The present invention relates in general to paging systems, and is particularly directed to a paging system controller which is accessible from a plurality of input devices, such as an attendant's position, a telephone interface, telephone light bell, programmable switch devices and digital data communications devices, and is programmed to respond to paging request activity sourced from such accessing devices, and to establish a paging connection to and perform prescribed audio/visual output paging signal functions with respect to one or more paging zones served by the system.

Paging systems have historically involved real time audio paging in (relatively low background noise) office environments, and the generation of digitized voice messages (typically scrolled across a pixel matrix display) is high ambient noise environments, such as an industrial production line facility. In order to provide emergency information, various types of warning devices have been installed in such environments for emitting alert tones (sirens) or prerecorded ( 'canned' ) messages over the paging a system.

A fundamental shortcoming of such conventional paging systems has been their inability to provide either adequate normal paging or emergency information to the variety of personnel who can be expected to be present in both low noise and high noise environment, particularly now that the 1990 Americans with Disabilities Act (ADA) requires most office and industrial facilities to provide access and freedom of movement to physically impaired individuals. Although the ADA

effectively mandates the freedom of access and movement to all individuals, it does not address the need for visual messaging for either standard or emergency page announcements for the hearing-impaired, or audible page announcements for the visually impaired.

In accordance with the present invention, such shortcomings of conventional paging systems and their associated control mechanisms are remedied by a new and improved paging system controller, which is accessible from a plurality of input devices, such as an attendant's position, a telephone interface, telephone night hell, programmable switch devices and digital data communications devices, and is user- programmable to respond to signalling activity sourced from such accessing devices to establish a paging connection to and perform prescribed audio/visual output paging signal functions with respect to one or a plurality of paging zones served by the system.

The output paging signal functions include, but are not limited to, the transmission of audio tone and voice paging signals via an audio signal path from a paging source to one or more (controllably energized) paging loudspeaker amplifiers, the generation of one or more alert tones to a paging zone, talkback audio signalling from the paging zone to a telephone interface, the playback of prerecorded (audio/visual) messages om either or both of audio output (e.g. loudspeaker) and visual output (e.g. silent radio) devices.

Since the paging system controller of the present invention is accessible from a plurality of inputs and is programmable to provide single or multiple output signalling capability, the respective access inputs to which it responds are given user- programmable priorities of access permission, with a higher priority access input always being given preference over a lower

priority access input. A programmable access priority table, which may be customized by the user to assign respectively different access priority levels to respectively different classes or types of input access is stored in memory employed by the control system's processor.

As a non-limiting example, the highest priority level may be associated with access by an attendant. A second level of access priority may be assigned to a first set of paging zone switch inputs, while telephone interface access may be assigned to a third highest priority level. A second set of paging zone switch inputs may be given a fourth highest priority level, and a night bell given a fifth highest priority level. In the absence of an access input from any of these priority levels, the controller may default to a prescribed signal source, such as music or news broadcast, for providing 'background' audio to the paging zones served by the system.

The paging system controller draws its power from a separate amplifier subsystem associated with the audio speakers of the paging system, by means of a power interface unit containing DC-DC converter circuitry, which converts voltage outputs provided by a paging speaker amplifier subsystem andl5 translates these voltages to values required by the components of the controller. The drive voltage for operating paging speaker amplifiers is controllably switched, under supervisory processor control, to whatever zone output device is to generate a paging/tone output.

For attendant access, audio/paging signals, such as may be sourced from an operator's headset microphone of an accessing attendant's position, are coupled via an input connector to an controlled audio signal path through which tones and audio signals are conveyed. The input connector also has an attendant access control port through which a supervisory microcontroller

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device through one or more paging speakers, or the activation of visual display playback unit to drive a message display device, such as a silent radio.

Thus, similar to an attendant access, through programming of the paging routine resident in processor memory, a zone switch input may be employed to instruct the microcontroller to output prescribed alerting tone signals, which are coupled to a specified one or more of output zone ports, so that an input type-initiated alerting tone may be coupled to one or more specified amplified speakers or a specified group of speakers. The zone inputs may also be used to instruct the processor to assert an output on one or more of the switch units to controllably activate a zone utility device, such as a warning strobe light or prerecorded visual and/or message the operation of which is responsive to the closure of the zone switch contacts. Also, through programming, the processor may transmit a preprogrammed (audio/visual) page signalling protocol to one or more virtual digital port addresses distributed on an associated data communications bus. Any audio/visual output device addressed either individually or globally by this protocol will respond by generating a prescribed audio/visual message.

Additional functionality of the paging control system of the present invention is given to a calling party telephone access, and may include any one of four modes; Dloop start; 2) ground start; 3) station; and 4) dry loop. Telephone interface access is by way of a modular jack having respective tip and ring terminals which are coupled to the tip and ring lines of a telephone line, a ground terminal which is coupled to system ground, and a dry loop terminal, which is coupled to a dry lδop detection circuit. The jack ports are coupled through a user- presettable mode switch to a telephone interface signalling

translates a multiple digit code (e.g. a three or four extension code or a four digit direct dial code) into the zone number in which the called party's telephone set is located. The microcontroller accesses the translating zone map in memory and outputs paging signals to the appropriate zone in which the called party is located. Thus, in an office environment, where plural office personnel are located in a given zone, the extension numbers of their respective desk phones are mapped to the same zone number of their shared zone. The calling party needs only know the extension number of the desk phone to effect a page.

To allow for the control system of the invention to be expanded to one or more zones beyond the. zone capacity of the zone output latching driver stages, one or more zone expansion units, each of which contains plural zone switch units, may be connected in a daisy-chain interconnect configuration, via a5 zone expansion port coupled to a processor I ² C bus. The zone expansion unit port includes digital signal conditioning circuits, which are operative to interface a digital signalling clock and digital data signals between addressed latching zone switching circuits of one or more zone expansion units, and clock and data portions of the 1 ² C bus. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a simplified block diagram illustration of a paging system controller in accordance with the present invention;

Figure 2 schematically illustrates the circuit configuration of a power interface unit employed in the paging system controller of Figure 1; Figure 3 schematically illustrates the circuit configuration of a zone expansion interface unit;

Figures 4A and 4B, taken together, schematically

^' illustrate the circuit configurations of attendant access and telephone interface audio path signal processing circuits, and the tone generator circuitry employed in the bidirectional audio signal interface unit of Figure 1; Figures 5A and 5B taken together schematically illustrate the circuit configurations of paging, tone and talkback path signal processing circuits of the bidirectional audio signal interface unit of Figure 1;

Figures 6A and 6B taken together schematically illustrate the circuit configurations of DTMF decoder, night5 bell detection, control processor, multi-port and digital data port connections employed in the paging system controller of Figure 1;

Figure 7 schematically illustrates the circuit configuration of a programmable zone switch unit;

Figure 8A schematically illustrates the circuit configuration of a programmable zone expansion switch unit;

Figure 8B diagrammatically illustrates a respective zone expansion unit; Figures 9 - 12 are a port assignment table associated wish the operation of the page controller of Figure 1. DETAILED DESCRIPTION

Before describing in detail the particular improved paging system controller architecture in accordance with the present invention, it should be observed that, for the most part, th§0 present invention resides primarily in a novel structural combination of conventional signal processing and communication circuits and components and not in the particular detailed configurations thereof. Accordingly, the structure, control and arrangement of these conventional circuits anS.5 components have been illustrated in the drawings by readily understandable block diagrams which show only those specific

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from input ports to audio paging output devices (of a paging speaker/amplifier subsystem 2SA) that are coupled to selected ones of the plurality of output ports, and to couple talkback and tone signals to selected input port connections. The bidirectional audio signal interface 3 is controlled by a supervisory processor-based control unit 4, which is operative to enable prescribed types of paging signals to be delivered to the output ports in accordance with paging access input signals supplied to the input ports. The architecture and operation of the controller will be better understood with reference to Figures 4A - 8, which diagrammatically illustrate the circuitry configuration of each of the input and output port connections, as well as the signal processing and conditioning circuitry contained within each of the bidirectional audio signal interface and its associated control unit.

As noted earlier, the paging system controller of the present invention draws its power from a separate amplifier subsystem associated with the audio speakers of the paging system. For this purpose, as shown in Figure 2, the controller includes a power interface unit 20 comprised of DC-DC converter circuitry which is operative to receive prescribed voltages customarily provided by a paging speaker amplifier unit (e.g. +15VDC and -24VDC) and translates these voltages to values required by the components of the controller. As schematically illustrated in Figure 2, the DC-DC converter circuitry includes respective DC-DC converters 22 and 23 which are coupled to a +15VpC input pin 32 of a power supply jack J2 and provide respective voltages +12VDC and -5VDC at output terminals 33 and 34, respectively.

Similarly, respective DC-DC converters 24 and 25 are coupled to a -24VDC input pin 32 of power supply jack 32 and provide

respective voltages -12VDC and -5VDC at output terminals 36 and 37, respectively. Ground (GND) is shown at jack pin 38, while +/-70VAC for paging speaker audio amplifiers are coupled between terminals 41 and 42 and associated pins of power supply jack 32.

The controller also employs a zone expansion interface unit, shown in Figure 3, which includes a pair of passive, digital signal conditioning circuits 26 and 27, which are respectively coupled to clock and data pins 44 and 45 of a zone expansion unit jack 31, and are operative to interface a digital signalling clock and digital data signals between addreised latching switching circuits of one or more zone expansion units, shown in Figures 8 and 9, to be described below, and clock and data terminals 46 and 47 which are coupled to an I ² C bus associated with the controller's internal supervisory processor, as will be described. Ground (GND) is shown at jack pin 48, while +/-70VAC for audio amplifier units employed by a zone expansion unit speaker system are coupled between terminals 51 and 52 and associated pins of zone expansion unit jack Jl . The circuitry configuration of the signal processing components of the bi-directional paging control system will now be described with reference to Figures 4A - 6A. To facilitate the an understanding of the integration and functionality of the respective components of the invention, the respective signal processing capabilities of the system will be described in association with the respective classes of service performed by the controller. As noted earlier, because the paging system of the present invention is programmable and provides for both audio (e.g. paging speaker) and visual (e.g. silent radio) output capability in any one paging zone or group of paging zones, the assignment of respective paging operations and importance of input stimuli to the system are selectable by the

user. Moreover, control inputs to the paging system of the present invention may be derived from a variety of sources, including, but not limited to, a telephone attendant access, a telephone interface, a prescribed facility input device, such as a night bell, or one or more programmable input/output devices, such as user selectable switch devices, the settings of respective ones of which are associated with prescribed signalling actions associated with one or more output devices installed by the user to define the overall functionality and communication capabilities of the pagiSg system.

Because the paging system controller of the present invention is capable of being accessed from a plurality of inputs and is intended to provide single or multiple output signalling capability, the respective access inputs to which it is intended to respond are given respective priorities of access permission, programmable by the user, so that, in the event of multiple simultaneous access inputs, a higher priority access input will always be given preference over a lower priority access input. For this purpose, the microcontroller maintains, in memory, a programmable access priority table, which may be changed (customized) by the user as desired, to assign respectively different access priority levels to respectively different classes or types of input access . The number of priority levels is not limited to any particular number, but may vary as user requirements change, the number and assignments being programmable, as noted above.

As a non-limiting example, in the description to follow, the controller will be described in association with five respectively different levels of access priority.

The first or highest priority level is associated with access by an attendant. A first set of paging zone switch inputs is

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P17 of processor 200.

The page/talkback threshold detection circuit 110 serves to cause a page audio signal on audio signal path 91 from the telephone interface (to be described) to override a taikback audio signal supplied from a telephone interface input, in dependence upon a threshold sensing level (at input 119) that is adjustable in accordance with the level of noise in the paging zone from which talkback audio is provided.

Link 112 is also coupled to one end of a MOSFET switch 114, having its gate coupled to a terminal 115, which coupled to receive a processor-sourced talk-back mute control signal TB_MUTE, and its source-drain path coupled in circuit between ground and line 112. Talk-back mute terminal 115 is also coupled to the gate of a MOSFET switch 116 ot an amplitude compression circuit 633 to which a talkback amplifier stage 140 is coupled, as will be described. When the control processor 200 asserts the TB_MUTE control signal as a logic 0 at talk-back mute terminal, these respective MOSFET switches 114 and 116 are operated to mute talk-back audio on a return path from a paging speaker and to allow paging from a paging source to the speakSr output circuitry.

Output power amplifier stage 120 is operative to drive a set of output ports 131, 132 and 133, to which amplifier circuitry of an associated paging amplifier system may be coupled. Amplifier stage 120 has a processor-control port 122 to which a control signal AMP_CD from the system's micro-controller is coupled for enabling (setting the bias voltage for) amplifier. The output of amplifier circuit 120 is not intended to serve as a direct input drive to one or more speakers, since, as pointed out previously, the control system of the present invention serves as a supervisory routing interface between one or more paging input signal sources and one or more

logic state of output port DTMF_VLD is asserted active high in response to decoder 150 detecting a valid DTMF signal. The (digital hex) contents of a valid dual tone signal are coupled via output links 151, 152, 153 and 154 to respective input ports Pll, P12, P13 and P14 of processor 200. DTMF decoder 150 has an associated clock crystal drive circuit 156, which is also coupled via link 157 to a clock drive input XTL2 of processor^ 200. Processor 200 has an additional clock input XTL1 coupled to a further crystal clock circuit 158. (Crystal clock inputs XTL1 and XTL2 provide the clock reference sources required by microcontroller 200.) System reset is provided by way of a reset port RST to which link 159 is coupled. RST link 159 is coupled to an associated watchdog timer 210, an enable (CK) input for which is coupled via link 161 from the Q4 output port of latching driver 173.

The processor-sourced control signals TONE/PAGE, AA_PHONE AND TB_PHONE, referenced previously, which are steering inputs for the audio/tone signal paths through the audio signal multiplexers, are provided on processor output ports P25, P26 and P27.

Processor 200 also has a set of bidirectional data ports P00-P07, which are coupled via a system digital data bus 160 to respective data inputs D0-D7 of each of a pair of multi-port latching output driver units 171 and 172, and to respective data outputs QO-Q7 of a multi-port input buffer driver unit 173. output latching driver 171 has a plurality (e.g. eight) of output ports Q1-Q7 coupled to output ports ZONE10UT - ZONE80UT, to which respective relay driver inputs associated with a plurality of presettable zone switch units 300 (shown in Figure 7, to be described) are coupled. Multi-port latching driver 172 has a plurality of output ports Q1-Q7 coupled to provide respective control signals which are routed to various circuit

amplifiers to which zone terminals 321 and 322 are connected.

When the sliding contacts 342, 343 are moved one position to the left from the position shown in the Figure 7, so that sliding contact 342 connects terminals 331 and 338, and sliding 343 connects terminals 332 and 339, then the switch is operative as an input device in accordance with the connection state of terminals 321 and 322. When used as an input device, the ZONEiOUT terminal 301 is held active, thereby maintaining relay winding 307 in an energized state, so that switch terminals 331 and 332 are connected to zone terminals 321 and 322, respectively, when an external contact closure (e.g. the operation of a pushbutton switch connected across terminals 321 and 322) is operative to bridge zone terminals 321 and 322, a circuit path is established between switch terminals 338 and 339, thereby asserting a low (ground) at the input to driver 341, causing its output at terminal 302 to change state (be asserted active high) . This active high assertion on ZONEi_IN terminal 301 is read by processor 200 in the course of its periodic polling of the zone inputs of zone input buffer 173.

The action taken by processor 200, in response to this active high assertion on ZONEi_IN terminal 301 will depend upon the priority level and response operation associated with the ZONEi_IN logic level. Looking now at the operation of the paging control system in response to an attendant access (assertion of a ground to input port 66) , as pointed out above, in order to initiate a page the attendant must assert a low at attendant page input port 66. Prior to an attendant asserting a page, the system may be handling a page access request of a lower level of priority, or it may be idle, in which event, the paging speakers may coupled to background audio source signals, such as music

paging zone data in accordance with the operational routine resident in processor 200.

Namely, once connected in the manner described above, the accessing attendant has the ability to instruct processor 200 to assert output signals via a specified one or more of output zone ports Z0NE10UT - ZONE70UT, to which switch units 300 are coupled, and thereby control to what output deviceslO specified actions are to occur. For example, for those switch units 300 whose switch positions have been set to their +/- 70V positions, the attendant may supply a real time audio page through an associated (70V) loudspeaker. The page may also be coupled to one or more specified amplified speakers o_t5 a specified group of speakers. The accessing attendant may also instruct the processor to assert an output on one or more of the switch units 300 (whose sliding switch contacts have been preset for this option) , so that the attendant may controllably activate a zone utility device, such as an alerting strobe light or prerecorded visual and/or message the operation of which is responsive to the closure of the zone switch contacts. In addition, as will be described in detail below, through DTMF signalling or through a serial data communications interface (e.g. RS-232 port) the attendant may instruct25 processor 200 to transmit a preprogrammed (audio/visual) page signalling protocol to one or more virtual digital port addresses distributed on an associated data communications bus. Any device addressed either individually or globally by this protocol will respond by generating a prescribed audio/visual message. For example, a paging facility served by the present invention, such as an airport terminal, may have a plurality of display terminals (e.g. silent radio message boards) distributed at a number of locations. Through the serial data communications bus, paging attendant may initiate

controllably activate a zone utility device, such as a warning strobe light or prerecorded visual and/or message the operation of which is responsive to the closure of the zone switch contacts. Also, through programming, the processor may transmit a preprogrammed (audio/visual) page signalling protocol to one or more virtual digital port addresses distributed on an associated data communications bus, As explained above, in connection with the description of an attendant access, lany audio/visual output device addressed either individually or globally by this protocol will respond by generating a prescribed audio/visual message.

Upon completing the servicing of an input type one access request, processor 200 continues to poll the respective inputs of multi-port input driver 173. As long as there is no overriding attendant access request, then whenever an input type one request is asserted active, it will be serviced in the manner described above. Should the controller be occupied servicing a lower priority request at the time of an input type one access, the controller terminates that previous service request and grants immediate access to the input type one access. TELEPHONE INTERFACE (THIRD HIGHEST PRIORITY)

In the present example, the third highest priority of access to the functionality of an attendant paging system served by the control system of the present invention is given to a calling party telephone access. If the controller is servicing either the attendant or a type one priority request, access will be granted to a telephone interface access request, and a busy tone will be returned to the telephone interface. If the attendant access is not active, and if input type one is not active, a select tone will be returned to the telephone interface.

As will be described, a telephone interface access may be any one of four modes or types: Dloop start; 2) ground start; 3) station; and 4) dry loop.

Telephone interface access is by way of a modular jack J4, having respective tip and ring terminals 401 and 402, which are coupled to the tip and ring lines of a telephone line, a ground terminal 403, which is coupled to system ground, and a dry lδop terminal 404, which is coupled to a dry loop detection circuit 405, the output of which DL_DET, at terminal 406, goes active high, in response to a logical low being asserted at terminal 404 by a telephone device (e.g. PBX) . The DL_DET signal is coupled to input port P21 of processor 200.

The tip terminal 401 is coupled via link 411 to a first switchable contact arm 421 of a loop supervision relay 420. The ring terminal 402 is coupled via link 412 through a fuse 409 to a second switchable contact arm 422 of relay 420. Contact arms 421 and 422 are switched from their normally closed positions at terminals 431 and 432 by the energization of a relay winding5 430, which is coupled in circuit between an energizing voltage source terminal 408 and the output of a relay driver 440, the input to which is coupled to a loop enable LO0P_EN terminal 441, the logic state of which is defined by the Ql output port of latching driver 172. As will be described, processor 200 causes a logical low to be asserted at LOOP_EN terminal 441 in response to the logical level at a loop detection LOOP_DET terminal 443, which is coupled to processor input port P15 being asserted active low. (Whenever a L00P_DET signal or a DL_DET signal is asserted an associated light emitting diode, shown at 448, i∑-_5 energized by processor 200 asserting an enabling level to the Q6 output of latching driver 172.)

Terminals 431 and 432 of loop supervision relay 420 are looped through a ring sensing portion 434 of a ring detect opto-

isolator 436, the output of which (RING_DET NOT) is supplied at terminal 438, which is coupled to input port P16 of processor 200. Opto-isolator 436 is operative to provide an active 17-63 Hz ringing signal supplied by an accessing telephone circuit. A second terminal 451 of loop supervision relay 420 is coupled via link 461 to a terminal 473 of a presetable mode switch 470, and to a first end 481 of a first primary winding 483 of coupling transformer 480. A second end 482 of winding 483 is capacitor-coupled to a first end 491 of a second primary winding 493 of transformer 480 and through a resistor 501 to a terminal 513 of presetable switch 470, to a terminal 524 of mode switch 520, which is ganged with mode switch 470, and to one end 531 of a bridge rectifier 530. A second end 492 of a second primary winding 493 is coupled through link 455 to a terminal 563 of mode switch 520 and to terminal 452 of loop supervision relay 420.

Mode switch 420 has terminals 471 and 475 connected together and to line 411; it also has terminals 511 and 512 connected in common to ground. Mode switch 520 has terminals 561, 562 and 566 connected in common to line 412; it also has terminals 521 and 522 connected in common to - 24VDC. Terminal 523 is coupled through resistor 503 to a second end 532 of bridge rectifier 530. Third and fourth ends 533 and 534 of bridge rectifier 530 are coupled to input ports 571 and 572 of a loop detect opto-isolator 570.

Coupling transformer 480 has series-connected secondary windings 601 and 602, a first end 611 of which is coupled via link 621 to hybrid filter circuit 84, and a second end 602 of which is grounded. Link 621 is coupled through voltage divider 603 to line 622. Line 622 is coupled to an output 193 of audio multiplexer 190, and through a precision rectifier circuit 630 to a second input 119 of page/talkback

page/talkback detector 110. The parameters of precision rectifier circuit 630 are chosen to match those of the precision rectifier 111 of AGC circuit 90, in order to enable page/talkback detector 110 to accurately distinguish between page and talkback audio signals.

Like audio signal multiplexers 80 and 100, audio signal multiplexer 190 has a set of control inputs 196, 197 and 198 coupled to receive respective select control signals TONE/PAGE, AA_PHONE AND TB_PHONE, for controlling the coupling of inputs 191 and 192 to output port 193. Input port 191 is coupled over talkback out (TB_0UT) link 631 to the output of an amplitude compression circuit 633 to which talkback amplifier stage 140 is coupled. As described earlier, the speaker of a remote unit to which port 132 is coupled may also serve as a bidirectional audio transducer, sourcing talk-back audio signals from a paging zone speaker.

Links 141 and 142 couple talk-back audio from port 132 to the signal flow path of talk-back amplifier stage 140, so that talkback audio signals from port 132 may be conditioned by stages 140 and 653 and applied through audio signal multiplexer 190 to the telephone interface. The second input port 192 of audio multiplexer 190 is coupled to the tone terminal TONE output 103 of tone signal summing circuit 105, the input to which is coupled to sum respective tone signal inputs (TONE_l, TONE_2) controllably supplied from output ports P36, P37 of processor 200 to tone terminals 701 and 702.

Also coupled in circuit with talk-back amplifier stage 140 are switchable contact arms 721, 722 of a page/talkback relay 720. In their illustrated normally closed positions, switchable contact arms 721, 722 provide respective closed circuit paths for +/-70VAC to attendant speaker amplification circuitry for powering speaker units. In their switched positions,

switchable contact arms 721, 722 provide respective circuit paths from speaker port terminals 731, 732 to talk-back signal amplifier stage 140, so that talk-back audio signals from those zone speakers employed as bidirectional transducers may be amplified and conditioned for application to the telephone interface circuitry.

For this purpose, page/talkback relay 720 has a relay winding 725 which is coupled in circuit between a (+12VDC) voltage terminal 736 and the output of a relay driver 738. The input to relay driver 738 is coupled to terminal 739, to which a page/talk-back relay control input (P/TB-RLY) logic level is controllably asserted by processor 200 from the QI output of latching driver 171. When processor 200 asserts an active high on page/talk-back relay control input (P/TB-RLY) terminal 739, the output of driver 43$ goes low, energizing relay 720 and providing a talk-back path from the paging zone to which speaker port terminals 731 and 732 are connected.

The operation of the telephone interface will now be described for each of the above-identified four telephone interface access modes: DLOOP START; 2) GROUND START; 3)

STATION; and 4) DRY LOOP. For each of these respective telephone interface access modes mode switches 470 and 520 are positioned at a respectively different switch position.

For LOOP START mode, the mode switches 470 and 520 are set at positions shown in Figure 4A. In this first position, the respective sliding contacts of mode switch 470 connect terminal 471 to terminal 473 and connect terminal 511 to terminal 513. Also, the respective sliding contacts of mode switch 520 connect terminal 561 to terminal 563 and connect terminal 521 to terminal 523.

For GROUND START mode, the switches are moved down one position from the positions shown in the drawings. In this

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resistor 503, bridge rectifier 530, opto-isolator 570, transformer winding 493, line 455, sliding contact- connected switch terminals 561-563, line 412 to ring, through the host, return on tip through line 411, sliding contact- connected switch terminals 471-473, line 461 through primary winding 483, resistor 501, sliding contact- connected switch terminals 513-511 to ground.

With current flowing through opto-isolator 570, LOOP_DET terminal 443 is asserted low, which is detected by processor 200. In response to the loop detect signal, processor 200 supplies dial tone via its output terminal ports TONE-1, TONE-2 to input 192 of audio signal multiplexer 190. The TB_TONE control input 197 of mux 190 is asserted high, so as to couple dial tone at input port 192 to output port 193, for application over lines 622-621 through telephone interface coupling transformer 480 to the tip and ring lines of the accessing telephone circuit, via jack J4.

The accessing telephone circuit may then supply DTMF tones for designating a specific zone (or group of zone) , which DTMF tones are coupled over tip and ring, through transformer 480 and applied through hybrid filter circuit $4 to the second input port 82 of audio signal multiplexer 80. Processor 200 will assert the TB_TONE control input of each of the audio signal multiplexers high, incoming DTMF signals are coupled through the PAGE/DTMF circuit path to DTMF decoder 150, where they are decoded and processed as described previously for an attendant access.

In response to paging zone DTMF identification code tones, processor 200 generates a confirmation or warning tone, which is coupled via its tone outputs TONE_l, TONE_2 through summing amplifier 105 to tone terminal 103, which is coupled to the second input 102 of audio signal multiplexer 100. Audio

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accesses the translating zone map in memory and outputs paging signals to the appropriate zone in which the called party (ext 1234) is located. Thus, in an office environment, where plural office personnel are located in a given zone, the extension numbers of their respective desk phones are mapped to the same zone number of their shared zone. The calling party needs only know the extension number of the desk phone to effect a page.

ZONE EXPANSION UNIT (Figures 8 and 8A) Although the embodiment of the invention illustrated in Figures 4A - 7 is configured for eight zones, it should be observed that the invention is not limited to this or any particular number. Where eight bit latches and associated zone switch units (300, shown in Figure 7) are employed, as in the illustrated embodiment, expansion to a larger number of zones is readily accomplished by connecting additional multiple zone switch units (an individual one of which is shown in Figure 8A, to be described below) connected in a daisy- chain configuration by means of one or more zone expansion units coupled to the I ² C bus 200B. As a non-limiting example, a respective zone expansion unit, diagrammatically illustrated in Figure 8B, may be coupled to sixteen zone switches per unit in a daisy-chain interconnect configuration.

With a zone expansion unit add-on, the processor accesses each additional zone using the I ² C bus. To conserve power, each zone expansion switch unit, a respective one of which is shown at 900 in Figure 8A, employs a pair of latching relays 901, 902 in place of the individual relay 307 of the zone switch unit of Figure 7, described above. As a non-limiting example, a respective zone expansion unit shown in Figure 8D may employ a remote eight-bit input/output

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unit 900 is used to provide a closed circuit path connection to an output device whose terminals are coupled to zone terminals 935, 936. This enables the zone expansion switch unit 900 to be effectively employed as an on/off switch for an audio or video device, such as the activating of a prerecorded announcement playback device through one or more paging speakers, or the activation of visual display playback unit to drive a message display device, such as a silent radio, as described above.

When sliding -contacts 952, 953 are moved two positions to the left, so that sliding contact 952 connects terminals 941 and 943, and sliding 953 connects terminals 942 and 944, then, in response to the assertion of one of A ZONEi_RESET, Z0NEi_SET active state to one of input control terminals 911, 912, thereby energizing one of relay windings 901, 902, the zone expansion switch unit 900 is operative to provide +/- 70VADC circuit path connections from contact pair 943, 944 sliding contacts 952, 953, terminals 941, 942, closed switch contacts 931 and 932 and terminals 935, 936, for driving associated speaker amplifiers to zone expansion which terminals 935 and 936 are connected.

When the sliding contacts 952, 953 are moved one position to the left from the position shown in Figure 8A, so that sliding contact 951 connects terminals 941 and 948, and sliding 952 connects terminals 942 and 949, then the zone expansion switch 900 is operative as an input device in accordance with the connection state of terminals 941 and 942. When an external contact closure (e.g. the operation of a push¬ button switch connected across terminals 935 and 936) is operative to bridge zone terminals 935 and 936, a circuit path is established between switch terminals 948 and 949, thereby asserting a low (ground) at the input to driver 951, causing its output Z0NEi_IN at terminal 914 to change state (be asserted active high) . This active high assertion on Z0NEi_IN terminal 914 is read by processor 200 in the course of its periodic polling of the zone inputs of the zone expansion unit via its I ² C bus.

As will be appreciated from the foregoing description, the inability of conventional paging systems to provide either adequate normal paging or emergency information to the variety of individuals including visual messaging" for either standard or emergency page announcements for the hearing-impaired, or audible page announcements for. the visually impaired, is overcome by the paging control system of the present invention, which is configured to be accessible from a plurality of input devices, such as an attendant's position- a telephone interface, telephone night bell, programmable switch devices and digital data communications devices, and is user- programmable to respond to signalling activity sourced from such accessing devices to establish a paging connection to and perform prescribed audio/visual output paging signal functions with respect toone or a plurality of paging zones served by the system. As described above, such output paging signal functions include, but are not limited to, the transmission of audio tone and voice paging signals via an audio signal path from a paging source to one or more (controllably energized) paging loudspeaker amplifiers, the generation of one or more alert tones to a paging zone, talkback audio signalling from the paging zone to a telephone interface, the playback of prerecorded (audio/visual) messages from either or both of audio output (e.g. loudspeaker) and visual output (e.g. silent radio) devices.