Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
MICROCOMPUTER CONTROLLED KEY TELEPHONE
LINE CIRCUIT
BACKGROUND OF T~E INVENTION
(1) Field of the Invention
The present invention relates to key tele-
phones and more particuarly to a microcomputer con-
trolled key telephone line circuit for use in a key
telephone system.
(2) Description of the Prior Art
Key telephone common circuits have tradi-
tionally been electromechanical in nature however
recently electronic versions of these circuits have
been patented. U.S. Patent 3,952,169 issued on April 20,
1976 to O. W. Vincent discloses the use of discrete
logic and solid state switches to perform the key
telephone functions. U.S. Patent 4,057,693 issued
on November 8, 1977 to R. J. Angner however is more
representative of the recent prior art. Angner uses
a custom large scale integration chip to replace the
logic which per~orms the key telephone common functions.
However this chip only controls the functions for
one line and is not suitable for use in a self-contained
key telephone system such as the Applicants' key tele-
phone system. Bell Telephone Laboratories has recentlydeveloped a Com-Key 416 key telephone system which
is similar to the Applicants' key telephone system.
However, in the Bell Com-Key system the common func-
tions are provided by multiple custom large scale
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integration chips designed specifically to perform
their limited purpose. Also these chips provide only
logic control and interrupt functions, while tone
ringers and clock circuitry are external to the large
5 scale integration chips. Also many of the required
timing functions are performed by resistor-capacitor
networks. Thus the Com-Key 416 key telephone system
uses a large number of balky components to perform
the key telephone line circuit functions.
Accordingly, it is an object of the present
invention to provide a novel, low cost, minimum com-
ponent technique of performing the key telephone line
circuit functions.
SUMMARY OF THE INVENTION
The microcomputer controlled key telephone
line circuit of the present invention provides the
standard key telephone functions such as line pickup,
hold and ringing detection, lamp illumination and
tone signalling. The use of microcomputer control
20 to provide these functions is a novel, low cost and
; highly efficient method of providing the standard
key telephone functions associated with a line circuit.
This circuit can be housed in a standard key telephone
and operates to control two lines and multiple stations.
The circuit consists of a microcomputer
connected between a ringing detection circuit, a line
relay, loop relay, an A-lead detection gate, a lamp
control gate and a common audible control gate for
each of two lines. The microcomputer continuously
30 scans the ringing detection leads and the A-lead detec-
tion leads to detect the presence of an incoming call
or the origination of an outgoing call. The status
of the A-lead indicates to the microcomputer either
the operation of a line pickup key or the operation
35 of a hold key associated with one of the stations
connected to the microcomputer. Upon detection of
an incoming call the microcomputer will output a lamp
flash signal to the lamp lead and a warble (two fre~
quency) tone to the common audible lead. Upon
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operation of a line pickup key the microcomputer will
output a steady lamp signal to the lamp lead and re-
move the warble tone from the common audible lead.
Upon operation of the hold key the microcomputer will
output a lamp wink signal to the lamp lead and will
apply a tone-on-hold signal to the tip and ring leads.
Thus the microcomputer provides the control ~unctions
of the line circuit, and generates the timing signals
and tone signals.
DESCRIPTION OE THE DRAWING
The single figure of the accompanying draw-
ing is a circuit diagram of a microcomputer controlled
key telephone line circuit in accordance with the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the accompaning d~awing,
the microcomputer controlled key telephone line circuit
of the present invention is shown connected to line
1 and line 2. The common circuit includes the series
combination of capacitor 101, resistor 102, zener
diodes 103 and 104, and capacitor 105 connected across
the tip and ring leads of line 1. Bridge 106 is also
connected across the tip and ring leads of line 1
and is further connected to the series combination
of line relay 107, contacts 12A and resistor 15.
Optical coupler 108 is connected across capacitor
105 and the base of phototransistor 108C is connected
to the parallel combination of capacitor 109 and
resistor 110. The emitter of phototransistor 108C
is connected to transistors 112 whose collector lead
is connected to microcomputer 10. The emitter lead
of transistor 112A is connected to microcomputer 10
via contact 107A. Similar circuitry is connected
between line 2 and microcomputer 10. Loop relay 12
is connected to microcomputer 10 via gate 11. The
A-lead associated with station one is connected to
microcomputer 10 via gate 13 and a lamp associated
with station one is connected to microprocessor 10
via gate 1~. The common audible lead, CAl, associated
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with station one is connected to gate 15 which is
connected to microcomputer 10 via leads W and Cl.
Line relay 107 is further connected to microcomputer
10 via contacts 12B. Similar circuitry is connected
between station two and microcomputer 10.
The operation of the microcomputer controlled
key telephone line circuit o~ the present invention
will be described with referenced to line 1 since
line 2 operations are identical to those of line 1.
This circuit controls the standard key telephone func-
tions such as line pickup, hold and ringing current
detection, lamp illumination and tone signalling.
Microcomputer 10 sequentially and alternately scans
the inputs from lines 1 and 2 every 10 milliseconds.
Thus it scans, for example, the A lead associated
with line lt followed by the A lead associated with
line 2, before scanning the next lead associated with
line 1.
When an incoming call is connected to the
line circuit, ringing current is applied to tbe tip
and ring leads, Tl (CO) and Rl (CO). Zener diodes
103 and 104 breakdown to this ringing signal voltage
and conduct current to optical coupler 108. Since
there are dead periods, during the zero crossing
transition, in a ringing cycle during which photo-
diodes 108A and 108B do not conduct, capacitor 109
supplies t~e base current to phototransistor 108C
during these dead periods. Phototransistor 108C thus
turns on in response to the ringing signal and causes
transistors 112 to turn on and generate a logic 0
signal on lead Rl. Microcomputer 10 detects and
validates this logic 0 signal and outputs a lamp ~lash
signal (1 pulse per second, 50% duty cycle) to lead
Ll via gate 14. Microcomputer 10 also applies a
warble tone to lead W and enables gate 15 via lead
Cl thereby applying the warble tone to common audible
lead CAl. Upon operation of a line pickup key asso-
ciated with station 1 an ~-lead signal will be applied
to microcomputer 10 via gate 13. Microcomputer 10
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responds to the A-lead signal by outputting a steady
lamp signal to lead Ll via gate 14. Microcomputer
10 also removes the common audible enable signal from
lead Cl and the warble tone from lead W thereby re-
moving the common audible signal from lead CAl. Line
relay 107 operates in response to connection of the
tip and ring leads, Tl (STA) and Rl (STA), to station
1. Line relay contacts 107A close in response to
operation of relay 107 and apply a minus 24 volt
signal (logic 0 to microcomputer 10 to indicate opera-
tion of the line relay.
The operation of the microcomputer controlled
key telephone line circuit is the same, as above de-
scribed, for placing an outgoing call. In this case
however ringing current is not initially detected
and microcomputer 10 is in a scanning mode and ini-
tially responds to operation of a line pickup key
associated with station one, as detected on the Al
lead via gate 13.
If the hold button associated with station
1 is depressed it will initially cause the Al lead
to become deactivated. Microcomputer 10 will detect
this state of the Al lead via gate 13 and apply a
lamp wink signal to lead Ll via gate 14. The lamp
wink signal is a 500 millisecond signal with a 90~
duty cycle providing a 450 millisecond period during
which the lamp is on and a S0 millisecond period
during which the lamp is off.
Microcomputer 10 als~ operates in response
to deactivation of the Al lead to operate loop relay
12. Contacts 12A are closed in response to operation
of loop relay 12 thereby connecting resistor 115 in
shunt across the tip and ring leads. Resistor 115
provides a holding bridge across the tip and ring
leads to present a loop to the central office via
line 1 when complete depression of the hold key dis-
connects sl:ation 1 from the tip and ring leads.
Operation of loop relay 12 also causes contacts 12
to close thereby connecting a tone on hold source
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from microcomputer 10 to a winding of line relay 107.
Microcomputer 10 generates a continuous tone burst
for 100 milliseconds every 10 seconds to provide a
tone on hold signal. Since this signal is applied
to a winding of loop relay 12 it is coupled on to
the tip and ring winding of relay 12 thereby providing
the tone on hold signal to line 1. If the hold condi~
tion of station 1 is removed by depressing a line
pickup key, microcomputer 10 will detect the presence
of an active A-lead via a gate 13 and release relay
12 therey removing the bridge resistor from the tip
and ring leads and also disconnecting the tone on
hold lead from line relay 107. Microcomputer 10 will
further remove the lamp link signal from lead Ll and
apply a steady lamp signal via gate 14. Also, if
a call on-hold is abandoned by the held party, micro-
computer 10 will detect the absence of loop current
and after 450 milliseconds will remove the hold bridge
thus dropping the connection.
Microcomputer 10 has 5 modes of operation,
idle (on-hook), a lead timing, off-hook, on-hold,
and ringing. During the idle mode microcomputer 10
scans A leads, Al and A2, and ringing leads, Rl and
R2. Microcomputer 10 scans these leads once every
10 milliseconds and upon detection of an active A-
lead it will operate in the A-lead timing mode while
upon detection of an active ringing lead it will
operate in the ringing mode. From the ringing mode
of operation, the idle mode can be entered if the
ringing signal was invalid and the A-lead timing mode
can be entered if an A-lead becomes active in the
ringing mode. From the A-lead timing mode the idle
mode will be entered if the active A-lead was invalid
while the off-hook mode will be entered upon detection
of a valid A-lead signal. If the A-lead becomes in-
active while in the off-hook mode of operation the
on-hold mode will be entered and if the tip and ring
leads become inactive while the A-lead is inactive
microcomputer 10 will return to the idle mode of
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operation. If the A-lead becomes active in the on-
hold mode of operation microcomputer 10 will return
to the A-lead timing mode of operation.
A detailed description of these five modes
of operation follows. The idle mode of operation
is a supervisory state during which ringing leads
and A-leads are continuously scanned once every 10
milliseconds to detect an incoming call via the ring-
ing leads and origination of an outgoing call via
the A-leads. As stated previously upon detection
of an active A-lead representing an outgoing call
origination, the A-lead timing mode will be entered
while upon detection oE an active ringing lead repre-
senting an incoming call the ringing mode of operation
will be entered.
In the ringing mode of operation microcom-
puter 10 will scan the active ringing lead once every
10 milliseconds and upon detection of a valid ringing
signal represented by 125 milliseconds of continuous
ringing signal microcomputer 10 will output a lamp
flash signal to lead Ll. It will also output a warble
tone to common audible lead CAl. If an invalid ring-
ing signal had been detected as represented by less
than 125 milliseconds of continuous ringing signal
microcomputer 10 will reenter the idle mode of opera-
tion. Thus the A-lead timing mode of operation is
entered via detection of an active A-lead in the idle
mode of operation in response to origination of an
outgoing call and it is also entered via detection
of an active A-lead in the ringing mode of operation.
The A-lead becomes active in either case in response
to operation of a line pickup key which is operated
either for call origination, or in response to lamp
flash and common audible tone for an incoming call. -
Xn the A-lead timing mode of operation micro-
computer 1() continuously scans the A-lead once every
10 milliseconds and upon detection of a valid A-lead
as represented by 50 milliseconds of a continuously
active A-lead, microcomputer 10 will output a steady
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lamp signal, remove the warble tone from the common
audible lead and then enter the off-hook mode of
operation. If the A-lead had been invalid as repre-
sented by les~ than 50 milliseconds of a continuously
active A-lead signal microcomputer 10 will reenter
the idle state.
In the off-hook mode of operation microcom-
puter 10 will continuously scan the A-lead and upon
detection of an inactive A-lead for greater than 50
milliseconds while the tip and ring leads remain
active, microcomputer 10 will enter the on-hold mode
of operation. If the call becomes abandoned as repre-
sented by the tip and ring leads becoming inactive
within 50 milliseconds of the A-lead becoming inactive
microcomputer 10 will reenter the idle mode of operation.
In the on-hold mode of operation if the
A lead becomes active again for 20 milliseconds micro-
computer 10 will reenter the A-lead timing mode of
operation while if the tip and ring leads become in-
active for 450 mllliseconds the microcomputer willreenter the idle mode of operation since the call
was abandoned.
The microcomputer controlled key telephone
line circuit of the present invention is controlled
by microcomputer 10 in accordance with a program
stored in its memory. A representative example of
a microcomputer which can be adapted to the present
invention is the Intel 8048. Microcomputers are well
known and other comparable microcomputers could be
adapted to the pxesent invention by those skilled
in the art.
The microcomputer controlled key telephone
line circuit of the present invention thus performs
the standard key telephone functions of line pickup,
hold detection, ringing current detection, lamp illu-
mination and tone signalling under control of a micro
computer. While the microcomputer controlled key
telephone line circuit of the present invention can
be connected to numerous stations only 2 stations
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- were shown in the preferred embodiment since micro-
computer 10 is shown connected to only 2 lines.
Additional lines and stations could be connected to
microprocessor 10 since the capacity of such a system
can be increased through use of microcomputers with
additional processing capability.
It will be obvious to those skilled in the
art that numerous modificatic>ns of the present inven-
tion can be made without departing from the spirit
of the invention which shall be limited only by the
scope of the claims appended hereto.
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