Communication apparatus for generating a call signal from a telephone set to a data terminal

A call signal generating circuit includes a DC/DC converter, an ON/OFF control unit, including a control circuit and a phototransistor, for ON/OFF-controlling an output voltage from the DC/DC converter, and a polarity inverter cooperating with the control circuit, for switching polarities of an ON/OFF-controlled voltage. The ON/OFF timings of the ON/OFF control unit and a polarity switching timing of the polarity inverter are adjusted to generate a call signal having an arbitrary frequency.

BACKGROUND OF THE INVENTION: 
1. Field of the Invention 
The present invention relates to a communication apparatus having a 
function for generating a call signal or a communication apparatus to 
which another terminal can be connected. 
1. Related Background Art 
An INT or IR signal (repetition of ON for one second and OFF for two 
seconds) for interrupting a voltage of 75 V (16 Hz) is used as a call 
signal for ringing a bell of a telephone set. FIG. 3 is a circuit diagram 
showing a principle for ringing a bell of a telephone set. 
FIG. 4 is a diagram showing a conventional signal generating circuit for 
ringing a bell of a telephone set. 
This conventional signal generating circuit comprises a 16-Hz oscillator 
18, an amplifier 19, a control circuit 21, a gate 22 enabled/disabled in 
response to a control signal from the control circuit 21, an output 
transformer 20 for boosting an output from the amplifier 19, and a ring 
trip detect circuit 16 for monitoring whether output terminals 15-T and 
15-R connected to a telephone set are engaged by a DC circuit. The ring 
trip detect circuit 16 is a circuit for detecting a DC loop formed during 
transmission of a 16-Hz call signal (one second). The detect circuit 16 
integrates signals at the output terminals 15-T and 15-R and detects 
formation of a DC loop by determining a level of an integrated signal. 
In the conventional signal generating circuit, in order to ring a bell of a 
telephone set connected to the output terminals 15T and 15R, a control 
signal shown in FIG. 5(h) is supplied from the control circuit 21 to the 
gate 22. An output signal from the gate 22 is shown in FIG. 5(j). This 
signal is amplified by the amplifier 19, thereby obtaining an amplified 
signal shown in FIG. 5(k). The amplified signal is supplied to the 
boosting transformer 20 and the output terminals 15-T and 15-R, thereby 
ringing the bell of the telephone set. 
When a called party pickes up a handset of the telephone set, a DC circuit 
is formed. This DC circuit is detected by the ring trip detect circuit 16. 
A detection signal from the ring trip detect circuit 16 is supplied to the 
control circuit 21. The control circuit 21 stops generating the control 
signal supplied to the gate 22, and therefore the bell stops ringing. 
In the conventional arrangement, since the boosting transformer 20 is used 
at a low frequency of 16 Hz, utilization efficiency of the power source is 
poor. In addition, in order to reduce a loss of the boosting transformer 
20, the boosting transformer becomes bulky. As a result, the boosting 
transformer is expensive, and the mounting volume of the call signal 
generating circuit is undesirably increased. 
Telephone lines have been used for data communication of a facsimile 
machine and a teletex in addition to speech communication. A switching 
relay is arranged in a conventional facsimile machine to selectively 
connect a telephone set and the facsimile machine to the telephone line. 
The switching relay is switched under the control of a controller. In an 
automatic reception mode, when a call signal is received from a telephone 
line, the line is automatically switched from the telephone set to the 
facsimile machine to receive an image signal. 
The present applicant proposed a communication system for connecting the 
above-mentioned facsimile machine to a telephone set for exclusive use in 
a key telephone system in U.S. patent application Ser. No. 270,208. In 
this USSN, a call signal generating circuit and a ring trip detect circuit 
shown in FIG. 4 are arranged in the telephone set for exclusive use to 
automatically start the facsimile machine. However in this case, 
high-breakdown electronic components must be used in the call signal 
generating circuit and the ring trip detect circuit, as described above. 
In addition, generation of a dummy call signal and dummy response detection 
of the facsimile machine by ring trip detection must be performed. As a 
result, control procedures are undesirably complicated. 
In U.S. Ser. No. 270,208, the following procedures must be performed when a 
facsimile communication destination is called from a telephone set for 
exclusive use by using its dialing function. A basic arrangement of the 
system shown in U.S. Ser. No. 270,208 is shown in FIG. 6. 
(1) A handset of a telephone set 63 for exclusive use is set in an off-hook 
state to form a DC loop of a speech communication line 66 and an external 
line 61. 
(2) A telephone number of a destination to be called (speech communication 
destination) is input with telephone number buttons of the telephone set 
for exclusive use and is sent out onto the external line 61. 
(3) When a response of the destination facsimile machine is confirmed, the 
telephone set for exclusive use is operated to form a speech communication 
path by connecting the speech communication line 66 and a speech 
communication line 68 upon formation of a DC loop of the speech 
communication line 68 for connecting the telephone set for exclusive us 
and the facsimile machine. 
(4) When the handset of a telephone set 65 for general use is set in an 
off-hook state and a start button of a facsimile machine 64 is depressed, 
a DC loop is formed in the speech communication line 68. Therefore, the 
speech communication line 66 is connected to the speech communication line 
68 to set a facsimile communicable state. 
(5) Facsimile communication is performed between the facsimile machines. 
The above system, however, poses the following problems to be solved. 
(1) Both the telephone set 63 for exclusive use and the telephone set 65 
for general use must be prepared. 
(2) Unless the handset of the telephone set for general use is set in the 
off-hook state upon switching with the telephone set 63 for exclusive use, 
the start button of the facsimile machine 64 cannot be operated, thus 
inevitably requiring complicated procedures. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to solve the conventional problems 
described above and to improve a communication apparatus. 
It is another object of the present invention to provide a communication 
apparatus capable of generating a call signal with a simple arrangement. 
It is still another object of the present invention to simplify an 
arrangement when a call signal is sent to a data communication apparatus 
to start it. 
It is still another object of the present invention to simplify a system 
arrangement in a communication system for connecting a transmission line 
to a data communication apparatus through a communication apparatus. 
It is still another object of the present invention to simplify procedures 
for connecting a transmission line to a data communication apparatus in a 
communication system for connecting the transmission line to the data 
communication apparatus through the communication apparatus. 
The above and other objects, features, and advantages of the present 
invention will be apparent from the detailed description of preferred 
embodiments in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will be described in detail 
with reference to the accompanying drawings. 
A call signal generating circuit according to a first embodiment will be 
described below. 
FIG. 1 is a block diagram showing an arrangement of the call signal 
generating circuit of the first embodiment. The call signal generating 
circuit in FIG. 1 comprises a DC/DC converter A, a polarity inverter B, a 
ring trip detect circuit 16, and a control circuit 17. 
The DC/DC converter A comprises a high-frequency oscillation (HF OSC) 
circuit 1 for normally generating a signal having a frequency of 10 to 100 
kHz, a gate 2 for turning on/off an output signal from the high-frequency 
oscillation circuit 1, a switching element 3 of a bipolar transistor, an 
FET, or the like, a boosting transformer 4, a rectifying stack 5, a 
smoothing capacitor C1, a transistor TR1, a bias resistor R1 for this 
transistor TR1, and a phototransistor coupler 9. 
The polarity inverter B comprises photothyristor couplers 10, 11, 12, and 
13, and a resistor R2. 
The control circuit 17 and the gate 2 constitute an ON/OFF control means 
for controlling ON (one second) and OFF (two seconds) times of an output 
voltage from the DC/DC converter A. The control circuit 17 and the 
phototransistor 9 constitute a means for controlling ON and OFF times of 
the ON-controlled voltage at 16 Hz. The control circuit 17 and the 
photothyristor couplers 10, 11, 12, and 13 constitute a means for 
alternately inverting the polarities of the ON/OFF-controlled voltage. 
Note that the control circuit 17 comprises a microcomputer, a ROM, a RAM, 
and the like. 
An operation of the call signal generating circuit shown in FIG. 1 will be 
described below. 
FIG. 2(a) to 2(f) are timing charts of the signal waveforms of the main 
parts in the circuit shown in FIG. 1. More specifically, FIGS. 2(a) to 
2(f) show signal waveforms indicated by portions a to f in FIG. 1, 
respectively. 
The high-frequency oscillation circuit 1 outputs a high-frequency signal 
shown in FIG. 2(a). The control circuit 17 outputs a control signal shown 
in FIG. 2(b) to the gate 2. During the ON time of this control signal, the 
high-frequency signal drives the switching element 3 and switches the VCC 
(DC 24 to 48 V) through the boosting transformer 4. Therefore, a 
high-frequency voltage of about 75 V is induced at the secondary winding 
of the transformer 4. 
The high-frequency voltage of about 75 V is rectified by the rectifying 
stack 5 and smoothed by the capacitor C1, thereby obtaining a high DC 
voltage (about 75 V). The control circuit 17 controls the photocoupler 9 
and outputs a high voltage (about 75 V) at a timing when the transistor 
TR1 is turned on/off by the photocoupler 9. 
The control circuit 17 turns on/off the photothyristor couplers 10 to 13 at 
timings shown in FIGS. 2(d) and 2(e) and generates an AC signal (signal in 
FIG. 2(f)) whose polarities are alternately inverted at a period of 16 Hz. 
This AC signal is used to ring the bell of the telephone set. 
The resistance of the resistor R2 is determined to cause the ring trip 
detect circuit 16 not to detect a DC loop when the handset of the 
telephone set is not set in an off-hook state or when the DC loop is not 
formed in a data communication apparatus such as a facsimile machine, but 
to sufficiently detect the DC loop when the handset of the telephone set 
is set in the off-hook state. When the ring trip detect circuit 16 detects 
a ring trip, the control circuit 17 stops the above operation to interrupt 
ringing of the bell of the telephone set. 
In the arrangement of FIG. 1, the photothyristor couplers 10 to 13 are used 
to convert a high DC voltage into an AC voltage. However, in place of the 
couplers 10 to 13, another switching element such as a relay, a 
transistor, or a triac may be used. In addition, a switching element 
(e.g., an FET or a bipolar transistor) through which little leak current 
flows may be used in place of the coupler. In this case, the high voltage 
need not be turned on/off by the transistor TR1. 
In the arrangement of FIG. 1, the transistor TR1 turns on/off the high DC 
voltage on the secondary side of the transformer 4 to block a continuous 
flow of current through thyristor couplers 10 to 13. However, the 
transistor TR1 may turns on/off the high DC voltage on the primary side of 
the transformer 4. 
Furthermore, the frequency of the signal from the high-frequency 
oscillation circuit 1, the value of the VCC, the boosting ratio of the 
transformer 4, and the frequency of the signal for ringing the bell may be 
arbitrarily selected. 
According to the call signal generating circuit as described above, 
utilization efficiency of the power source can be improved, and the 
circuit size can be made compact. 
An arrangement including the above-mentioned call signal generating circuit 
in a telephone set which sends out a call signal to a facsimile machine 
and has a function for switching a transmission line to the facsimile 
machine will be described as a second embodiment of the present invention. 
FIG. 7 is a block diagram showing an arrangement of the telephone set of 
the second embodiment. 
Referring to FIG. 7, this arrangement includes a telephone set 75 for 
general use, and a facsimile machine 82 as an apparatus for performing 
communication except for speech communication. Switching between the 
telephone set 75 and the facsimile machine 82 is performed by a switching 
unit 88. The switching unit 88 may be arranged in the telephone set 75, 
but must be located at least near the telephone set 75, so that the user 
can manually switch the line connection. 
Whether a telephone line 72 is connected to the telephone set 75 or the 
facsimile machine 82 is controlled by two relays RL1 and RL2. The control 
contact of the relay RL2 is connected to the telephone line 72, and the 
telephone set 75 is connected to one of the contacts of the relay RL2. 
The other contact of the relay RL2 is connected to one of the contacts of 
the relay RL1. The control contact of the relay RL1 is connected to a 
two-wire signal line 81 between the telephone set and the facsimile 
machine 82 through a DC loop detect circuit 74 for detecting a call 
operation of the facsimile machine 82. 
The other contact of the relay RL1 is connected a DC supply circuit 73 for 
forming a dummy and a series circuit of a call signal send circuit 89 for 
sending a dummy call signal to the facsimile machine 82 and a ring trip 
detect circuit 80 for detecting a response of the facsimile machine 82. 
An operation of the above circuit arrangement is controlled by a control 
unit 76 including a microprocessor or the like. The control procedures of 
the control unit 76 are stored in a ROM 76a. 
The switching unit 88 has two modes of operation. More specifically, the 
first mode is a mode for normally connecting the facsimile machine 82 to 
the telephone line 72 to usually perform facsimile communication by 
utilizing an automatic outgoing/incoming call operation of the facsimile 
machine 82. The second mode is a mode for performing an incoming call 
operation by the telephone set 75 and switching the line at the time of 
communication for the facsimile machine 82 since the telephone line 72 is 
commonly used by the telephone set 75 and the facsimile machine 82. 
This mode switching is performed by a selection key 77. A transfer key 78 
is arranged to transfer a call to the facsimile machine 82 since the 
incoming mode is set to always receive a call to the telephone set 75. 
An operation of the above arrangement will be described below. When the 
automatic communication mode of the facsimile machine 82 is set by the 
selection key 77, the relays RL1 and RL2 are connected to the lower and 
upper contacts, respectively, so that the facsimile machine 82 is directly 
connected to the telephone line 72. 
However, when a manual incoming call operation of the telephone set 75 is 
performed by the selection key 77, the control procedures shown in FIG. 8 
are performed by the control unit 76. These procedures are stored in the 
ROM 76a. 
In this mode, the relay RL2 is connected to the telephone set 75. When a 
call signal is sent from the telephone line 72 in step S21 of FIG. 8, the 
bell of the telephone set 75 is rung in step S22. 
When the telephone set 75 is not set in the off-hook state in step S23, the 
bell is kept rung until disabling of the call signal is detected in step 
S34. When the telephone set 75 is set in an on-hook state, i.e., no one 
answers the telephone, the calling station stops generating the call 
signal in step S34, and then the bell stops ringing in step S35. 
When the telephone set 75 is set in the off-hook state, i.e., when someone 
answers the telephone, the flow advances to step S24. The call signal on 
the telephone line is disabled in step S24, and ringing of the bell of the 
telephone set 75 is stopped in step S25. The called party listens to 
signal tones from the calling party in step S26 and judges whether the 
calling party wishes facsimile communication. If the calling station is 
not a facsimile machine, speech communication is performed in step S36. 
Communication is then ended by the on-hook operation in step S37. 
When the calling station is a facsimile machine, the operator depresses the 
transfer key 78 in step S27, and then a call signal send routine in step 
S28 is executed. After the control unit 76 connects the relay RL1 to the 
upper contact (FIG. 7) and causes the call signal send circuit 89 to 
output to the facsimile machine 82 through the ring trip detect circuit 80 
the same call signal as that sent by the call signal send circuit 89. 
Therefore, the facsimile machine 82 is called by a dummy call signal. 
In step S29, the response of the facsimile machine 82 is monitored by the 
ring trip detect circuit 80. When the facsimile machine 82 actually 
responds to the dummy call signal, the control unit 76 stops generating 
the call signal in step S30. 
During the operations in steps S28 to S30 surrounded by a broken line in 
FIG. 8, the relay RL2 is connected to the telephone set 75, and a DC loop 
is held by the telephone set 75. When the response of the facsimile 
machine is detected, the relays RL1 and RL2 are connected to the lower and 
upper contacts, respectively, in step S31. Therefore, the telephone line 
72 is connected to the facsimile machine 22. 
Communication through the facsimile machine 22 is started. During facsimile 
communication, a state of a DC loop is kept monitored by the DC loop 
detect circuit 74. When the DC loop is released, the control unit 76 
detects that the facsimile machine 22 is disconnected from the telephone 
line. In step S33, the relays RL1 and RL2 are recovered, and the 
processing is ended. 
FIG. 9 is a flow chart showing the call signal send routine in step S28. 
The relationship of connection between the control unit 76 and the call 
signal send circuit 89 (the DC/DC converter A and the polarity inverter B 
in FIG. 1) is the same as that in FIG. 1. 
A call signal send operation will be described with reference to the flow 
chart in FIG. 9. 
In this operation, an AC output voltage has a period T, and this period is 
divided into eight time slots. The outputs c, d, and e (FIG. 1) are 
ON/OFF-controlled at timings 3T/8, T/8, 3T/8, and T/8. In step S28-1, a 
counter I is set to 0. In step S28-2, a T/8 timer is started. The outputs 
c, d, and e are ON/OFF-controlled by the counts of the T/8 counter in 
steps S28-3 to S28-6. In step S28-7, the control unit 76 waits until the 
timer is over. When the timer is over, the counter value is incremented in 
step S28-8. When the counter value becomes 8 in step S28-9, the counter 
value is set to 0 again in step S28-10. The control unit 76 determines in 
step S28-11 whether the AC output is stopped due to the end of ringing 
internal of the bell or ring trip detection. When the AC output is kept 
generated, the flow advances to step S28-2. Otherwise, the flow is 
branched into step S28-12. The outputs c, d, and e are disabled, and the 
flow is ended. Therefore, the call signal shown in FIG. 2(f) is generated. 
Note that T =1/16 Hz in FIG. 2(f). 
Referring to FIG. 9, the timer is a programmable timer, and the period T 
can be arbitrarily set. When the period T is arbitrarily changed, the 
period of the call signal can be variably set. In general, periods of call 
signals and their voltage standards vary in various countries. According 
to this embodiment, the value of the period T can be arbitrarily set, so 
that different requirements depending on various countries can be easily 
satisfied. 
The control circuit 17 of FIG. 1 (the same as the control unit 76 in FIG. 
7) outputs a control signal for controlling a duty ratio to the 
high-frequency oscillation circuit 1 and the high-frequency oscillation 
circuit 1 changes a duty ratio of a pulse output from the oscillation 
circuit 1 in accordance with the control signal. Therefore, the voltage of 
the call signal can be variably controlled. Software processing of the 
control circuit 17 can cope with various voltage standard requirements 
depending on various counties as in the various requirements for the 
periods. 
The arrangement of the call signal generating circuit can be simplified 
according to the second embodiment. 
According to the second embodiment, however, high-breakdown electronic 
components are required for the call signal send circuit 89 and the ring 
trip detect circuit 80 in order to generate a 16-Hz, 75-Vrms AC signal as 
a call signal. 
In addition, according to the second embodiment, generation of the dummy 
call signal and facsimile response by ring trip detection must be 
performed. Therefore, the control procedures of the control unit 76 are 
complicated. 
A communication apparatus capable of starting communication equipment such 
as a facsimile machine without using a high-voltage, low-frequency call 
signal will be described according to a third embodiment of the present 
invention below. 
FIG. 10 is a block diagram showing an arrangement of a communication 
apparatus according to the third embodiment. 
A switching unit 71 in FIG. 10 corresponds to the switching unit 88 in FIG. 
7. The switching unit 71 does not include a call signal send circuit 89 
and a ring trip detect circuit 80. Instead, a relay 79 (RL3) for 
performing incoming call transfer to a facsimile machine 82' in a manual 
incoming mode is arranged in the switching unit 71. Other arrangements of 
the communication apparatus in FIG. 10 are the same as those in FIG. 7. In 
FIG. 10, a ROM 76a is separated from a control unit 76'. However, the ROM 
76a may be arranged in the control unit 76' in the same manner as in FIG. 
7. 
The facsimile machine 82' has substantially the same arrangement as a 
conventional facsimile machine. More specifically, the facsimile machine 
82' comprises an image I/O unit 97 including a printer and an imaqe 
scanner, an image communication process unit 95 including a modem, a modem 
93, a dialing circuit 92 for automatically calling a desired station, and 
an incoming detect circuit 94. 
The facsimile machine 82' has the same arrangement as the conventional 
facsimile machine except for the arrangement and operation of the incoming 
detect circuit 94. The facsimile machine 82' is connected to the switching 
unit 71 through a four-wire connecting cable 90 unlike in the case of FIG. 
7. 
The connecting cable 90 comprises a known cable having modular jacks at its 
both ends. Such a cable generally has six wires. Two of the six wires are 
used to connect the switching unit 71 to the DC loop detect circuit 74 and 
a relay RL4 in the facsimile machine 82'. Other two wires are used to 
control the contacts of the relay 79 in the switching unit 71. 
The relay RL4 is used to switch an incoming/outgoing state of the facsimile 
machine 82' and connects the DC loop detect circuit 74 in the switching 
unit 71 to the dialing circuit 92 or the incoming detect circuit 94. In a 
normal automatic incoming state, the relay RL4 is connected to the 
incoming detect circuit 94. When a call command is input from the 
facsimile machine by a predetermined operation, the relay RL4 is connected 
to the dialing circuit 92. 
The incoming detect circuit 94 in the facsimile machine 82' detects a call 
signal input through the relay RL4. The incoming detect circuit 94 
includes a capacitor for extracting only an AC component of the 
transmission line, a photocoupler for detecting a 16-Hz call signal, and a 
monostable multivibrator for converting a photocoupler output to a pulse 
signal having a predetermined pulse width in accordance with a 
predetermined logic value. The incoming detect circuit 94 outputs a pulse 
signal upon detection of the call signal. The detection pulse signal is 
input to the control unit 96 in the facsimile machine 82' through an OR 
gate 94a. The OR gate 94a simultaneously receives a contact signal input 
through the cable 90. More specifically, electrical connections are made 
such that one contact is pulled up to the power source voltage, and this 
voltage level is supplied to the OR gate 94a in accordance with the ON/OFF 
operation of the contact. 
The incoming state can be signaled to the facsimile machine 82' in 
accordance with the contact states of the relay RL3 without generating a 
low-frequency, high-voltage call signal from the switching unit 71. 
An operation of the apparatus having the above arrangement will be 
described in detail. 
FIG. 11 shows control procedures of the control unit 76' in the switching 
unit 71. These control procedures are stored in the ROM 76a. Referring to 
FIG. 11, the same reference symbols as in FIG. 8 denote the same 
procedures, and a detailed description thereof will be omitted. The 
procedures in FIG. 11 which are different from those in FIG. 8 are steps 
S48 to S50 surrounded by a broken line. Steps S48 to S50 correspond to 
steps S28 to S30 in FIG. 8. 
When the switching unit 71 is set in the manual incoming mode, the manual 
incoming operation by the telephone set 75 is performed in the same manner 
as in FIG. 8. In step S26, when the operator judges facsimile 
communication, the operator depresses the transfer key 78 in step S27. The 
control unit 76' advances to step S48 and operates the relay 79 (RL3). 
Upon the operation of the relay 79, the same incoming detection signal as 
the call signal supplied from the telephone line is supplied to the 
control unit 96 through the OR gate 94a. The control unit 96 in the 
facsimile machine 82' starts an incoming call operation. In this case, a 
DC loop is formed by circuits (not shown) in the facsimile machine 82'. 
This DC loop is detected by the DC loop detect circuit 74 in step S49. 
The control unit 76! advances to step S50 by the DC loop detection signal. 
The relay 79 is recovered to a normal state, and the flow advances to step 
S31. The telephone line 72 is connected to the facsimile machine 82' by 
the relays RL1 and RL2 in the same manner as in the procedures in FIG. 8. 
Thereafter, facsimile communication is started from step S32. 
When an outgoing call is made by the facsimile machine 82', the facsimile 
machine 82' forms a DC loop upon predetermined key input operations. This 
DC loop is detected by the DC loop detect circuit 74, and the control unit 
76' controls to switch the telephone line 72 to the facsimile machine 82' 
through the relays RL1 and RL2. The end of communication is determined by 
the absence of the DC loop as in the conventional detection technique. 
When the telephone line is always connected to the facsimile machine 82' by 
the selection key 77, i.e., when the automatic incoming/outgoing call mode 
is set, the telephone line 72 is always connected to the facsimile machine 
82' through the relay RL1. Even if the operator is out, an automatic 
facsimile incoming/outgoing call operation can be performed. 
As described above, since an incoming call can be signaled to the facsimile 
machine 82' through the contacts without using the same call signal as 
that appearing on the telephone line, a process circuit which generates a 
high-voltage, low-frequency signal can be omitted from the switching unit 
71. Therefore, a simple, compact, lightweight apparatus can be obtained. 
At the same time, the power consumption of the apparatus can be reduced. 
In addition, the number of high-breakdown elements can be reduced, 
resulting in low cost. 
The facsimile machine 82' is simply modified by adding an OR gate to the 
incoming detect circuit 94. Therefore, the cost of the facsimile machine 
82' is not increased. 
In the above embodiment, the incoming call is signaled from the switching 
unit 71 to the facsimile machine 82' through the contacts However, the 
incoming signal may be sent using a photocoupler. 
When the signal is insulatively sent through the contacts or using the 
photocoupler, an incoming call detection error caused by common mode noise 
can be prevented. 
In the above embodiment, the telephone lines for the switching unit 71 are 
those of telephone sets for general use. However, a switching unit 71 may 
be arranged in a telephone set for exclusive use. In other words, the 
above arrangement may be applied to part of a PBX (Private Branch 
Exchange). A communication apparatus except for the telephone set is not 
limited to a facsimile machine but can be a data terminal. 
According to the third embodiment, the communication equipment can be 
started without using the same high-voltage, low-frequency call signal as 
that appearing on the telephone line. The circuit for generating the 
high-voltage, low-frequency signal can be omitted. A simple, low-cost, 
compact, lightweight apparatus can be obtained. Since the incoming 
detection signal for starting the communication equipment is insulatively 
input, an operation error of the communication equipment can be 
eliminated. In addition, a modification of the communication equipment can 
be minimized to result in low cost. 
A communication apparatus having simple connection procedures and a simple 
circuit arrangement when a data communication apparatus (e.g., a facsimile 
machine) is connected to a telephone line through the communication 
apparatus will be described as a fourth embodiment of the present 
invention. 
FIG. 12 is a schematic block diagram of the fourth embodiment. The same 
reference numerals as in FIG. 6 denote the same parts in FIG. 12, and a 
detailed description thereof will be omitted. 
Referring to FIG. 12, this apparatus includes a telephone set 101 for 
exclusive use as an extension telephone set. An accessory telephone set 
(telephone set for general use) of a facsimile machine 64 is omitted. A 
line output terminal (T terminal) for connecting the telephone set 101 and 
a telephone set 65 of the facsimile machine 64 is connected to the 
telephone set 101 as if a telephone set for general use is connected when 
viewed from the facsimile machine 64. More specifically, the T terminal is 
a two-wire line connection terminal. When the facsimile machine 64 is 
started, the telephone set 101 forms a DC loop in the connecting lines (DC 
loop forming lines). The telephone set 101 is a telephone set compatible 
with a standard interface of a main control unit 62. An exclusive 
interface need not be required. 
The facsimile machine 64 used in this embodiment can be set in a 
manual/automatic send mode. When the manual send mode is to be set, 
dialing is performed such that a telephone number is keyed in from an 
accessory telephone set connected to the facsimile machine 64. In this 
case, the same dialing operation can be performed by a key-in operation at 
the telephone set 101 in place of the accessory telephone. 
In the automatic send mode, a DC loop with a telephone line 68 is formed to 
call the telephone set 101. The telephone line 68 is connected to a 
telephone line 66, and the main control unit 62 connects the telephone 
line 66 to an external line 61. Therefore, information for the telephone 
number signal from the facsimile machine 64 is directly sent on the 
external line 61. 
A detailed arrangement of the telephone set 101 of the fourth embodiment is 
shown in FIG. 13. 
A speech communication circuit 121 performs impedance matching with the 
telephone line 66 and sends a speech signal from a handset 122 onto the 
telephone line 66. At the same time, the speech information from the 
telephone line 66 is output to the handset 122. A call signal generating 
circuit and DC supply circuit 123 for outputting a call signal to the 
facsimile machine 64 and calling the facsimile machine 64 upon reception 
of facsimile communication, and for supplying a DC power to monitor a DC 
loop. A DC loop monitor circuit 124 monitors a DC loop with the telephone 
line 68 during facsimile communication including automatic sending of the 
facsimile machine 64. A DC loop monitor circuit 125 detects a DC loop with 
the telephone line 68 which is formed by a DC loop forming circuit 126 or 
the facsimile machine itself. An operation unit 127 includes telephone 
number keys, and a selection key for connecting the facsimile machine 64 
and the telephone line 66. A control circuit 128 controls the overall 
telephone operations in accordance with key input operations of the 
operation unit 127 and control signals from a control line 67. 
A relay circuit 129 is operated to switch the telephone line 66 to the 
speech communication circuit 121 (i.e., the telephone set is used as a 
telephone set for general use) or the facsimile machine 64. A hook switch 
130 detects a on-/off-hook state of the handset 122. 
Facsimile send control of the fourth embodiment having the above 
arrangement will be described with reference to a flow chart in FIG. 14. 
In step S1, an original sheet is set on the facsimile machine 64. The 
handset 122 is set in the off-hook state in step S2 to form a DC loop with 
the telephone line 66. The main control unit 62 detects this DC loop and 
determines that a call request is made from the telephone set 101. The 
main control unit 62 captures an available subscriber telephone line 
(external line) to form a DC loop and requests a line connection to an 
exchanger as telephone network station equipment. When a plurality of 
external lines are connected to the main control unit 62, one of the 
external lines is selected by a line selection key or the like in the 
operation unit 127. Alternatively, a change in state such as an off-hook 
state of the telephone set 101 may be detected by the control circuit 128, 
and a detection signal may be sent from the control circuit 128 to the 
main control unit 62 through the control line 67. 
In step S3, a telephone number of the destination facsimile machine is 
input with telephone number keys on the operation unit 127. Input 
information from the operation unit 127 is detected by the control circuit 
128 and is sent to the main control unit 62 through the control line 67. 
The main control unit 62 generates a telephone number corresponding to the 
telephone number key input information sent through the control line 67 
and sends it to the captured external line 61. During the series of 
operations described above, various signal tones from the external line 
are relayed by the main control unit 62 and can be listened to at the 
handset 122 of the telephone set 101 through the telephone line 63. 
In step S4, the source side waits until the designation apparatus responds. 
The center exchanger which receives the telephone number signal calls a 
destination side by selecting a connecting line of a telephone set or an 
apparatus designated by the telephone number and waits until the 
destination side responds. When the destination side responds, the main 
control unit 62 informs the response of the destination side by using the 
control line 67 and forms a communication path with the designation 
apparatus, so that the source and designation apparatuses can communicate 
with each other. The flow advances from step S4 to step S5. A selection 
key for designating switching of the facsimile machine 64 is depressed at 
the operation unit 127. When the selection key is depressed, the control 
circuit 128 operates the DC loop forming circuit 126 in step S6. A DC loop 
with the T terminal is formed. At the same time, the relay circuit 129 is 
operated to connect the telephone lines 66 and 68. In this state, the user 
candepress the start button of the facsimile machine. The user depresses 
the start button of the facsimile machine as a call request from the 
accessory telephone (omitted in this embodiment). The facsimile machine is 
then connected to the line 68. 
In step S7, a start key of the facsimile machine 64 is depressed. A DC loop 
with the line 66 is formed in the facsimile machine 64, so that the 
facsimile machine 64 is connected to the line 66. For this reason, it is 
determined in step S8 whether the facsimile machine 64 is disconnected 
from a DC loop forming line 100 and connected to the telephone line 66. 
When the DC loop monitor circuit 125 detects a DC loop release upon 
detection of disconnection of the facsimile machine 64 from the DC loop 
forming line 100 (when the facsimile machine 64 starts facsimile 
communication), the flow advances from step S8 to step S9, thereby 
deenergizing the DC loop forming circuit 126. 
Necessary facsimile communication is then performed. When facsimile 
communication is ended, the facsimile machine 64 releases the DC loop 
formed with the line 68 so as to open the line. In step S10, the control 
circuit 28 waits until the DC loop monitor circuit 124 detects a DC loop 
release. When the DC loop is released and the end of communication is 
detected, the flow advances to step S11. The relay circuit 129 is 
recovered, and the line 66 is disconnected from the line 100. The line 66 
is connected to the speech communication circuit 121. The control circuit 
28 then determines in step S12 whether the hook switch 130 is set in an 
open state (i.e., the handset is set in an on-hook state) or an off-hook 
state. The control circuit 28 informs the main control unit 62 of the 
state of the hook switch 130. 
When the on-hook state is detected, the main control unit 62 releases a DC 
loop formed with the external line and recovers the line. However, when 
the off-hook state is detected, the main control circuit 62 maintains the 
speech communication state and recovers the line after the off-hook signal 
is received from the telephone set 101. 
In the above description, the line 66 is normally connected to the speech 
communication circuit 121. Manual calling and facsimile transmission by 
using the telephone set for exclusive use are exemplified. However, the 
present invention is not limited to the particular embodiment described 
above. The telephone line 66 may be normally connected to the telephone 
line 68, and the line 66 may be connected to the facsimile machine 64. In 
this case, the facsimile machine 64 can be set in an automatic/manual 
receive mode. 
Alternatively, the DC loop monitor circuit 125 is normally biased to 
immediately connect the lines 66 and 68 when a DC loop is formed by the 
line 68 connected to the facsimile machine 64. 
Switching control of the telephone set for exclusive use described above is 
performed by the separate main control unit 62. When the number of 
external lines is one, the main control unit need not be arranged as an 
independent unit. A facsimile adapter with a telephone set need only 
include a network control circuit for performing network control between 
the internal circuit arrangement of the telephone set and the external 
line. In this case, line control from the telephone set to the facsimile 
machine 64 can be performed with only operations at the telephone set. 
The above arrangement is shown in FIG. 15. 
Referring to FIG. 15, this arrangement includes a network control unit 131 
for controlling interface with an external line 61, a telephone set 132 
having the same arrangement as that in FIG. 13, and telephone lines 136 
and 137 having the same arrangements as the lines 66 and 67 in FIG. 13. 
According to this embodiment as described above, since the facsimile 
machine 64 is connected to the main control unit 62 through a telephone 
set for exclusive use which can be connected as standard equipment, a 
destination facsimile machine can be called (dialed) upon an operation of 
telephone number keys of the telephone set 101. A telephone set for 
general use which cannot be connected as standard equipment of the main 
control unit need not be connected to the facsimile machine 64. A new 
interface for the telephone set for general us need not be arranged. 
The line can be easily switched to facsimile communication upon depression 
of the start button of the facsimile machine after the destination 
responds to dialing from the telephone set 101. 
If a facsimile machine is of a portable type and is installed on a desk, 
the telephone set of this embodiment is connected thereto in place of the 
telephone set for general use. The network control circuit 131 may be 
arranged in the telephone set of this embodiment. Therefore, the main 
control unit 62 can be omitted, the apparatus structure can be simplified, 
and the space can be saved. 
The data communication equipment may be connected to a public telephone 
line and can allow communication upon an operation at the data 
communication equipment. 
According to the fourth embodiment as described above, the facsimile 
machine can be connected to an extension of the existing telephone control 
unit without adding a special interface circuit. 
A call signal generating circuit (FIG. 1) (i.e., the DC/DC converter A and 
the polarity inverter B) is arranged in the call signal generating circuit 
123 (FIG. 13) of the fourth embodiment to simplify the circuit 
arrangement. An arrangement obtained by applying the call signal 
generating circuit (FIG. 1) to the call signal generating circuit 123 
(FIG. 13) will be described as a fifth embodiment hereinafter. 
A detailed arrangement of a telephone set 101' for exclusive purpose 
according to the fifth embodiment is shown in FIG. 16. 
Referring to FIG. 16, a speech communication circuit 221 performs impedance 
matching with a line 66. The speech communication circuit 221 sends out a 
speech signal or the like from a handset 222 onto the line 66 and at the 
same time outputs a speech signal from the line 66 to the handset 222. 
The call signal generating circuit 223 (the DC/DC converter A and the 
polarity inverter B) shown in FIG. 1 is a circuit for outputting a call 
signal to a facsimile machine 64 in the facsimile communication incoming 
mode and will be described in more detail later. A DC supply and ring trip 
detect circuit 224 includes a DC supply circuit and a ring trip detect 
circuit. The DC supply circuit monitors formation of a DC loop upon 
starting of the facsimile machine. The ring trip detect circuit detects 
the response of the facsimile machine in response to the call signal. A DC 
loop monitor and dial signal detect circuit 225 monitors formation of a DC 
loop with a line 68 during facsimile communication including automatic 
transmission of the facsimile machine 64 and detects a dial signal. 
The DC loop monitor circuit 226 detects that formation of a DC loop with 
the line 68 by a DC loop forming circuit 227 is switched to loop formation 
by the facsimile machine itself. An operation unit 228 includes telephone 
number keys and a selection key for connecting the facsimile machine 64 to 
the line 66. A control circuit 229 controls the overall operation of the 
telephone set in accordance with key inputs from the operation unit 228 
and a control signal from a control line 67. 
A relay circuit 230 switches the line 66 to the speech communication 
circuit 221 (the telephone set is used to have an original telephone 
function) or to the facsimile machine 64. A hook switch 231 is interlocked 
with the on-/off-hook state of the handset 222. The control circuit 229 
can also monitor the state of the hook switch 231. 
With the above arrangement, the control circuit 229 performs the procedures 
shown in FIG. 9 and sends the call signal shown in FIG. 2(b) to the 
facsimile machine 64. In the fifth embodiment, facsimile transmission 
after manual calling with the telephone set 101' for exclusive use is the 
same as that in the fourth embodiment. 
The frequency and voltage of the call signal can be variably set by 
software in the fifth embodiment in the same manner as in the second 
embodiment. 
Facsimile reception control will be described with reference to a flow 
chart of FIG. 17 wherein the telephone set 101' for exclusive use is set 
in a facsimile automatic receive mode and the facsimile machine 64 is set 
in the automatic receive mode. 
In step S121, a call signal from a center exchanger reaches the external 
line 61. The main control unit 62 detects this call signal and informs 
reception of the call signal to the control circuit 229 of the exclusive 
phone 101' or telephone set for exclusive use through the control line 67 
(step S122). In step 123, the control circuit 229 performs the procedures 
shown in FIG. 9, drives the call signal generating circuit 223, and sends 
the call signal to the facsimile machine 64 through the line 68. In step 
S124, the control circuit 229 monitors the DC loop monitor circuit 225 and 
waits until the response from the facsimile machine 64 is received. When 
the facsimile machine 64 detects the call signal and forms a loop with the 
line 68, the DC loop monitor circuit 225 detects the DC loop and sends a 
DC loop detection signal to the control circuit 229. In step S125, the 
control circuit 229 operates the relay circuit 230 to connect the lines 66 
and 68. At the same time, the control circuit 229 informs the main control 
unit 62 of the response from the facsimile machine 64. In step 126, the 
main control unit 62 receives the information signal from the telephone 
set 101', responds to the call signal from the center exchanger to the 
external line 61, and connects the external line 61 and the line 66. In 
step S127, the center exchanger stops generating the call signal in 
response to a signal from the main control unit 62 and connects the 
external or exit line 1 to the call source line, i.e., the calling 
station, thereby forming a communication path between the source facsimile 
machine and the destination facsimile machine. In step S128, necessary 
facsimile communication is performed. When facsimile communication is 
ended, the facsimile machine 64 releases the DC loop formed with the line 
68 so as to release the line. Thereafter, the flow advances to step S10 in 
FIG. 14, and the line is recovered through the same processing as the 
manual send operation. 
In the above description, the line 66 is normally connected to the speech 
communication circuit 221 through the hook switch 231. Under this 
condition, manual calling and facsimile transmission with the exclusive 
telephone set are performed. In addition, the exclusive telephone set is 
set in the facsimile automatic receive mode. Under this condition, the 
automatic receive mode of the facsimile machine has been described. 
However, the present invention is not limited to the particular modes of 
operation described above. The lines 66 and 68 may be normally connected 
and the line 66 may be connected to the facsimile machine 64. Under these 
conditions, the facsimile machine 64 may be set in the automatic 
receive/send mode. 
Manual/automatic transmission/reception may be performed even if a 
facsimile machine without a T terminal to which the DC loop forming line 
100 cannot be connected is used. 
According to the fifth embodiment as has been described above, without 
degrading the convenient function of a telephone set for exclusive use in 
a key telephone system, the telephone set can be connected to the 
facsimile machine. Furthermore, since the call signal generating circuit 
is made compact, a telephone set for exclusive use connected to the 
facsimile machine can be made compact accordingly. 
In each embodiment described above, the facsimile machine is exemplified as 
a data communication apparatus. However, any communication apparatus such 
as a telex or teletex having an automatic start mode set in response to a 
call signal from a line can be used in the present invention. 
The present invention is not limited to the particular embodiments 
described above. Various changes and modifications may be made within the 
spirit and scope of the invention.