
is omitted, inverter 91, AND gates 92, 93
, flip-flop 94, transistor 95, contact 9
A relay 96 having 6-1.96-2 is added, and the insertion position of the contact 67-2 is changed.

Here, when the dial is wound up in FIG. 5, its contact 67-2 becomes connected, and in the same way as the operation described in FIG. 4, it is stored in the shift register 13 at the timing of cp, and it It is output at the same timing, and a voltage is applied to the base of the transistor 95 via the route [AND gate 53 → OR gate 55 → AND gate 92 → flip-flop 94 → base of transistor 95].
Turn it on, operate the relay 96, and its contacts 96-
1.96-2 are brought into contact, thereby shorting the primary winding of the transformer 25.

As a result of the above, it is possible to eliminate the influence of the inductance of the transformer 25 when transmitting dial impulses.

Next, a secret story in the method of the present invention will be explained.

FIG. 6 is an example of a secret circuit used in the method of the present invention. Comparing FIG. 2 and FIG. 6, FIG. 6 shows the circuit 20 of FIG.
0, part of shift register 13, and gate I
L14, OR gate 12, inverter 10, flip
A circuit constituted by a flop 40 is used as a circuit 201, a shift register 213, and gates 211 and 214.
, an OR gate 212, an inverter 210, and a flip-flop 240, and an AND gate 216, 21B, an inverter 215°254, and a flip-flop 251 are added to the circuit 30.
1 is a circuit similar to 201.

Also, 400 is an or gate. Here, in order for FIG. 6 to operate as a secret call circuit, when the telephone connected to the circuit 201 presses LK to enter a call on the office line when the office line is idle, it must be shifted as explained in FIG. 2. The station line selection information LK1 is manually stored in the register 213.

In this case, telephone calls using 201 are possible.

Next, in this state, when the telephone connected to circuit 301 attempts to enter a call on the central office line and presses the central office telephone key LK, the signal for LKl is input to flip-flop 340 as explained in FIG. Set and gate 311
is applied to one input of

Here, since the information stored in the shift register 213 is output at the timing of 11.12 as described above, it is [AND gate 218 → OR gate 400].
→ AND gate 316 → inverter 315 The signal is applied to the other input of AND gate 311 in such a way as to block the signal from flip-flop 400 .

Here, inverter 217 and AND gate 216 prevent AND gate 211 from being blocked by the output signal from shift register 213.

Therefore, input to the shift register 313 is blocked, so it is not possible to enter a talking state.

Also, in this state, the flip-flop 251 and shift register 313 have no output, and the inverters 254 and 354
The output of is at bilevel.

With the above operation, only the telephone that first captures a single central office line can communicate when the central office line is empty.

Next, in the state described above, only one telephone set can be connected to one central office line.

However, in actual use, there are times when it is desired to connect two or more telephones.

In this method, a method for implementing this will be described below.

When the telephone key HK mounted on the telephone is pressed in Fig. 6, the contact HK becomes connected, and the signal 7i is sent to the main device in the same manner as described above, and the shift register is activated at the timing shown in Fig. 3, 5 and 6. 13.

The HK information stored in the shift register 213 is L1□
, t02, and sets the clip flop 251.

Here, the flip-flop 251 is a D-type flip-flop that is set by the trigger pulse t12.

The output of flip-flop 251 then goes high, which is applied to AND gate 218 through inverter 254 to prevent the output signal of shift register 213 from passing through it.

As a result of the above, the output signal of the OR gate disappears, and the LK information can be input to the shift register 313.

The above operation allows two or more telephones to make calls on one central office line.

Although the central office line in the above description has been described as a subscriber line connected to an exchange, the present invention can be applied to an extension line of a private branch exchange also being regarded as the central office line.

As explained above, the present invention provides a confidential communication system in a button telephone device that is compact, high quality, inexpensive, and can be implemented in the main device, and has great practical effects.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the overall configuration of the system of the present invention, Fig. 2 is a circuit diagram for explaining the communication system in the system of the present invention, Fig. 3 is a time chart for explaining the operation, and Fig. 4 is a diagram of the system of the present invention. FIG. 5 is a circuit diagram showing a partial modification of the circuit in FIG. 4; FIG. 6 is a circuit diagram for explaining secrets in the system of the present invention. It is.

Claims (1)

[Scope of Claims] 1. In a key telephone device in which a plurality of key telephones are selectively connected to a main device and a plurality of office lines using a plurality of call lines and a plurality of control lines, the main device includes: a first time slot pulse for generating a clock pulse, a plurality of rows of modulation/demodulation high speed time slot pulses corresponding to the office line, and a plurality of rows of low speed time slot pulses for control signal transmission corresponding to the control line;
a plurality of first time division switches connected to correspond to the plurality of office lines and controlled by corresponding pulse trains of the plurality of trains of modulation/demodulation high speed time slot pulses; a plurality of second time-division switches corresponding to button telephones, each connected to the communication line and controlled by a corresponding pulse train of the plurality of trains of modulation/demodulation high speed time slot pulses; A plurality of circulating memories corresponding to the button telephones connected to the plurality of second time division switches, and a slow time for transmitting control signals of the plurality of rows, which transmit control outputs transmitted from the corresponding button telephones via the control line. A plurality of writing means for writing to a corresponding one of the plurality of circulating memories in synchronization with a slot pulse, and corresponding only to the time when the output pulse of any one of the plurality of circulating memories is present when the output pulse exists. a plurality of feedback means compatible with the telephone for temporarily inhibiting said writing operation to said plurality of circular memories; and an output pulse from a corresponding one of said plurality of circular memories causes said plurality of feedback means to temporarily inhibit said write operation to said plurality of circular memories; a plurality of opening means for temporarily opening corresponding loops of the means, each of said telephones having a synchronous time slot pulse substantially synchronized with a corresponding one of said plurality of rows of low speed time slot pulses for transmitting control signals; a second pulse generator for generating a pulse, an operating means including a plurality of office line telephone keys corresponding to office lines, and an AND output between the output of the operating means and the synchronous time slot pulse to control the control from the corresponding button telephone. and a control output means for taking out an output, so that one of the central office lines designated by the control output sent by the designated operation of the central office line telephone key in any one of the button telephones 1. A secret telephone system for a button telephone device, characterized in that the key telephone device is connected in a time-division manner to a key telephone device, and is configured so that a central office line call can be carried out while maintaining confidentiality for other key telephone devices. 2. In a button telephone device in which a plurality of key telephones are selectively connected to a main device and a plurality of office lines using a plurality of communication lines and a plurality of control lines, the main device is provided with a clock pulse and a plurality of office lines. a first for generating a plurality of corresponding rows of modulation/demodulation high speed time slot pulses and a plurality of rows of slow time slot pulses for control signal transmission corresponding to the control line;
a plurality of first time division switches connected to correspond to the plurality of office lines and controlled by corresponding pulse trains of the plurality of trains of modulation/demodulation high speed time slot pulses; a plurality of second time-division switches corresponding to button telephones, each connected to the communication line and controlled by a corresponding pulse train of the plurality of trains of modulation/demodulation high speed time slot pulses; A plurality of circulating memories corresponding to key telephones connected to a plurality of second time division switches, and control outputs transmitted from the corresponding button telephones via the control line to the plurality of rows of low-speed time slots for control transmission. a plurality of writing means for writing to a corresponding one of the plurality of circulating memories in synchronization with a pulse, and corresponding only to the time when an output pulse of any one of the plurality of circulating memories exists, when the output pulse exists; a plurality of feedback means compatible with the telephone for temporarily inhibiting said writing operation to said plurality of circular memories; and an output pulse from a corresponding one of said plurality of circular memories causes said plurality of feedback means to temporarily inhibit said write operation to said plurality of circular memories; a plurality of opening means for temporarily opening corresponding loops of the means, each of said telephones having a synchronous time slot pulse substantially synchronized with a corresponding one of said plurality of rows of low speed time slot pulses for transmitting control signals; a second pulse generator for generating a pulse, an operating means including a plurality of office line telephone keys corresponding to office lines, and an AND output between the output of the operating means and the synchronous time slot pulse to control the control from the corresponding button telephone. and a control output means for taking out an output, so that one of the central office lines designated by the control output sent by the designated operation of the central office line telephone key in any one of the button telephones connected in a time-division manner to enable central office line calls to be carried out while keeping confidential calls to other key telephones, and further between the plurality of circulating memories and the feedback means, a deprivation telephone key provided in each of the plurality of telephones, the gate being operated by a signal at a predetermined timing and provided to block the output signal of the circulating memory, and for connecting the plurality of telephones to a central office line; and a second operating means such as
A button configured to operate a gate by the output of the second pulse generator and the second operating means to block the output of the circulating memory and to enable connection of a plurality of telephones to the same central office line. Confidential communication method for telephone equipment.