United States Patent [191
`Huizinga et al.
`
`[11]
`[45]
`
`4,046,972
`Sept. 6, 1977
`
`[54] KEY TELEPHONE STATION SET CIRCUIT
`[75] Inventors: Donald Dean Huizinga, Indianapolis;
`Edward William Underhill,
`Knightstown; James Arthur
`Whitcomb, Indianapolis, all of Ind.
`Bell Telephone Laboratories,
`Incorporated, Murray Hill, NJ.
`[21] Appl.No.: 735,991
`[22] Filed:
`Oct. 27, 1976
`
`[73] Assignee:
`
`[51] Int. Cl.2 ............................................. .. H04Q 5/ 18
`[52] US. Cl. .................................. .. 179/99; 179/84 L;
`179/ 84 T
`[58] Field of Search .................... .. 179/99, 18 J, 18 F,
`179/18 FA, 84 T, 84 L
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`8/1964 Boehly et a1. .................... .. 179/84 T
`3,146,314
`5/1968 Anderson et a1. ..
`3,385,935
`7/1970 Anderson et a1. ................... .. 179/ 18
`3,519,757
`3,763,326 10/1973 Murtu et a1. ......................... .. 179/99
`3,843,845 10/1974 Ridley .................................. .. 179/99
`
`3,906,168
`3,935,396
`3,946,146
`
`9/1975 McEdwen ........................... .. 179/99
`1/1976
`Barsellotti. et a1.
`179/99
`3/1976 Brown et a1. . . . . .
`. . . .. 179/99
`
`3,973,085
`
`8/1976 Shiff . . . . . . . . . . . . . .
`
`. . . .. 179/99
`
`3,991,282 11/1976
`
`Feil ....................................... .. 179/99
`
`Primary Examiner—Kathleen H. Claffy
`Assistant Examiner—Gera1d L. Brigance ‘
`Attorney, Agent, or Firm-John W. Fisher
`
`ABSTRACT
`[57]
`An electronic key telephone station set includes a plu
`rality of nonlocking line selection buttons. Adjacent
`each button is a pair of light emitting diode lamps, one
`for indicating which line selection button has been actu
`at'ed and one for indicating which ones of other lines
`having an appearance on the station set are in use. Digi
`tal data coupled to and from the station set control the
`activation of the indicating lamps as well as the type of
`alerting signal generated to indicate an incoming call.
`Numerous other features may be advantageously imple
`mented under data stream control.
`
`16 Claims, 15 Drawing Figures
`
`RUCKUS Ex 1009-pg. 1
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`

`

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`U.S. Patent—sept. 6, 1977 Sheet | of 12 4,046,972
`
`
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`
`
`Fig.|
`
`116
`
`PBX15-1
`
`113
`
`
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`CONNECTION
`
`STATIONINTERFACE
`
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`US. Patent Sept. 6, 1977
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`Sheet 2 of 12
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`4,046,972
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`RUCKUS Ex 1009-pg. 3
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`U.S. Patent Sept. 6, 1977
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`U.S. Patent Sept. 6, 1977
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`US. Patent Sept. 6, 1977
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`RUCKUS Ex 1009-pg. 11
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`U.S. Patent
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`Sept. 6, 1977
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`4,046,972
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`U.S. Patent
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`Sept. 6, 1977
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`Sheet 12 of 12
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`4,046,972
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`

`

`1
`
`4,046,972
`
`KEY TELEPHONE STATION SET CIRCUIT
`
`25
`
`30
`
`2
`SUMMARY OF THE INVENTION
`The foregoing and other objects of the invention are
`realized in an illustrative embodiment of a key tele
`phone station set circuit which includes apparatus for
`selecting one of a plurality of apparent telephone lines
`having an appearance at the station set. Circuits, respon
`sive to the selecting apparatus, produce digital data
`indicating which of the apparent telephone lines is se
`lected. Additional circuits, which are responsive to
`digital data transmitted to the station set, produce an
`indication of which one of the apparent telephone lines
`is selected and which ones of the apparent telephone
`lines are in an operational mode at other station sets
`having in common the plurality of apparent lines. Other
`circuits, which are also responsive to the digital data
`transmitted to the station set, control the volume and
`the frequency of oscillation of an alerting signal indicat
`ing an incoming call to the station set.
`Accordingly, it is one feature of the present invention
`that ringer volume and pitch are selectable under data
`stream control.
`Another feature is that power to drive the station set
`circuits is phantomly coupled to the station set on the
`control signal leads.
`A further feature of the present invention is that the
`station set circuits include a recall key for signaling an
`operator via the data stream thereby circumventing the
`problems of a dropped connection resulting from
`switchhook ?ash operator recall.
`Still another feature is that implementation of addi
`tional or special customer service features can be advan
`tageously effected under control of the data stream as
`contrasted with wiring changes.
`Yet a further feature of the present invention is that
`large scale integrated circuit technology is employed
`thereby enabling the key telephone station set circuits to
`be driven from a remote power source.
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to telephone station set circuits
`and, in particular, to circuits responsive to digital con
`trol signals for implementing key telephone functions at
`the station set.
`2. Description of the Prior Art
`Since the advent of key telephone systems several
`years ago, there has been an increasing demand that
`more and more service features be made available to the
`customer. Implementation of these additional features,
`such as call hold, operator recall, and the like, has gen
`erally required additional circuits within the station set
`itself as well as additional lines between the station set
`and a centrally located controller. At some point both
`size and cost considerations have rendered this method
`of implementation prohibitive. For example, it was not
`uncommon to have as many as 25 pairs of lines connect
`ing the station set to the controller. With the frequent
`shift of personnel utilizing key telephone apparatus, the
`time and expense involved to effect a relocation has
`become excessive.
`To circumvent these problems, the recent trend has
`been toward implementation of key telephone service
`features by means of signal multiplexing techniques.
`Multiplexing numerous signals for transmission over a
`given conductor pair has permitted a substantial reduc
`tion in the number of pairs which must be utilized for
`interconnection. Although this approach has alleviated
`to some extent the cost and space problems, it has been
`less than totally successful. As before, the addition of
`35
`other customer service features has required modi?ca
`tions and changes in the circuits.
`With the addition of other features, the amount of
`power required to drive these circuits has greatly in
`creased. In many applications it is desirable to have the
`telephone system totally divorced from the commercial
`power system. For such applications many of the re
`vised system designs have been found unsuitable. Other
`system designs, speci?cally directed toward operation
`on telephone system supplied power, have not proved
`successful because of excessive power drain caused by
`the numerous added features.
`Accordingly, it is one object of the present invention‘
`to reduce the number of signal leads into and out of the
`station set which, in turn, facilitates concentration of the
`number of leads into a cross connection network.
`Another object is to implement special customer ser
`vice features by data stream control.
`A further object of the present invention is to utilize
`large scale integrated circuit technology to reduce the
`cost and size of the circuits, to decrease the amount of
`power required to drive the circuits, to improve overall
`circuit reliability, and to reduce the number of lumped
`element components required.
`Still another object is to simplify key design and
`thereby make it more reliable by incorporating a single
`contact, nonlocking button in conjunction with a pair of
`light emitting diode lamps, one indicating the button-in
`use status and the other indicating line status.
`Yet a further object of the present invention is to use
`a direct drive for the light emitting diodes thereby re
`ducing the number of components required and the
`amount of power supply noise.
`
`45
`
`40
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The aforementioned objects and features of the inven
`tion, as well as other objects and features, will be better
`understood upon a consideration of the following de
`tailed description and the appended claims taken in
`conjunction with the attached drawings of an illustra~
`tive embodiment in which:
`FIG. 1 is a simpli?ed block diagram showing the
`interconnections between the station set and other cen
`trally located apparatus;
`FIG. 2 illustrates the physical design of the station set;
`FIG. 3 is a simpli?ed block diagram of the circuits
`within the station set;
`FIG. 4 illustrates the circuit for receiving digital data
`at the station set and for transmitting digital data from
`the station set;
`FIG. 5 when FIGS. 5a. 5b and 5c are arranged as
`_ shown in FIG. 5a’, is a schematic circuit diagram illus
`trating the data decoding and storage elements and the
`dual volume, dual pitch tone ringer circuit;
`FIG. 6 illustrates the light emitting diode lamp circuit
`and the technique utilized to increase the number of
`keys with lamps on the station set;
`FIG. 7, when FIGS. 70 and 7b are arranged as shown
`in FIG. 70,’ illustrates the light emitting diode lamp
`driver circuits; and
`FIG. 8, when FIGS. 8a and 8b are arranged as shown
`in FIG. 8c, is a timing diagram.
`
`55
`
`65
`
`RUCKUS Ex 1009-pg. 14
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`4,046,972
`
`20
`
`25
`
`3
`DETAILED DESCRIPTION
`1. Overview of System Operation
`The simpli?ed block diagram of FIG. 1 illustrates the
`interconnections among all major components to effect
`key telephone system operation. Speci?cally, there is
`shown a number of key telephone station sets desig
`nated 110-1 through 110-n. Each of the station sets 110
`is connected to a PBX 112 by a two-wire talking path
`designated T and R. In particular,‘ station set 110-1 is
`connected to PBX 112 by leads T1 and R1 and station
`set 110n is connected via leads Tn and Rn.
`Data is transmitted from station sets 110 via leads 121
`to a station interface controller 111. correspondingly,
`data from interface controller 111 is transmitted via
`leads 122 to station sets 110. The exchange of data be
`tween interface controller 11 and cross-connection net
`work 113, to establish a path through network 113, is
`effected through common control network 114. Once a
`path through network 113 is established, a connection
`to central of?ce 116 is completed via one of line circuits
`115-1 through 115m and one of lines L1 through Lm.
`2. Brief Physical Description of Station Set
`Station set 110, as shown in FIG. 2,-includes housing
`201 and hand set 202 which is interconnected with cir
`cuits in station set 110 by cord 203. On a top surface of
`housing 201 is face plate 205. Along the right-hand side
`of face plate 205 there is mounted a plurality of non
`locking line selection pushbuttons 210. Adjacent to
`each of buttons 210 are a pair of light emitting diode
`(LED) lamps 211 and 212. LED 211 provides a visual
`indication of which ones of the lines having an appear
`ance on station set 110 are in use at other locations.
`LED 212 provides a visual display as to which one of
`buttons 210 has been selected by a user.
`It should be noted at this point that even though ten
`lines are shown as having an appearance on station set
`110, only a single talking pair T and R connect the set to
`PBX 112, shown in FIG. 1. It should be noted also that
`station sets 110 may be advantageously con?gured to
`permit ten, twenty, thirty or more lines to have an ap
`pearance on the set. However, even for these con?gura
`tions, only a single talking pair T and R interconnect set
`110 with PBX 112.
`To complete this brief physical description of station
`set 110, attention should be directed to the left central
`region of face plate 205 at which is located pushbutton
`dial 213. Near the lower left-hand corner of face plate
`205 is an operator recall key 214.
`I
`3. Brief Description of Station Set Circuits
`The circuits within station set 110 are shown in the
`simpli?ed block diagram of FIG. 3. Many of the cir
`cuits, such as handset 202, dial 213, switchhook 310, and
`network 311 are standard telephone components.
`Switchhook 310 is modi?ed to have an extra lead 309
`for transmitting data to logic circuit 316. Otherwise
`there are no other changes. Consequently, little else
`need be said about these components. Power supply 312
`is designed to receive power phantomed .on data lines
`121 and 122 and convert the received power into the
`requisite voltage for operating logic circuit 316 and key
`assembly 317. However, with regard to the remaining
`components, which are shown in bold face outlines, the
`bulk of the following discussion will concentrate on
`them.
`
`4
`In particular, data to station set 110 arrives via leads
`122 and is conditioned in transmitter/receiver circuit
`315. Since power is supplied over the data lines, trans
`mitter/ receiver circuit 315 separates the data from the
`power. The power signal is routed to power supply 312
`which generates the requisite voltages needed to oper
`ate logic circuit 316.
`Incoming data, following conditioning by transmit
`ter/receiver circuit 315,-‘ are routed to logic circuit 316
`over a number of signal paths illustrated collectively as
`leads 320. Logic circuit 316 operates upon the data,
`referred to as lamp data, to initiate the alerting function
`effected by tone ringer 318. Potentiometer 319 permits
`manual control of the volume of the alerting signal
`produced by tone ringer 318. Also, signals to light the
`LED lamps are developed and routed to key assembly
`317 via leads 321.
`'
`Actions taken by the user with respect to the buttons
`210 produce signals which are coupled from key assem
`bly 317 back to logic circuit 316. These signals are fur
`ther manipulated by logic circuit 316 and are then cou
`pled to transmitter/receiver circuit 315. After condi
`tioning, the signals are transmitted to interface control
`ler 111.
`4. General Description of Station Set Operation
`In operation, data from interface controller 111 regu
`lates ringer and LED lamp actuation, volume, and
`voice signaling if the latter is to be provided as one of
`the customer service features in station set 110. Suffi
`cient data is sent from interface controller 111 to service
`all LED lamps 211 and 212 in station set 110 regardless
`of the number of apparent lines having an appearance at
`the set. The data referred to above is sent to each station
`set 110, one set at a time, approximately every 25 milli
`seconds. Hence, interface controller 111 completes a
`scan of all station sets 110 in approximately 25 millisec
`onds. The actual length of a data word coupled to sta
`tion set 110 depends upon the number of buttons 210
`and LED lamps 211 and 212 provided on the set, the
`number of features to be implemented, and the amount
`of overhead data manipulation that must be effected.
`Upon receipt of data by station set 110, return data is
`generated to indicate the status of the switchhook and
`the status of all buttons on the set, whether operated or
`not. Keeping in mind that numerous custom calling
`features such as call forwarding, voice signaling,
`handsfree answer and call hold among others can be
`advantageously implemented under data stream con
`trol, operation of station set 110 will become clear upon
`consideration of the two major types of calls that may
`occur. The types of calls to be considered are outgoing
`calls and incoming calls.
`4.1 Outgoing Call
`The ?rst step undertaken by a user in placing an out
`going call is to lift handset 202 thereby causing station
`set 110 to go into an off-hook state. Recalling that data
`is transferred between station set 110 and interface con
`troller 111 approximately every 25 milliseconds, station
`set 110 being in an off-hook state causes the ?rst bit in
`the data word transmitted to interface controller 111 to
`go to a high logic level. A typical de?nition of a data
`word from station set 110 is presented in Table 1 as
`button data period. Similarly, a de?nition of a data
`‘word to station set 110 is presented in Table 1 as lamp
`65
`data period. Once the switchhook bit goes high, it con
`tinues to be transmitted as such so long as station set 110
`remains in the off-hook state.
`
`35
`
`40
`
`45
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`4,046,972
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`EKT MODE
`
`Lamp Data Controlled
`Period Function
`
`TABLE 1
`LAMP AND BUTTON DATA DEFINITIONS
`Controlled State
`"Zero" “One"
`Lamp Lamp
`State
`State
`
`Button
`’
`Data
`Period Controlling Function
`
`Controlling State
`“Zero"
`"One"
`Button
`Button
`State
`State
`
`4
`
`l
`
`2
`1 } (Rmger )
`2
`ON/OFF
`750 Hz 1500 Hz 3
`3 Ringer Tone
`4 Ringer Volume Full
`Reduced 4
`5 Voice Signaling OFF ON
`5
`6 Ll LED
`OFF ON
`6
`7 ll LED
`OFF ON
`‘NT
`8 L2 LED
`OFF ON
`7
`9 12 LED
`OFF ON
`NT
`10 L3 LED
`OFF ON
`8
`11 I3 LED
`OFF ON
`NT
`12 L4 LED
`OFF ON
`9
`13 I4 LED
`OFF ON
`NT
`14 L5 LED
`OFF ON
`10
`15 I5 LED
`OFF ON
`NT
`16 L6 LED
`OFF ON
`ll
`17 16 LED
`OFF ON
`NT
`18 L7 LED
`OFF ON
`12
`19 I7 LED
`OFF ON
`NT
`20 L8 LED
`OFF ON
`13
`21 I8 LED
`OFF ON
`NT
`22 L9 LED
`OFF ON
`14
`23 I9 LED
`OFF ON
`NT
`24 L10 LED
`OFF ON
`15
`25 I10 LED
`OFF ON
`NT
`
`# = "0“ only if all subsequent button data bits “0".
`'= No Transmitted Bit.
`
`switchhook
`
`Button Common
`Data Stream Dialing
`Direct Sta. Selection
`Recall
`Button 1
`
`Button 2
`
`Button 3
`
`Button 4
`
`Button 5
`
`Button 6
`'
`Button 7
`
`Button 8
`
`Button 9
`
`On-Hood Off-Hook
`
`#
`Open
`Open
`Open
`Open
`'
`Open
`
`Open
`1
`Open
`'
`Open
`
`#
`Closed
`Closed
`Closed
`Closed
`
`Closed
`
`Closed
`
`Closed
`
`Closed
`
`Open
`
`Closed
`
`Open
`
`Closed
`
`Open
`
`Closed
`
`Open
`
`Closed
`
`Button 10
`
`Open
`
`Closed
`
`30
`
`35
`
`corresponding to the line being rung. The rate of turn
`on and turn-off is also under data stream control.
`Until there ‘is an answer, the data back to interface
`controller 111 is unchanged. However, once station set
`110 is put into an off-hook state by an answering user,
`the switchhook bit back to interface controller 111 goes
`high.
`For purposes of the following discussion, assume line
`1 is being rung. Upon lifting handset 202, the user
`presses button 210 next to line ll. The ?ashing of lamp
`L1 now goes to a steady-on state and lamp I1 comes on
`and goes to a steady-on state. At the same time tone
`ringing is terminated; tip and ring leads, T and R, are
`energized; and the call connectionris completed. Every
`thing remains the above-de?ned state until station set
`110 is returned to an" on-hook state at which time the L1
`lamp is extinguished.
`It should be somewhat apparent from the above dis
`cussion that the ?rst several bits in each data word are
`devoted to overhead type functions and the remaining
`bits are devoted to lamp and button functions. A typical
`example of each bit function is set out in Table l.
`5. Transmitter/Receiver Circuit
`Data transmitted in either direction between station
`set 110 and interface controller 111 is in a bipolar for
`mat. Consequently, the primary function of transmit
`ter/ receiver circuit 315, shown in more detail in FIG. 4,
`is to convert the bipolar pulses to two unipolar pulses
`upon reception or vice versa for transmission.
`Consider first receiver operation. Transformer T201
`. in conjunction with transistors Q201 and Q202 and
`resistor R201 convert bipolar signals appearing on leads
`LR and LT into the unipolar signals. For example, if a
`bipolar 0 is received, the collector of transistor Q202
`goes low ?rst, followed by the collector of transistor
`Q20]. Hence, two unipolar pulses are developed on
`leads R0 and‘ R1 into logic circuit 316. Waveforms for
`these signals are shown on the timing chart of FIG. 8.
`For a bipolar l the waveforms are merely the inverse of
`those just described.
`
`At this point the user presses a key button to select a
`line. For present purposes, assume button 1 is depressed.
`Consequently, bits 2 and 6 from station set 110 to inter
`face controller 111 go high. In the data word returned
`to station set 110, bits 6 and 7 are high causing line 1
`lamps L1 and I1 to light. At the same time tip and ring
`leads, T and R, are energized or connected to set 110
`and dial tone is returned. Thereupon the user dials the
`desired number. It should be noted that any other sta
`tion sets 110 with line 1 appearing thereon receive data
`from interface controller 111 to light their L1 lamps.
`When the user hangs up, the switchhook bit goes low
`and all lamps for line 1 are extinguished.
`4.2 Incoming Call
`For an incoming call, data bits are sent during the
`course of a sequential scan by interface controller 111 of
`station set 110. These bits control ringing aswell as the
`45
`lighting of lamps. Tone ringer 318, about which more
`will be said later, oscillates at either 750 Hz or 1500 Hz.
`Interface controller 111 can advantageously select’
`which of these frequencies is to be produced and also
`the interval during which it is produced. For example,
`during one scan period 750 Hz may be advantageously
`generated whereas on the next scan 1500 Hz may be
`advantageously generated. Another possibility is to turn
`one of the aforementioned frequency signals on during
`one data period and off during the next data period
`thereby producing approximately a 20 Hz modulation
`in the ringing signal. Still further it is possible to use the
`low frequency signal for indicating an outside call with
`the high frequency signal indicating an in-house call.
`Frequency selection and the ringer on/off function are
`under the control of bits 1, 2, and 3 of the lamp data
`word as shown in Table l.
`'
`Similarly, the volume of the alerting signal can be
`advantageously controlled by the data stream. For in
`stance, if bit 4 of the lamp data is low the volume is
`normal whereas if the bit is high the volume is reduced.
`During the course of the alerting function, data is also
`sent to station set 110 to turn on and off the L-lamp
`
`50
`
`55
`
`65
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`RUCKUS Ex 1009-pg. 16
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`

`

`10
`
`40
`
`7
`Resistor R203 and capacitor C202 form an RC-?lter
`to remove any high frequency and impulse noise. Simi
`larly, resistor R202 and capacitor C201 provide ?ltering
`in the circuit incorporating transistor Q201.
`With regard to transmitter operation, positive unipo
`lar signals coupled out of logic circuit 316 on leads X0
`and X1 turn on transistors Q203 and Q204, the emitters
`of which are coupled to a negative power supply via
`lead VN. These signals, as shown in the timing chart of
`FIG. 8, develop across the output of transformer T202
`the desired bipolar signal which is transmitted, in turn,
`to interface controller 111 via leads BR and BT. Timing
`for the transmitted bipolar signals is controlled by RC
`networks. Speci?cally, the ?rst transmit period is con
`trolled by capacitor C301 and resistor R301 whereas the
`second transmit period is controlled by capacitor C302
`and resistor R302.
`Resistor R207 coupled between the center taps of
`transformers T201 and T202 limits the collector current
`20
`drawn from the positive power supply. Capacitor C304
`in lead VN is used to detect the end of a data word and
`subsequently to reset all ?ip-?op shift registers in prepa
`ration for the next data word. Impedance matching to
`the line in the receive mode is effected by resistor R201
`25
`and in the transmit mode by resistor R206. Diode
`CR302 protects against static voltages on the switch
`hook lead SH.
`The remaining circuits, shown in FIG. 4, provide
`control for tone ringer 318, shown in FIG. 3. In particu
`lar, capacitor C303 and resistor R303 control the oscil
`lation period. With transistors Q301 and Q302 turned
`on, there is a short circuit between lead VN and potenti
`ometer 319 shown in FIG. 3. The current ?owing be
`tween these two points drives a speaker (not shown).
`The input to transistor Q301 on lead RON provides
`on/off control for tone ringer 318. The input to transis
`tor Q302 on lead RVL provides volume control. Thus,
`with transistor Q302 off and transistor Q301 on, the
`current is limited by resistor R305 to give the low vol
`ume condition for tone ringer 318.
`When transistor Q301 is turned off, ringing ceases.
`However, current brie?y flows around a loop contain
`ing diode CR301 until the current due to speaker induc
`tance dissipates. Diodes CR301 is a flyback diode which
`prevents any overvoltage in the negative direction.
`It should be noted that leads TB, RL, CLK, SR5, DI,
`and DL coupled to logic circuit 316 in FIG. 4 are leads
`321 shown in FIG. 3.
`Also, it should be noted that lead EKT couples to a
`switch (not shown) which is used to select the mode of
`operation of station set 110. Three modes of operation
`are available. In the ?rst mode station set 110 functions
`as a multibutton electronic telephone. In the second
`mode it functions as an electronic custom calling tele
`phone. The third mode of operation is a mix between
`the ?rst two modes, that is, station set 110 is a multibut
`ton telephone with a number of custom calling features
`available.
`6. Logic Circuit
`Logic circuit 316, as shown in FIGS. 50, 5b, and 5c,
`when arranged in accordance with FIG. 5d, includes
`several major subcircuits such as input latch 511, local
`clock 512, reset circuit 514, storage circuit 516, shift
`register 518, input gating circuit 520, and mode selector
`circuit 521. Each of these circuits will be considered in
`more detail in the following subsections.
`6.1 Reset Circuit
`
`4,046,972
`8
`Reset circuit 514 performs two sets of functions. The
`?rst set of functions includes initialization of shift regis
`ter 518, the resetting of all ?ip-?ops in storage circuit
`516, and generation of an RL pulse, as shown in the
`timing chart of FIG. 8, to turn off all LEDs in key
`assembly 317. The second function is to restore shift
`register 518 to its initial counting position following the
`reception of a complete data word from interface con
`troller 111.
`To implement the ?rst set of functions, power-up
`reset circuit 513 develops a low logic signal and holds
`this signal on its output lead PUP as power is ?rst ap
`plied. With a low on lead PUP, ?ip-?op FF1 in storage
`circuit 516 is set and flip-?ops FF2 through FF5 in the
`same circuit are reset. In addition, NAND gate GR2
`and inverter R are actuated to produce a low on lead R
`which sets ?ip-?ops SR1 and resets ?ip-?ops SR2
`through SR6 in shift register 518. The low on lead R
`also sets ?ip-?op TGAl and resets ?ip-?ops FFAl and
`TA2 in mode selector circuit 521. Simultaneously, a low
`via NAND gate DI and inverter DI appears on lead DI,
`and ?ip-?op FFRl in input/output circuit 510 is reset
`via inverters I10 and Ill and capacitor C10 forcing lead
`DL low. This set of circuit changes puts logic circuit
`316 in a rest state between data words so it is ready to
`accept the ?rst bit of the ?rst data word.
`When the power supply voltage exceeds about 4.8
`volts, the signal on lead PUP goes high. This signal
`removes the set or reset signals to ?ip-?ops FF1
`through FF5 in storage circuit 516._I_r_1 addition, invert
`ers IR4 and RL and NOR gate RL in input/output
`circuit 510 are actuated to produce a low on lead RL. In
`effect, power~up reset circuit 513 prevents excessive
`current drain when station set 110 is ?rst turned on
`since all LEDs are held in an off state during this inter
`val.
`The remaining portion of reset circuit 514 produces a
`negative voltage on capacitor C304 in lead C of trans
`mitter/receiver circuit 315 shown in FIG. 4. This volt
`age is held below a threshold so long as additional
`pulses are received within a data word. At the end of
`the word, the charge decays, the voltage goes above
`threshold, and a reset pulse is generated to reinitialize
`logic circuit 316 and key assembly 317. The effect of
`this operation is to restore the pointer function effected
`by shift register 518 to an initial position.
`As a further part of the initialization effected by reset
`circuit 514, the setting of ?ip-?op FF1 and the resetting
`of ?ip-?op FF2 in storage circuit 516 prevents tone
`ringer 318 from going on when station set 110 ?rst
`receives power. In fact, tone ringer 318 remains turned
`off so long as the output of NOR gate GDI is low. This
`result obtains because with this level applied to transis
`tor QPl oscillation is inhibited.
`Also, a low output from NOR gate GDl resets ?ip
`?ops TSA, TSB, and TSC which, in turn, puts divide
`by-two and divide-by-three circuits in tone ringer 318 in
`a proper state to initiate their counting sequences. The
`divide-by-two circuit is used in the production of the
`low frequency tone and is by-passed during the produc
`tion of the high frequency tone. The divide-by-three
`circuit produces a one-third duty cycle thereby enhanc
`ing the harmonic content in the sound produced by tone
`ringer 318.
`6.2 Local Clock
`Local clock 512 takes the leading edge of each bit
`transmitted to logic circuit 316 and sets and adjusts the
`timing for each bit to be returned to interface controller
`
`50
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`55
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`65
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`

`4,046,972
`9
`111. Pulses P1 and P2, as shown in the timing chart of
`FIG. 8, trigger transmit gating circuit 519 to return data
`from station set 110 to interface controller 111 on a
`delayed bit-by-bit basis under the control of shift regis
`ter 518.
`Included in local clock 512 are a pair of delay sections
`DP] and DP2. These delay sections, when a high ap
`pears on their output, remain high for a time interval
`controlled by an external RC network. After this time
`interval, the output changes, and the delay section func
`tions similar to an inverter. However, when the input
`returns to a low, the output of the delay section goes
`high almost instantaneously. Inverter TGR ensures a
`fast reset when delay section DPl goes low.
`A voltage, developed across resistors R5 and R6 and
`applied at the point designated Vmfin local clock 512,
`establishes the trigger point where the delay produced
`by the RC network causes this change of state.
`With a low received on lead R0, NAND gate TRG is ~
`forced high and the output of delay section DPl is held
`20
`high for the preselected delay interval after which it
`changes state. This delay interval is ?xed by resistor
`R301 and capacitor C301 and is typically on the order
`of one microsecond.