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RELATED APPLICATIONS
U.S. patent application Ser. No. 06/696,183, filed Jan. 29, 1985 in the
name of persons having an obligation of assignment to the assignee of the
present invention and commonly assigned herewith, and U.S. patent
application Ser. No. 722,359, filed 4/12/85, in the name of persons having
an obligation of assignment to the assignee of the present invention and
commonly assigned herewith.
FIELD OF THE INVENTION
The present invention relates generally to cordless telephones, and in
particular relates to a cordless telephone having a transfer capability
between units.
BACKGROUND OF THE INVENTION
The standard telephone consists of a base unit and a handset unit connected
to each other by an electrical cord. The base unit itself is connected by
another cord to a receptacle on a wall, telephone pole or a similar
immovable structure to which the telephone network line extends.
Therefore, the range of movement of the operator of the telephone is quite
limited. Even when the cords connecting the handset unit to the base unit
and the base unit to the wall are long, it can be cumbersome to move
either the entire telephone around to make calls from different locations
or to walk around with the handset unit once a call has been placed. The
simple fact that there is always a continuous physical connection between
the person making the phone call and the immovable wall or other fixed
structure can be a great inconvenience.
The cordless telephone represents a significant improvement over the
standard telephone. In the conventional cordless telephone, the base unit
is still connected to the receptacle on the immovable wall or the like by
a cord so that message signals from the telephone network line may be
received and transmitted. However, the handset unit of the cordless
telephone is an independently operative unit from which calls may be made
and by which calls may be received with no physical connection to the base
unit. Instead, the base unit and the handset unit of the cordless
telephone communicate with each other over a communication channel
established by the transmission and reception of electromagnetic waves,
conventionally radio waves. The handset unit may then be taken to
distances of up to 300 meters from the base unit, while still making and
receiving telephone calls.
The handset unit has a transmitting/receiving system or transceiver and a
loudspeaker in the earpiece and a microphone in the mouthpiece. In some
cordless telephones, the base unit also has either loudspeaker and
microphone incorporated within the base unit itself, or in an auxiliary
standard telephone connectable to both the base unit and the outside
telephone network line. When the base unit receives an incoming call, the
base loudspeaker/microphone can be used to converse directly with the
caller. Frequently such a cordless telephone has a transfer capability
wherein the incoming call is transferred from the base unit to the handset
unit to establish communication between the handset loudspeaker/microphone
and the telephone network line through the base unit, with the base
loudspeaker/microphone or auxiliary telephone being no longer in
communication with the telephone network line. By this means, an operator
at the base unit can receive an incoming call and can transfer it to a
second operator using the handset unit. This is an additional feature
making the cordless telephone even more convenient.
However, previously proposed cordless telephones having this transfer
capability have required a number of extra switches, so that the proper
operation thereof can be quite complicated. In one such cordless
telephone, when an incoming call is received, the operator at the base
unit depresses a hold key on the base unit to hold the outside line, and
then moves a mode switch to establish an intercom mode wherein the base
loudspeaker/microphone is in communication with the handset
loudspeaker/microphone. Then the base operator depresses a call key on the
base unit to send a signal to the handset unit to cause it to ring. If the
handset operator answers by depressing a key on the handset unit, the base
operator returns the mode switch from the intercom position and the hold
key is again depressed to release the incoming call, whereby the handset
loudspeaker/microphone receives the incoming call. On the other hand, if
the operator at the handset unit does not answer, the mode switch and hold
key are actuated in turn so that the loudspeaker/microphone of the base
unit again communicate with the incoming call.
This cordless telephone requires at minimum a hold key, a mode switch, and
a call key on the base unit. The higher the number of additional switches
and keys, the greater is the consequent complexity and manufacturing cost
of the cordless telephone. Furthermore, these switches and keys must be
exposed for easy access on the surface of the unit and thus there is a
possibility that they may be operated at the wrong time, in the wrong
order, or even inadvertently, with the result that the incoming call may
not be transferred to the handset unit, or in the worst case the incoming
call will be cut off.
Furthermore, there is no provision for transferring the call back from the
handset unit to the base unit, which would be a highly advantageous
feature adding considerably to the convenience of the cordless telephone.
Additionally, the previously proposed cordless telephones with transfer
capability have not had the capacity to establish three way communication
between the handset loudspeaker/microphone, the base
loudspeaker/microphone, and the telephone network line.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an
improved cordless telephone which eliminates the difficulties of the prior
art.
It is another object of the present invention to provide a cordless
telephone with a transfer capability by which an incoming telephone call
may be transferred from the base unit to the handset unit and from the
handset unit to the base unit.
It is another object of the present invention to provide a cordless
telephone with the aforesaid transfer capability which may be operated
easily and conveniently.
It is still another object of the present invention to provide a cordless
telephone with the aforesaid transfer capability having a minimum number
of actuable switches for performing this function.
It is yet another object to the present invention to provide a cordless
telephone having the aforesaid transfer capability wherein three-way
communication is possible between the handset unit, the base unit, and the
telephone network line.
In accordance with an aspect with of the present invention, there is
provided a cordless telephone comprising a base unit connectable to a
telephone network line for receiving and transmitting signals
therethrough, and a handset unit selectively mountable upon and separable
from the base unit. The base and handset units have respective transceiver
means for the transmission and reception of signals therebetween over
electromagnetic waves, the handset unit including handset
loudspeaker/microphone means and the base unit having base
loudspeaker/microphone means associated therewith. Connection means are
provided for selectively connecting the base and handset
loudspeaker/microphone means with the telephone network line and each
other and include hold means for reserving and releasing a telephone call
appearing on the telephone network line. First intercom key means is
actuable at the base unit, and first enabling means is actuable at the
base unit for enabling communication of the base loudspeaker/microphone
means with the handset loudspeaker/microphone means and the telephone
network line. The handset unit has second actuable intercom key means and
second actuable enabling means for enabling communication of the handset
loudspeaker/microphone with the base loudspeaker/microphone and the
telephone network line. Mode control means are operative for selectively
establishing a plurality of modes of the telephone including a telephone
mode wherein the hold means releases the telephone call and the
loudspeaker/microphone means of one of the base and handset units is in
communication with the telephone network line, and an intercom mode
wherein the hold means reserves the telephone call and the base and
handset loudspeaker/microphone means are in communication with each other.
At a time when the telephone is operated in the telephone mode with one of
the base and handset units in communication with the telephone network
line, the mode control means is responsive to actuation of the intercom
key means of that one unit to establish the intercom mode, and further, at
a time when the telephone is operated in the intercom mode, mode control
means is responsive to deactuation of the enabling means of one of the
base and handset units to establish the telephone mode with the
loudspeaker/microphone means of the other unit in communication with the
telephone network line.
In a first preferred embodiment of the cordless telephone according to the
present invention, the base loudspeaker/microphone means are constituted
by an auxiliary standard telephone connectable through the connection
means to both the telephone network line and the base unit. The enabling
means in this embodiment includes the conventional switch within the
standard telephone actuated when the receiver is lifted from or returned
to its crade.
In a second preferred embodiment of the cordless telephone according to the
present invention, the base loudspeaker/microphone means are incorporated
within the base unit itself, and the enabling means includes an actuable
switch and relay circuits within the base unit.
These, and other objects, features and advantages of the cordless telephone
according to the present invention, will become apparent from the
following detailed description of the preferred embodiments and the
accompanying drawings, throughout which like reference numerals designate
like elements and parts.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a cordless telephone of a type to which the
present invention may be applied, and with a handset unit being shown
separated from a base unit;
FIG. 2 s a flowchart illustrating the operation of a prior art cordless
telephone;
FIG. 3 is a block diagram illustrating a portion of the circuitry of a
handset unit of a cordless telephone according to a first preferred
embodiment of the present invention;
FIG. 4 is a block diagram illustrating a portion of the circuitry of a base
unit included in the cordless telephone according to the first preferred
embodiment;
FIG. 5 is a flowchart of a control program of the base unit of FIG. 4 when
operative for transferring an incoming telephone call from the base unit
to the handset unit;
FIG. 6 is flowchart of a control program of the handset unit of FIG. 3 when
operative for transferring an incoming telephone call from the handset
unit to the base unit; and
FIG. 7 is a flowchart of a simplified control program operative for
transferring an incoming telephone call from one unit to the other unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings in detail, and initially to FIG. 1 thereof, a
cordless telephone 10 of a type to which the present invention may be
applied is there shown to include a handset unit 1 and a base unit 2. Base
unit 2 is connected by a telephone cord 3 to an outlet or receptacle in a
wall, a telephone pole, or another fixed structure, so that it may both
receive and transmit telephone message signals through a telephone network
line 3a and also may be powered thereby. An antenna 100 on handset unit 1
and a corresponding antenna 200 on base unit 2 are used to create a
communication channel between the two units by the transmission and
reception of radio waves, schematically illustrated in FIG. 1 by the
arrows extending between the antennas. As is conventional, handset unit 1
includes a ten-key panel 151 for making or dialing outgoing calls, and a
mouthpiece 101 and an earpiece 102 with which a microphone and a
loudspeaker (not shown) are, respectively, associated. A telephone number
may be entered on ten-key panel 151, and corresponding information is
transmitted over the communication channel to base unit 2 and thence to
telephone network line 3a. Alternatively, when base unit 2 receives a
message signal from the telephone network line indicating that an incoming
call is present, a signal from base unit 2 causes a bell in handset unit 1
and a buzzer in base unit 2 to ring to indicate the existence of the
incoming call.
The standard maximum separation of such a handset unit 1 and base unit 2 is
about 300 meters, set by the Federal Communications Commission. The
frequencies of the radio waves transmitted therebetween are in the 40 MHz
band, and typically there are ten duplex channels permitted for each
system.
Before describing the structure and operation of the cordless telephone
according to the present invention, and in particular the advantageous
transfer capability thereof, it is instructive to consider the operation
of prior art cordless telephones with transfer capability. The operation
of the prior art cordless telephone mentioned in the Background section is
illustrated in FIG. 2 in the form of a flowchart. In this flowchart, the
physical actuation of the various switches and the operational steps of
the telephone are illustrated in the single bordered boxes, while the
resultant conditions of the telephone are illustrated in the double
bordered boxes. The transfer operation begins in step 21, during which
base unit 2 of the prior art cordless telephone is in communication with
telephone network line 3a. At this point, transmissions between the
loudspeaker/microphone or electro-audio-transducer of base unit 2 and
telephone network line 3a are permitted in a telephone mode of operation.
In step 22, a hold key, which may be a push button switch provided on base
unit 2, is depressed to hold the incoming telephone call. This reserves
the telephone call while permitting the transfer of signals between base
unit 2 and handset unit 1.
In step 23, a two position slide or mode selecting switch for changing over
between the telephone mode and the intercom mode is moved to its intercom
position to enable the intercom mode between the base and handset units.
In step 24, a non-locking call key is depressed to cause the base unit 2
to send a control signal to handset unit 1, which is responsive to the
received control signal to produce a bell sound, i.e. it rings. In step
25, base unit 2 determines whether or not handset unit 1 has answered,
conventionally by retransmitting back a second control signal indicating
an answer. If handset unit 1 answers, the procedure moves to step 26,
wherein the intercom mode of the cordless telephone is established and the
base unit operator can inform the operator at the handset unit of the
incoming call. In step 27, the mode switch is slid to its telephone mode
position, to recover the telephone mode of operation. In step 28, the hold
key is again depressed to release the incoming call, so that, in step 29,
handset unit 1 is now in communication with telephone network line 3a and
the handset unit operator can talk with the caller.
On the other hand, if in step 25 handset unit 1 does not answer, the
procedure moves to step 37, wherein the mode switch is slid to the
telephone mode position to recover the telephone mode, and in step 38 the
hold key is depressed to release the incoming telephone call. Thus in step
39, base unit 2 is once again in communication with telephone network line
3a, so that the base operator may talk with the caller.
Therefore, a hold key, a mode selecting switch and a call key are all
required on base unit 2 to transfer the incoming call from base unit 2 to
handset unit 1. These switches increase the manufacturing cost of the
cordless telephone, and are easily accessible and thus likely to be
inadvertently or incorrectly actuated. Clearly, from the illustrated
flowchart, actuation of the switches in the wrong order will not produce
the desired transfer from the base unit 2 to handset unit 1. The confusion
of operators in attempting to transfer incoming telephone calls from the
base unit to the handset unit with such a complicated system is well known
and constitutes a significant disadvantage in such prior art cordless
telephones. A cordless telephone 10 10 according to the present invention,
on the other hand, not only provides this transfer capability from the
base unit to the handset unit with only a single additional intercom mode
key, as will be described below, but provides an additional transfer
capability from the handset unit back to the base unit and enables
communication between all three of the handset unit, the base unit, and
the telephone network line.
Referring now to FIGS. 3 and 4, important portions of the circuitry
contained within handset unit 1A and base unit 2A, respectively, of a
cordless telephone according to the present invention are therein
illustrated. It should be noted that the circuitry within these two units
contains many corresponding elements, so that the two figures and their
accompanying description should be considered together.
Handset unit 1A (FIG. 3) has a transmission which includes a transmission
system 110 comprised of elements bearing reference numerals 111 to 115,
and a receiving system 120, comprised of elements bearing reference
numerals 121 to 128. Base unit 2A (Fig.4) similarly has a transceiver
which includes a transmission system 210 comprised of elements bearing
reference numerals 212 to 215, and a receiving system 220 comprised of
elements bearing reference numerals 221 to 227. Base unit 2A further
includes a connecting circuit 230, including elements 231 and 232, and
serving to connect the transmission system 110, the receiving system 120
and an auxiliary telephone 4 to telephone network line 3a. In the first
preferred embodiment, auxiliary telephone 4 having a receiver 4a is used
as the loudspeaker/microphone or electro-audio transducer associated with
base unit 2. For a better understanding of the present invention, the
function and operation of these elements will be described as signals are
transmitted between the two units. In the illustrated embodiment, the
signals are transmitted over a selected one of two allowed duplex
channels, A and B, each containing an upper channel and a lower channel.
Therefore, for the transmission of a signal from handset unit 1A (FIG. 3),
an audio signal St from a microphone 111 contained within mouthpiece 101
of handset unit 1A is supplied through an audio frequency amplifier 112 to
a frequency modulating circuit 113, which outputs a corresponding high
frequency FM signal Su in the upper channel of a selected one of duplex
channels A or B. For this purpose, frequency modulating circuit 113 is
provided with a channel selecting signal CH generated in accordance with
the operation of a channel selector switch 154. Channel selecting signal
CH may be used to determine the frequency of a local oscillator signal
used to frequency convert the FM signal to radio frequencies. Signal Su is
supplied through a high frequency amplifier 114 and a band pass filter 115
with a pass band including both upper channels to antenna 100, by which it
is transmitted as a radio frequency wave to base unit 2A over the
communication channel.
Referring now to FIG. 4, signal Su transmitted from handset unit 1A is
received at base unit 2A by antenna 200 and is supplied through a band
pass filter 221 and a high frequency amplifier 222 to a mixing circuit
223. Mixing circuit 223 receives a local oscillation signal from a local
oscillator circuit 224 receiving channel selecting signal CH to frequency
convert the signal Su to an FM intermediate frequency signal. This FM
signal is supplied through an intermediate frequency amplifier 225 to an
FM demodulating circuit 226, wherein it is demodulated to produce audio
signal St. Audio signal St is passed to telephone network line 3a through
an audio frequency amplifier 227 and the signal transmission circuit
comprising a hybrid circuit 231, and a relay circuit 232. Hybrid circuit
231 has solid state components and moving contacts to form a transition
between the electronic receiving system 220 and electromechanical relay
circuit 232. Relay circuit 232 includes a relay of the type to make and
break the connection between base unit 2A and telephone network line 3a,
and a hold relay which in a first position can hold a connection with
telephone network line 3a while disconnecting it from hybrid circuit 231
and auxiliary telephone 4, so that telephone communication with telephone
network line 3a is temporarily interrupted during an intercom operation
while keeping the incoming call available on telephone network line 3a.
This operation is referred to herein as reserving the incoming call. The
hold relay has a second position in which telephone network line 3a is
made available for connection to hybrid circuit 231, auxiliary telephone
4, or both. This operation is referred to as releasing the incoming call.
The transmission of signals from base unit 2A to handset unit 1A will now
be described. When incoming message signals are received from telephone
network line 3a, the audio signal Sr is supplied through relay circuit
232, hybrid circuit 231 and audio frequency amplifier 212 to a frequency
modulating circuit 213, which outputs a corresponding high frequency FM
signal Sd in the lower channel of the same duplex channel (A or B) as
signal Su. Frequency modulating circuit 213 is supplied with channel
selecting signal CH for this purpose. Signal Sd is supplied through a high
frequency amplifier 214 and a band pass filter 215 with a pass band
including the lower channels of both A and B channels to antenna 200, by
which it is transmitted to handset 1A over the communication channel.
Referring back to FIG. 3, signal Sd is received by antenna 100 and is
supplied through a band pass filter 121 with a pass band including both
lower channels and a high frequency amplifier 122 to a mixing circuit 123.
Mixing circuit 123 is supplied with a local oscillation signal from a
local oscillator circuit 124 receiving channel selecting signal CH, so
that signal Sd is frequency converted to an FM intermediate frequency
signal. This FM signal is supplied through an intermediate frequency
amplifier 125 to an FM demodulating circuit 126, wherein it is demodulated
to the audio signal Sr and supplied through an audio frequency amplifier
127 to an electro-audio transducer or loudspeaker 128 contained within an
earpiece of handset unit 1A.
In accordance with an important aspect of the present invention, handset
unit 1A further contains a control circuit, generally designated by
reference numeral 140 in FIG. 3, and base unit 2A similarly contains a
control circuit, generally indicated by reference numeral 240 in FIG. 4.
These control circuits may each advantageously be comprised in whole or in
great part by a microprocessor or microcomputer, contained on a single
integrated chip. An advantageous example is the MSM-6404 microcomputer IC
manufactured by Oki Electric Industry Co., Ltd. Control circuit 140
includes a central processing unit (CPU) 141, for 4-bit parallel
processing, a read only memory (ROM) 142, which stores control programs
for controlling the operation of CPU 141, a random access memory (RAM) 143
serving as a work and storage area, and input/output (I/O) port 144.
Similarly in base unit 2A, control circuit 240 includes a CPU 241, a ROM
242, a RAM 243 and an I/O port 244, each performing a function
corresponding to that of the element of control circuit 140 having the
same two final digits in the reference numeral. A detailed description is
given below of the operation and control of each of these elements, but it
should be understood that a control circuit such as control circuits 140
and 240 may, under the control of an appropriate control program, be
designed to perform different functions at different times and to control
the operation of several elements. At each stage of operation of the
control circuit by the control program, the control circuit may be viewed
as a means for performing a certain function. According to an important
aspect of the present invention, one of a plurality of operational modes
of the cordless telephone according to this invention may be established
in response to actuation of certain keys. At such time, control circuits
140, 240 may be regarded as mode control means for establishing a
telephone mode, an intercom mode, etc. Similarly, in accordance with
another aspect of the present invention, two identifying codes are
compared for identity to establish the communication channel, and at such
time control circuits 140, 240 may be regarded as identity detecting
means. The discussion below will make clear at all times what functions
control circuits 140 and 240 are performing and precisely how such
functions are carried out.
Connected to control circuit 140 and controlled thereby are ten-key panel
151, a talk switch 152, an intercom key 153, the above-mentioned channel
selector key 154, and a dip switch 155. Ten-key panel 151 has conventional
non-lock push button switches for inputting the telephone number to be
called. Talk switch 152 is a three position change-over switch used for
selecting an operational mode of handset unit 1A. When a movable contact
152a of talk switch 152 contacts fixed contact O (the OFF position), the
power is turned off to all the elements within handset unit 1A except
control circuit 140, to place handset unit 1A in an off mode. When movable
contact 152a contacts fixed contact S (the STANDBY position), control
circuit 140 is placed in a standby mode to await the signal Sd from base
unit 2A. When movable contact 152a contacts fixed contact T (the TALK
position), handset unit 1A is placed in a talk mode and the communication
channel between handset unit 1A and base unit 2A may be established.
Within the talk mode, handset unit 1A may be placed in a telephone mode,
an intercom mode, or a hybrid mode, as will be discussed below.
Channel selector key 154 is a non-lock push button switch for selecting
either channel A or B for the communication channel between handset unit
1A and base unit 2A. This signal specifies the desired upper or lower
channel by specifying the frequency dividing ratio of a variable frequency
dividing circuit contained within local oscillator circuit 124. Dip switch
155 may be an IC with pins selectively set by the operator to enter
respective binary values and is used by the operator to input a selected
identifying code ID to control circuit 140.
Intercom key 153 represents an important feature of the cordless telephone
according to the present invention, in that it provides an easily operated
transfer capability which is very convenient for the operator. Intercom
key 153 is a non-lock push button switch, and a detailed description of
its function will be given below in connection with FIGS. 5, 6 and 7. The
respective outputs from the push button switches forming ten-key panel
151, talk switch 152, intercom key 153, channel selector key 154 and dip
switch 155 are supplied to control circuit 140 for processing.
An MSK (minimum shift key) modulating circuit 161 is connected to control
circuit 140 for converting binary signals supplied thereto by control
circuit 140 to an MSK signal Sm in the audio frequency band. These binary
signals include identifying code ID, which will be described in greater
detail later, and a dial signal DS corresponding to the telephone number
entered through ten-key panel 151. Importantly, MSK signal Sm may also
include a control signal for indicating to base unit 2A that intercom key
153 has been depressed and that an incoming call is to be transferred. MSK
signal Sm is supplied to audio frequency amplifier 112 for transmission to
base unit 2A within signal Sd in the manner described above. The output of
FM demodulating circuit 126 is also supplied to a reception detecting
circuit 162 for detecting the presence or absence of signal Sd in the
output. As is well known, the frequency components of the output are
different in the presence or absence of signal Sd. A detection signal NSQ
generated by reception detecting circuit 161 when signal Sd is present is
supplied to control circuit 140.
Base unit 2A contains a similar MSK modulating circuit 261 for encoding the
identifying code ID, dial signal DS, channel selecting signal CH, the
control signal indicating an incoming call to be transferred, and other
signals in a signal Sm transmitted from base unit 2A to handset unit 1A.
In handset unit 1A, an MSK demodulating circuit 163 is supplied with the
output of FM demodulating circuit 126 to demodulate the identifying code
ID, control signal and other signals encoded in MSK signal Sm. The
demodulated signals are supplied to control circuit 140.
When an incoming call is detected in base unit 2A and signal Sd is
transmitted to handset unit 1A, signal NSQ is supplied to control circuit
140 and an appropriate signal is supplied to a call tone generator 164 for
generating a bell sound signal. The bell sound signal is supplied to audio
amplifier 127 to generate a bell sound, i.e. handset unit 1 rings.
Control circuit 140 also generates a control signal TX supplied to
frequency modulating circuit 113 to control whether or not FM signal Su is
output therefrom. As described in the commonly assigned related
applications cited above, the communication channel is established only
when identity between identifying codes stored in base unit 2A and handset
1A is detected. When identity is detected, signal TX enables frequency
modulated circuit 113 to output signal Su, whereas if identity is not
detected, signal TX disables frequency modulating circuit 113.
Control circuit 140 also generates a muting signal MUTE supplied to audio
frequency amplifier 127. As is conventional, muting signal MUTE is
produced when no telephone conversation is in progress, to prevent
extraneous noise from being generated and output through transducer 128.
Referring now to FIG. 4, control circuit 240 of base unit 2A is similar to
control circuit 140 of handset unit 1A and performs many corresponding
functions. Control circuit 240 provides similar means for detecting when
the two identifying codes, one stored in base unit 2A and one received
from handset unit 1A, are or are not identical, and for supplying control
signal TX to FM modulator 213 to establish or cut off transmission of
signal S.sub.d, respectively. Thus, control circuit 240 includes CPU 241,
ROM 242, RAM 243, and I/O port 244.
An MSK modulator 261, reception detecting circuit 262 and MSK demodulator
263 are provided which perform similar functions to the corresponding
elements in handset unit 1A, and will not be further described. A call
buzzer 266 is provided along with a locking push button switch 255 for
turning call buzzer 266 on and off. A tone generating circuit 264
generates a tone encode signal TE corresponding to the telephone number
for an outgoing call, which signal TE is supplied to audio frequency
amplifier 227 and thence to hybrid circuit 231 for transmission to
telephone network line 3a.
A bell sound signal detecting circuit 265 is connected to the telephone
network line 3a to detect an incoming bell sound signal indicating an
incoming call. The output BL of bell signal detecting circuit 265 is
supplied to control circuit 240.
A signal line 232' is provided between control circuit 240 and relay
circuit 232. In accordance with signals supplied from control circuit 240,
as discussed below, relay circuit 232 connects and disconnects hybrid
circuit 231 and auxiliary telephone 4 with telephone network line 3a and
reserves and releases the incoming call.
According to an important aspect of the present invention, an intercom key
253 is also provided on base unit 2A, and is operated in conjunction with
intercom key 153 on handset unit 1A to establish the telephone, intercom,
and hybrid modes. Auxiliary telephone 4 is connectable by relay circuit
232 to telephone network line 3a to constitute the base
loudspeaker/microphone or electro-audio transducer in the intercom
telephone system associated with base unit 2A.
When an outgoing call is to be made, the call can be placed either from
auxiliary telephone 4 or from handset unit 1A remote from base unit 2A. In
these cases, the operation of the cordless telephone is controlled by CPU
241 or by CPUs 141,241, respectively, under the control of control
programs stored in ROMs 142 and 242. The description below is given for
the second case, that is, the case in which a call is placed from handset
unit 1A by way of example. Initially, it is understood that handset unit
1A and base unit 2A have been set to the same channel A or B by
appropriate operation of channel selecting key 154.
To make an outgoing call, talk button 152 is placed in its TALK position so
that contact 152a contacts fixed contact T. An indication thereof is sent
to CPU 141, and control signal TX is generated to enable frequency
modulating circuit 113 to transmit a signal, which at this initial state
is an unmodulated carrier signal. CPU 141 then derives an identifying code
ID.sub.1 from RAM 143 which had been previously generated and stored
during an operation which will be described in detail below. Identifying
code ID.sub.1 is supplied to MSK modulating circuit 161, which converts it
to MSK signal Sm and supplies it to frequency modulating circuit 113.
Since frequency modulating circuit 113 is enabled to transmit signals,
identifying code ID.sub.1 is transmitted to base unit 2A in FM signal Su.
In base unit 2A, reception detecting circuit 262 generates detection
signal NSQ in response to the presence of signal Su, and thereupon control
circuit 240 enters a check mode to check for identity between the received
and stored identification codes. Signal Sm is derived from signal Su in FM
demodulator 226 and identifying code ID.sub.1 in signal Sm is derived in
MSK demodulator 263 and passed to CPU 241. CPU 241 then reads an
identifying code ID.sub.2 previously stored in RAM 243 and determines
whether or not the two identifying codes ID.sub.1 and ID.sub.2 are
identical. If they are not identical, which usually would mean that the
telephone call is being made by a handset of a different telephone set,
signal TX is adjusted to disable frequency modulating circuit 213 so that
further signal transmission is cut off and the cordless telephone remains
in the standby mode. On the other hand, if identification codes ID.sub.1
and ID.sub.2 are identical, frequency modulating circuit 213 remains
enabled to transmit signal Sd and to establish the communication channel.
In such case, control circuit 240 stops producing muting signal MUTE, so
that conversation may take place. Furthermore, since signal Sd is
transmitted back to handset unit 1A after identity of identifying codes
had been detected in base unit 2A, signal NSQ in handset unit 1A is
supplied to control circuit 140, which produces signal TX so as to enable
FM modulator 113 and further stops producing muting signal MUTE to release
audio frequency amplifier 127. Thus handset unit 1A is also enabled.
At this time, a dial tone is generated in handset unit 1A, and, upon
operation of ten-key panel 151, dial signaI DS corresponding to the
telephone number being dialed is generated in CPU 141 and supplied to MSK
modulating circuit 161 for conversion to MSK signal Sm and | | |
