Telephone Paging System and Method

This invention generally relates to a telephone paging system and method, and in particular to a system and method for transmitting paging signals based on calls directed to selected telephone extension lines.

It is not uncommon for people to be away from their telephones when they ring. If someone else is not present to pick up the call, an important message might be delayed or missed. And even if someone else does answer the phone, the message may still be delayed or missed if that person does not known the immediate whereabouts to how to contact the intended recipient. A missed, or even delayed, important message can have severe consequences (e.g., if the intended recipient is a doctor).

One solution to this problem has been the development of the paging terminal system which sends signals to a person wearing a remote pager device that informs him that someone is trying to contact him. When a person desires to contact a person subscribing to the paging terminal system (hereinafter "subscriber"), he calls a phone number corresponding to a central paging terminal. The particular phone number called may distinctively correspond to the particular pager worn by the intended subscriber, or the terminal may request the caller to enter a code distinctively corresponding to the subscriber. The paging terminal searches its data base to identify the particular subscriber corresponding to the number called or code number entered, what type of pager he wears, and what signals must be transmitted to activate the pager. A signal which activates the pager of the identified subscriber is then transmitted to all pagers within its range.

Conventional pagers can respond in a variety of ways to the transmitted signal. For example, they can produce a repetitive tone signal (e.g., a "beep") which notifies the subscriber to call an answering service to learn the identity of the caller or hear a recorded message, or they can produce an audio or visual signal containing the message that the subscriber can directly observe.

While this type of system informs a subscriber that someone is trying to contact him, it also has some drawbacks. For example, a caller may typically know the home or work phone numbers of the subscriber, which he may call first. If the subscriber is not present, the caller must known and remember the phone number of the subscriber's paging terminal and, possibly, an additional subscriber identification code. Thus, the caller must go through a number of steps before a paging signal is transmitted to the subscriber. Another drawback is that there is no interactive communication with the system after the subscriber receives the page. If the subscriber wears one of the relatively unsophisticated pagers that only produces a repetitive tone, he must call his answering service to find out the message or the identity of the caller who must then be contacted. Even if the subscriber wears a pager that transmits an audio or visual message, he must still contact the caller to clarify questions or to respond to the message.

The present invention is directed to an improved paging system and method which allows a person subscribing to the system to be paged via the subscriber's existing phone line.

According to this invention, a plurality of extension telephone lines of a conventional telephone line switching means (e.g., a PBX) are selected for connection to the paging system. A detection means detects signals representing calls directed to the selected extension lines. A storing means contains a plurality of different paging code signals, wherein each paging code signal distinctively corresponds to one of the selected extension lines. An identification means identifies the paging codes signal corresponding to the selected extension line for which a call signal has been detected. A transmitting means is provided to transmit the identified paging code signal to a receiving means that is responsive to that particular paging code signal.

In the presently preferred embodiment, the invention interfaces with a switching means that also has the capability to hold a call. A detection means is connected to each selected extension line to sense signals representing rings. When a ring signal is detected on a selected extension line, a control means sends a signal to the switching means to hold the call. The identification means identifies the stored paging code signal corresponding to the selected extension line on which a predetermined number of ring signals has been detected. The transmitting means transmits the identified paging code signal to a plurality of receiving means, one of which is responsive to the transmitted paging code signal.

Thus, in the preferred embodiment, when a predetermined number of ring signals is detected on a selected extension line, a control signal is sent to the switching means to hold the call and a paging code signal corresponding to that extension line is transmitted to a receiving device which is responsive to the paging code signal. This object provides several advantages. For example, a person subscribing to one of the selected extension lines can be directly paged by someone calling his regular telephone number. The caller does not have to remember a special paging terminal telephone number or an identification code for the subscriber. The invention also readily interfaces with a conventional telephone line switching means, thereby facilitating its implementation on an existing phone system and obviating the need for a separate paging terminal system. Further advantages are realized because the call is placed on hold. The switching means used in the preferred embodiment allows a held call to be retrieved from any extension, thereby permitting the intended subscriber to retrieve the call after he is paged. This permits quick interactive communication with the caller.

The invention can also be interfaced with other types of conventional telephone line switching means so that it can take advantage of some of the functions available on these switching means. For example, another embodiment of the invention interfaces with a switching means that permits a subscriber to pick up a call on an extension line from any other extension line. The invention can be interfaced to this switching means to eliminate the control means which places a call on hold. A paging code signal would then be transmitted while allowing the phone to ring. Upon being paged, the subscriber could pick-up the call from any extension line.

Another feature of the preferred embodiment of the present invention is that one of the extension lines of the switching means can be selected for command signals. A ring detection means and a code detection means, which senses signals representing instructions, are connected to the command line. The storing means contains command signals which correspond to a ring signal on the command line or to instruction signals and paging signals which also correspond to instruction signals. The identifying means identifies the command signal corresponding to a ring signal or an instruction signal on the command line and the paging code signal corresponding to a subscriber line or an instruction. The control means sends the identified command signal to the switching means, and the transmitting means transmits identified paging code signals.

By using the command line and appropriate instruction signals, a subscriber can enable or disable his paging code signal or directly page another subscriber.

The invention, together with further objects and advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram of a telephone paging system including a preferred embodiment of the present invention.

FIG. 1a is a circuit diagram of the transmitter level converter of the preferred embodiment of the present invention.

FIG. 1b is a circuit diagram of a voltage regulator used in the preferred embodiment of the present invention.

FIG. 2 is a schematic view of the subscriber line interface of the preferred embodiment of the present invention.

FIG. 3 is a schematic view of the command line interface of the preferred embodiment of the present invention.

FIG. 4 is a schematic view of a subscriber line interface of another embodiment of the present invention.

FIG. 5 is a schematic view of another embodiment of the present invention.

Referring now to the drawings, a preferred embodiment of the improved paging system and method of the present invention will be described in connection with the telephone paging system shown in FIGS. 1-3.

FIG. 1 shows the major components of a telephone paging system 10 which interfaces with a conventional PBX 11. The basic function of the PBX 11 is to provide the capability of switching signals on an incoming telephone line 13 to any one of its extension lines 100-200. Thus, the PBX allows a large number of people subscribing (hereinafter "subscribers") to the various extension lines to be able to receive calls through relatively few incoming trunk lines 13. A typical PBX also permits one subscriber to directly call another subscriber by dialing the latter's extension phone number.

A wide variety of PBXs are available with this switching function (also referred to as a branching or demultiplexing function) as well as with various special functions. A General Dynamics PBX 11 (FCC Reg. No. BJ885Z-6779-PF-E) is connected to the presently preferred embodiment of the invention. This PBX 11 places a call directed to one of the extension lines on hold or "park" when it receives a predetermined command signal on that extension line. The subscriber transmits the appropriate command signal to the PBX 11, for example, by quickly depressing and releasing the hook-lever on his phone and then entering a number from his telephone keypad that represents the call-parking function. The PBX 11 also allows a subscriber to retrieve a parked call from any extension line connected to the PBX 11 by entering an appropriate instruction via the keypad on a push-button telephone.

There are 101 extension lines 100-200 connected to the PBX 11 as shown in FIG. 1. Thirty-one of these extension lines 101-131 are selected for connection to the telephone paging system 10 via the subscriber line interfaces 36. A separate unused extension line 100 is selected for connection to the system via the control line interface 38. Thus, a total of 32 telephone extension lines are selected for connection to the system. The selected extension lines 101-131 which are connected to a subscriber line interface 36 will be referred to as subscriber lines, and the extension line 100 connected to the control line interface 38 will be referred to as the dedicated control line or command line. The persons whose extension telephones are connected to the subscriber lines 101-131 will be referred to as subscribers. The persons trying to direct a telephone call to a subscriber will be referred to as callers.

The basic control of the telephone paging system 10 is provided by the CPU 12, which executes the computer program contained in the program listing appended hereto. The presently preferred embodiment uses a conventional Z-8400 microprocessor for the CPU 12. The CPU 12 as well as the memory 16, SIOs 18, output CTCs 30, event CTCs 32, and PIOs 34 are controlled by timing signals derived from a master clock signal provided by the oscillator 14. The oscillator 14 used in the preferred embodiment is a Vectron CO231T-5, which produces a 19.6608 MHz master clock signal. This crystal frequency is preferred because it can be easily divided to provide the baud rates required by the SIOs 18. It is important that the clock signal provided by the oscillator 14 is stable for the paging formats to work correctly. The oscillator 14 divides the master clock frequency to several different frequencies which are output from different ports of the oscillator.

The memory 16 used in the presently preferred embodiment consists of two 2K.times.8 RAMs (model no. TMS 4016) and up to eight 4K.times.8 EPROMs (model no. 2732). The RAM is used to store variables that may be entered by the user through a conventional video terminal keyboard 19 (see FIG. 5) and program data variables that are used and updated during operation of the system. The EPROM is used to hold the master data base and the operating program for the CPU 12. The operating program is run directly from the EPROM.

The master data base record contains coded signals distinctively corresponding to each subscriber's extension telephone number, pager identification number, status (i.e. whether a subscriber's pager is enabled or disabled), and physical extension line number (e.g.,101-131). The pager identification number is the paging code signal that is transmitted to activate a subscriber's pager. A sample master data base record is included in the program listing appended hereto.

A copy of the master data base record is mapped into the RAM when the system 10 is initialized. These data can then be modified by the user via the video terminal keyboard 19 or some other means. For example, a particular subscriber may initially want his pager to be disabled (i.e., not have paging signals transmitted when his phone rings) when the system 10 is initialized. The subscriber can subsequently directly enable his device by means which will be explained below. In operation the CPU 12 uses the data base stored in RAM, which reflects the current status of the system and each subscriber.

The EPROM is used to store the master data base record and operating program to avoid re-loading that information whenever there is a power interruption. As a further enhancement of the system 10, a conventional non-volatile memory could be used in place of the EPROM and RAM. This would obviate the need for the working copy of the data base presently stored in RAM.

Two conventional SIOs 18 (Zilog model no. Z8440) are used to transmit paging code signals to a transmitter 25 and the video terminal display 19. A conventional General Electric transmitter (part no. 19D43296G1) is used to transmit paging code signals to the subscribers' pagers via a ground plane antenna 26. The antenna 26 is made from wire in a standard ground plane configuration that provides omnidirectional signals corresponding to the paging frequency of the transmitter 25. A Qume QVT102 video terminal 19 is used for monitoring the system, such as displaying system status, and providing a means for adding to or updating the copy of the subscriber data base records stored in RAM.

One of the SIOs provides serial data communication which is compatible with the transmitter 25, and one provides serial data communication which is compatible with the video terminal 19. The transmitter 25 requires a digital signal from the SIO 18 output at a 510 baud rate in accordance with the POCSAG paging format. The video terminal 19 requires a digital signal from the SIO 18 output at a 2400 baud rate in accordance with the ASCII format.

Voltage level converters 20-23 are connected to the output lines of the SIOs 18 to translate output signal voltage levels to voltage levels that are compatible with external peripheral devices (such as the video terminal 19). A conventional Motorola MC1488 or MC1489 level converter may be used for the level converters 20-23. The video terminal 19 is interfaced directly to the level converter 20.

An additional transmitter level converter 24, shown in FIG. 1a, is connected between the level converter 23 and the transmitter 25. The pins 78, 79, 80 of the transmitter level converter 24 are connected to the outputs of the level converter 23 via a conventional 25-pin connector, and the pins 81, 82, 83, 84 85 of the transmitter level converter 24 are connected to the transmitter 25 via a conventional 10-pin connector. The CPU 12 sends a power-up signal to the connector pin 78 via the SIOs 18 in advance of sending the paging code signal data to the connector pin 79. The transistor network 86 converts the voltage level of the power-up signal to the voltage level compatible the transmitter 25 and amplifies the current to the level required by the transmitter. The two potentiometers 87 and 88 adjust the voltage level of the paging code data signal so that it is compatible with the transmitter 25. Connector pins 80, 83, and 84 are tied to a common ground so that the transmitter 25 will have the same ground level as the other components of the telephone paging system 10.

FIG. 1b shows the components of a voltage regulator circuit 89 that provides the bias voltage +V to the transistor network 86, the potentiometer 88, and the transmitter 25 via connector pin 85. The output voltage +V is adjusted via the potentiometer 90 to provide 10 volts. The particular voltage regulator 89 shown in FIG. 1b is designed operate with low power dissipation.

Two conventional control counter-timer circuits (CTC) 30 (Zilog model no. Z8430) are used to provide the clock signals to the clock input ports of the SIOs 18. One CTC 30 provides a clock signal corresponding to the baud rate of signals sent to the video terminal 19, and one provides a clock signal corresponding to the baud rate for signals sent to transmitter 25.

A conventional event CTC 32 (Ziolg model no Z8430) is provided to monitor real-time events. The event CTC 32 counts a predetermined number down to zero, whereupon an interrupt signal is sent to the CPU 12. The interrupt tells the CPU 12 that a predetermined amount of time has elapsed since the last interrupt. The CPU 12 is programmed to perform a predetermined operation in response to the interrupt signal.

In the preferred embodiment, the CPU 12, upon receipt of an interrupt from the event CTC 30, reloads the CTC 30 so it can count down again. The CPU then updates a real-time clock which is stored in software. The CPU 12 then scans each subscriber line interface 36 for detected ring signals. The CPU samples the ring signal on each successive interrupt to measure its duration. If the duration of the measured signal is longer or shorter than the duration of a standard ring signal, the CPU 12 knows the detected signal is not a valid ring signal. The event CTC 32 also may be adapted to schedule additional real-time events that a user may program into the operating program stored in the memory 16.

FIG. 1 also shows seven standard parallel input/output controllers (PIOs) 34 (Zilog model no. Z8420) that connect all the subscriber line interfaces 36 and the command line interface 38 with the CPU 12. The PIOs 34 essentially multiplex the data transmitted between the subscriber line interfaces 36, the command line interface 38, the tone generator 40, the tone decoder 60, and the CPU 12.

FIG. 2 shows the details of a subscriber line interface 36 for the subscriber line 101. The subscriber line interfaces for the other subscriber lines 102-131 are identical in structure and function. In the preferred embodiment, two subscriber line interfaces 36 are mounted on a conventional printed circuit card (e.g., BBL part no. PC908).

The existing subscriber extension line 101 actually consists of two lines 42 and 43. A standard optical isolater ring detector 45 (General Electric model no. H11AA1) is connected across lines 42 and 43. When the ring detector 45 senses a signal on lines 42 and 43 representing a telephone ring, the output line 50 from the ring detector to the PIO 34 goes into a low state. A 2.2 microfarad capacitor 46 is connected in series with an 8.2K ohm resistor 47 on the input side of the ring detector 45. The capacitor and resistor values are chosen to only permit ring signals on lines 42 and 43 pass to the ring detector 45. A standard ring signal will produce a 90 volt AC signal across lines 42 and 43 for a standard duration of time. The ring detector 45 has an internal optical isolation feature so that its output and the connected circuitry of the system 10 will be electrically isolated from the PBX 11. Thus, the telephone paging system 10 is transparent to the PBX 11. A conventional voltage source 49 is connected in series with a biasing resistor 48 to provide the voltage for the ring detector 45.

The subscriber line interface card 36 shown in FIG. 2 also includes a relay driver 53 which converts a 0-5 volt data signal on the input line 51 to a 0-12 volt signal. One control register 52 provides the signals on lines 51 and 51' for two subscriber line interfaces 36. In the presently preferred embodiment, two subscriber line interfaces 36 and one control register 52 are mounted on one printed circuit card (e.g., BBL model no. PC908). Accordingly, there are a total of 16 control registers 52 for the thirty-one subscriber line interfaces 36 and the one control line interface 38 in the system 10. (The control line interface 38 is on the same card as the first subscriber line interface 36.)

The inputs to the control register 52 include the command CLOCK line 68 and the command DATA line 67 which are also connected in parallel from the PIOs 34 to every other control register 52 provided on the subscriber line interfaces 36. Each control register 52 has its own command ENABLE line 66 which is connected to the PIOs 34. The CPU 12 clocks command data serially to every control register 52 via the CLOCK and DATA lines. The command data signals include signals which activate a relay driver 53 and signals which do not activate a relay driver. The control register 52 internally stores the activate and non-activate data signals in parallel so that the activate signals correspond to the relay driver 53 connected to the subscriber line 101 on which a ring signal has been detected. The CPU 12 sends a command signal on the ENABLE line 66 to the control register 52 which is connected to the subscriber line interface 36 which detected a ring signal. The activate signals are then sent on line 51 to the relay driver 53, and the non-activate signals are sent to the other relay driver of the subscriber line interfaces on the same card.

The signal output from the relay driver 53 energizes the relay 53, thereby closing the switch 55. When the switch 55 is closed, signals from a tone generator 40 can be transmitted to the PBX 11 via the input lines 57 and 58, the transformer 56, and the subscriber extension lines 42 and 43. The presently preferred embodiment uses a conventional relay driver (e.g., the Motorola MC1413 or the Sprague ULN2002), a conventional relay (model no. AZ7-4D-12DE), and a conventional transformer (model no. T1449).

The relay 54 is set to keep the switch 55 in a normally open position. In this state, ring signals on lines 42 and 43 are transmitted to the extension phone which then rings. However, when the ring detector 45 detects a ring signal on lines 42 and 43, the CPU 12 sends a command signal through the PIOs 34 and control register 52, to the relay driver 53 in the manner described above. The relay 54 closes the switch 55, thereby putting the transformer 56 across the subscriber lines 42 and 43. This command signal on input line 51 is a pulse signal which keeps the switch 55 closed long enough so that the PBX 11 thinks that the extension phone on lines 42 and 43 has been answered. The CPU 12 then sends a second command (or control signal) to the relay driver 53 that "flashes" the relay 54. That is, the relay 54 opens and closes again quickly, which signals the PBX 11 to prepare for a PBX control signal. Without the telephone paging system 10, a flash may typically be generated by pressing the hook receiver down on a conventional extension phone and quickly releasing it.

After the relay 54 has flashed, the tone generator 40, under control of the CPU 12, sends a DTMF tone signal to the PBX 11 which represents a particular PBX command (e.g., to part the call). The tone generator 40 includes a standard DTMF encoder (Mostek model no. MK 5087) and a standard tone generator (Signetics model no. NE567) mounted on a printed circuit card found in many conventional paging terminal systems (e.g., BBL Part no. PC9110). The DTMF encoder generates sixteen standard dual-tone, multi-frequency (DTMF) tones which correspond to the keys on a push-button telephone keypad. One of these DTMF tones is output by the tone generator 40 in response to a four-bit command signal from the CPU 12. The tone generator is used to generate "beep" tones and a "ring" tones for a caller to hear. The "ring" tones are constantly fed directly from the tone generator 40 to the PBX "music on hold" port via line 64. Thus, the caller hears "ring" tones whenever his call is parked, even while the system 10 sends paging code signals to the subscriber. The "beep" tones are constantly fed to the control line interface 38. The CPU 12 sends command signals to the control register 52a on the control line interface 38 which selects the "beep" tones via line 59.

FIG. 3 shows the basic components of the control line interface 38, which are identical of the components of a subscriber line interface 36, except that a tone decoder 60 is also bridged across the command line 100. The components of the command line interface 38 which are identical in structure and function to those components comprising the subscriber line interface 36 are given the same reference number as the corresponding component in FIG. 2 plus the suffix "a". A conventional DTMF tone decoder card 60 (e.g. BBL part no. PC908-2), which contains Mitel MT8865 and MT8860 chips, is used to sense DTMF tones generated by depressing keys on the telephone keypad that represent instructions to the system 10. The first Mitel chip separates the high frequency and low frequency components of the sensed DTMF tone signal. The second chip determines the particular telephone key corresponding to the sensed tone by determining the particular frequency of the high and low tone components. The digits or symbols (i.e., "#" or "*") representing the decoded instruction signals are stored in an internal buffer of the tone decoder on a first-in-first-out (FIFO) basis. The CPU 12 sends a strobe signal to the tone decoder 60 via the PIOs 34 and the input line 62 to place the first digit in the tone decoder buffer on the output line 61 and to position the next digit stored in the buffer. The CPU 12 sends this strobe signal until all the digits stored in the tone decoder buffer have been placed on output line 61. The decoded tone signals put on output line 61 are five bits lone. Four bits represent the digit or symbol corresponding to DTMF tone, and one digit represents whether or not the data is valid. These data bits are sent to the CPU 12 via the PIO 34. The operating program contains the command signals that correspond to the instructions represented by the decoded tone signals.

The elements described in FIGS. 1-3 comprise the basic hardware of the presently preferred embodiment of the invention. Most of these elements are comprised of standard off-the-shelf components. Moreover, many of these components can be found on printed circuit cards used in conventional paging terminal systems. For example, one control CTC 30, one SIO 18, and two level converts 20, 21 can be found on BBL part no. PC984; the CPU 12 and the memory 16 can be found on BBL part no. PC9700; the event CTC 32 can be found on BBL part no. PC985; and two of the PIOs 18 can be found on BBL part no. PC982.

The CPU 12, which provides the basic control for all components of the system, operates in accordance with the software program stored in the EPROM of memory 16. A program listing of the presently preferred software program that is stored in the EPROM is submitted herewith as an appendix. The appended listing is written in Z-80 assembler language. One skilled in the art would be able to readily adapt this program to the hardware previously described to make and use the present invention. Thus, the six sections of the appended program will only be described generally. A more detailed description of the program can be discerned from the program listing and its comment statements.

The first section is the Supervisor section which initializes the PIOs 34, the event CTC 32, the control CTCs 30 and the SIOs 18. The Supervisor section also maps a copy of the master data base record from the EPROM into the RAM for storage of temporary data variables.

Since these components can be programmed to operate in several different modes, the Supervision section initializes them in accordance with the Table 1 below. The initialization of the ports of the PIOs 34 will be self-explanatory to one skilled in the art.

The first channel of the event CTC 32 is set up in timer mode to count down to zero. The second channel of the event CTC 32 is set up in counter mode to count the number of times the first channel counts down to zero. The output of the first channel is connected to the input of the second channel of the event CTC 32 so that each time the first channel reaches zero it decrements the counter of the second channel. When the counter of the second channel reaches zero, it sends an interrupt to the CPU 12 which possesses it in the manner described above. The first channel is reset by the CPU 12 whenever the CPU receives an interrupt from the second channel. The first channel then immediately begins to count down again.

The two control CTCs 30 each use only one channel on each CTC chip. One control CTC 30 is set up to provide a clock signal to the video terminal SIO 18 everytime the CTC counts down to zero. This clock signal is 16 times the 2400 baud rate required by the video terminal 19. The other CTC is set up to provide a clock signal to the transmitter SIO 18 everytime this CTC counts down to zero. This clock signal is equal to 510 baud rate required by the transmitter 25. Once the two control CTCs 30 are set up in this manner they will continuously count down to zero and provide the clock pulse to the SIOs 18. These CTCs do not generate any external interrupts to the CPU 12.

The SIO 18 connected to the video terminal 19 is set up to divide the clock signals it receives from the video terminal control CTC by sixteen. This SIO then outputs 8-bit asynchronous signals to the video terminal 19 at a 2400 baud rate. These signals include a start bit, 7 data bits, a parity bit, and a stop bit. If the video terminal SIO detects a variation in the stop bit or parity, it sends an interrupt to the CPU 12 indicating there is a data transmission error. The video terminal SIO also sends the CPU 12 interrupts whenever it receives a byte of data input from the video terminal 19. The CPU 12 then reads this data and stores it in the memory 16. The transmitter SIO 18 outputs data to the transmitter 25 at the 510 baud rate input by the transmitter control CTC. The data is output as synchronous signals. The number of bits in each data character varies in accordance with the POCSAG format. Both SIOs 18 send interrupts to the CPU 12 when they output a character, thereby emptying their internal transmitter buffers. In response to this interrupt, the CPU 12 sends another byte of data to the empty transmitter buffers. Once the SIOs 18 are initialized, they are ready to receive data and operate in the manner described. The SIOs 18 do not respond to transitions on external devices.

The second second controls the detection of ring signals on the subscriber lines 101-131 and the command line 100, the detection of instruction signals on the command line 100, the identification of paging code signals distinctively corresponding to the subscriber lines on which ring signals have been detected or to instructions detected on the command line and the identification of command signals corresponding to ring signals or instruction signals detected on the command line, and the transmission of identified command signals to the tone generator 40, the tone decoder 60, the subscriber line interfaces 36 and the control interface 38.

The third section controls the output format of the identified paging code signals which are stored in the memory 16 in BCD format. Each paging code signal can be up to 7 digits. This section converts the BCD format paging code into a 4 byte binary pattern in accordance with the POCSAG paging format. POCSAG is a format for processing paging signals which is well known in the pertinent art. All the paging code signals which have been identified are converted to the POCSAG format in the memory 16 in batch. These POCSAG format paging code signals are then serially transmitted to the SIO 18 connected to the transmitter 25 one byte (8 bits) at a time in the manner described above until all bytes of data in the batch have been sent to the transmitter SIO 18. Prior to sending the first byte, however, a wake-up signal is sent to this SIO 18, which is transmitted to the pagers telling them to listen for their particular POCSAG format paging code signal. The bytes of data sent to the transmitter SIO 18 representing the paging code signals are synchronous signals which are frequency shifted in a conventional manner.

A fourth section is the Video Terminal Driver section which controls the output of data to SIO 18 connected to the video terminal 19. This section takes a copy of the identified paging code signal, which is in stored in memory 16 in BCD format, and converts it to the ASCII format. The extension number of the subscriber line corresponding to this paging code signal and the current value of the real-time clock are also identified and converted to ASCII format. These signals are then sent to the video terminal SIO 18 in the manner described above. These signals are then sent from this SIO to the video terminal 19 at 2400 baud.

The fifth section of the software controls the input of the data base record into the memory 16 via the video terminal 19. This section also controls editing of the copy of the master data base record in the RAM via the video terminal 19. This data is input to the memory via the video terminal SIO 18 in the manner described above.

The last section of the software defines the layout of the RAM of memory 16 for storing the copy of the data base record which is mapped in from the EPROM and the data for temporary and program variables.

The telephone paging system 10 embodying the present invention is intended to transmit paging code signals to a remote pager worn by a subscriber. Any type of conventional pager that produces a paging signal in response to a distinctive paging code signal in the POCSAG format can be used. Each subscriber wears a pager that is responsive only to the paging code signal distinctively corresponding to his assigned extension line. The pager may output any type of well known paging signals in response to the paging code signal.

Having described the various elements that comprise the telephone paging system of the presently preferred embodiment of the invention, its operation will now be described. As a preliminary step, the extension phone number, pager code identification number, initial status, and physical extension line number for each subscriber are programmed into the EPROM. When the system is activated, the data base record stored in the EPROM is mapped into the RAM, and the RAM is set up for the storage of temporary and program variables. The CPU 12 then initializes the SIOs 18, the control CTCs 30, the event CTC 32, and the PIOs 34 in the manner described above.

The paging operation of the preferred embodiment is initiated in response to the first ring signal detected on a selected subscriber line 101-131. When the PBX 11 sends a ring signal to a subscriber's extension phone, (e.g., subscriber line 101), the ring detector 45 will force output line 50 into a low state. The CPU 12 will cooperate with the event CTC 32 to determine if output line 50 remains in the low state long enough to correspond to a ring signal on the subscriber extension line 101. If so, the CPU 12 sends an enable signal to the control register 52, thereby putting a command signal on input line 51. The command signal is amplified by the relay driver 53 to energize the relay 54 which closes the switch 55. The transformer 56 is then bridged across lines 42 and 43 of the subscriber line 101.

The switch 55 is closed for an amount time that indicates to the PBX 11 that the phone on subscriber line 101 has been answered. The PBX 11 will then stop producing ring signals on subscriber line 100. Nevertheless, the caller still hears ring signals that the tone generator 40 sends to the music on hold port of the PBX 11 via line 64 while his call is parked.

The CPU 12 then sends a second command signal to input line 51 via the PIOs 34 and the control register 52, which causes the relay 54 to flash the switch 55. This flash signals the PBX 11 to prepare to receive a PBX command signal. The CPU 12 then signals the tone generator 40 to send a DTMF signal to lines 42 and 43 of the subscriber line 101 via input lines 57 and 58 and transformer 56, which will command the PBX 11 to park the call on subscriber line 101.

Next the CPU 12 sends a command signal the relay driver 53 via the PIOs 34 and the control register 52, that de-energizes the relay 54, thereby opening the switch 55. The system 10 is then disconnected (or released) from the subscriber line 101. The PBX 11 interprets the open switch 55 to mean that the subscriber on extension line 101 has hung up his phone.

While the PBX 11 holds the call on park, the CPU 12 searches the memory 16 to identify the pager identification number (paging code signal) corresponding to the physical subscriber extension line 101 on which the ring signal was sensed. The CPU, under control of the output format section of the software, sends a key-up signal to the transmitter 25 via the SIOs 18 and connector pin 78 of the transmitter level converter 24. Dummy data is then sent to the transmitter 25 via connector pin 79 for about 1 second while the transmitter warms up. After this is completed, a wake-up signal is sent to the transmitter 25 via connector pin 79 to alert all pagers to prepare for a paging code signal. The CPU 12 then converts the identified paging code signal to the POCSAG format, converts a copy of the identified paging code signal, the corresponding subscriber line and the current real-time clock value to the ASCII format, and sends them to the SIOs 18. The SIOs 18 will serially transmit the POCSAG-format paging code signal to the transmitter 25 via connector pin 79 and the ASCII-format signals to video terminal 19 in batch in accordance with their respective baud rates as controlled by the control CTCs 30. The transmitter level converter 24 will translate the voltage level of paging code data signals input at pin 79 to a level compatible with the transmitter 25. After the last byte of the POCSAG-format paging code signal has been transmitted to the SIOs 18, the CPU 12 sends more dummy data bytes to the transmitter 25 via the SIOs 18 to assure that all bytes of the paging code signal were transmitted. The key-up signal is then terminated and the paging process can begin anew.

The transmitter 25 transmits the paging code signal via the antenna 26 to all pagers within the range of the transmitter 25 and antenna 26. The pager worn by a subscriber which is responsive to the particular POCSAG format paging code signal transmitted will produce a paging signal. The subscriber will then know that someone has directed a call to his extension line and that the call is parked. The subscriber can retrieve the parked call from any other extension phone on the PBX 11 by entering the appropriate PBX command via the telephone keypad.

A subscriber may enable or disable his pager via the command line 100 by entering the appropriate instructions via any extension telephone keypad. The subscriber first dials the extension telephone number corresponding to the command line 100. The ring detector 45a responds by putting line 50a in a low state for a period of time corresponding to a ring signal. The CPU 12 then sends a command signal to the relay driver 53a via the control register 52a and PIOs 34. The relay 54a closes the switch 55a and keeps it closed until the caller hangs up on the phone. In the meantime, the CPU 12 sends a command signal to the tone generator 40 to send a DTMF tone corresponding to a "beep" to lines 57a and 58a of the control line interface 38. This "beep" is routed to the subscriber by the PBX 11 by connecting the caller's extension to the command line 100. Upon hearing the "beep", the subscriber-caller enters his own extension phone number from the telephone keypad, which represents a first instruction signal. The tone decoder 60 decodes the DTMF tones that represent the digits of the phone number entered. The CPU 12 strobes the port of the tone decoder 60 with a strobe signal until it receives the data representing all digits on the data bus 61. The CPU 12 then sends another command signal to the tone generator 40 to produce two "beep" signals. Upon hearing the two "beep" signals, the subscriber depresses either the "*" or a "#" telephone key, which are enable or disable instruction signals, respectively. The tone decoder 60 decodes the DTMF tones that represent these two keys, and the CPU 12 sends a strobe signal over line 62 to put this data on line 61. The CPU 12 then searches the memory 16 to identify the subscriber corresponding to the extension number entered and updates the operating status of his paging code signal according to the second instruction signal entered. The updated status is stored in the RAM of memory 16.

The CPU 12 next sends the first command signal to the tone generator 40 to produce the "beep" tone signal again. Upon hearing this signal, the subscriber-caller may enable or disable the paging code signal of another subscriber by following the procedure just described. If, however, he pauses too long before entering the next instruction signal, the CPU 12 will command the tone generator 40 to produce an alternating "beep-beep" signal, thereby indicating the completion of this function. The subscriber-caller then must dial the command line 100 again to enable or disable another subscriber.

When this enable/disable function is available, the telephone paging system described above operates slightly differently. After a ring signal is detected on a subscriber line, the CPU 12 first identifies the status of that subscriber line before it seizes the subscriber line to answer the call. If the line is enabled, the telephone paging system proceeds to park the call and transmit a paging code signal to the subscriber in the manner described above. If the paging code signal for that subscriber line is disabled, however, the system never closes the relay 54. Thus, the phone is allowed to ring and no paging code signal is transmitted.

A subscriber can also directly page another subscriber via the command line 100. The subscriber-caller first dials the extension phone number corresponding to the command line 100 from any phone connected to the PBX 11. The CPU 12 answers the line and sends the first "beep" tone in the same manner just described for the enable/disable function. Upon hearing the "beep", the subscriber-caller enters from his telephone keypad the extension phone number of the subscriber he wishes to page (the "subscriber-pagee"), which represents a first instruction signal. The tone decoder 60 decodes the DTMF tones representing the digits of the number entered, and the CPU 12 sends a strobe signal to put this data of line 61. The CPU 12 then sends the second command signal to the tone generator 40 to produce two "beep" tones. Upon hearing the two "beeps", the subscriber-caller enters from his keypad the numbers 1, 2, 3 or 4, which represent four distinctive POCSAG paging tone patterns. This instruction signal is decoded by the tone decoder 60 and sent to the CPU 12 over line 61. The CPU 12 then searches the memory 16 to identify the subscriber-pagee corresponding to the extension phone number entered. The CPU 12 also identifies one of four POCSAG paging patterns corresponding to the second instruction entered. The CPU 12 converts the identified paging code signal into the POCSAG paging format that includes the paging format specified. This paging code signal is sent to the transmitter 25 via the SIOs 18 in the manner described above. The CPU 12 then sends a third command signal to the tone generator 40 to produce the alternating "beep"-"beep" tone for the subscriber-caller to hear, which represents that the operation has been completed. The subscriber-caller then hangs up his phone.

A subscriber may also test his pager by directly paging himself in accordance with the procedure described above. Upon hearing the first beep tone, the subscriber would enter his own extension telephone number. The system 10 would then send a paging code signal that would activate the subscriber's own pager.

FIG. 4 shows the subscriber interface card 36a which may be used in another embodiment of the invention. This type of subscriber interface card would be connected to a subscriber extension line 101b on a PBX 11 that has a direct-call-pickup function. This allows a subscriber to pick up a call on an extension line from any other extension line. A PBX with this directed call pick-up function can also forward a call to another extension line after a predetermined number of rings when requested by a subscriber. These functions are executed by the PBX 11 independent of the telephone paging system 10.

The modified subscriber interface card 36a, as shown in FIG. 4, includes a ring detector 45b connected across lines 42b and 43b of the subscriber extension telephone line 101b. A capacitor 46b and resistor 47b are connected in series to one of the input ports of the ring detector 45b. The ring detector 45b is optically isolated from the PBX 11 and powered by a voltage source 49b and biasing resistor 48b. These components cooperate to detect a ring signal on subscriber line 101b, and in response thereto place output line 50b in a low state in the same manner described above for the corresponding components in FIG. 2. The CPU 12 cooperates with the other components shown in FIG. 1 in the same way described above to transmit a paging code signal distinctly corresponding to the subscriber assigned to extension line 101b.

An important advantage of the subscriber line interface 36 or 36a is that it does not require a relay driver, relay, switch, transformer, control register, or equivalents thereof, to answer the call and then put it on park. In this embodiment, the subscriber line interface 36a and the other components of the telephone paging system 10 shown in FIG. 1 cooperate to transmit a paging code signal upon detection of the first ring signal on the subscriber line 101b while only monitoring ring signals on the subscriber line 101b. Thus, the phone on the subscriber line 101b continues to ring while the telephone paging system transmits a paging code signal corresponding to subscriber line 101. This also allows the PBX functions to operate concurrently with the system 10 (for example, transferring the call to another extension line after a predetermined number of ring signals, if requested by the user).

As shown in FIG. 1, the presently preferred embodiment of the invention does not select all the available extension lines 132-200 for connection to the telephone paging system 10. Another embodiment of the present invention is shown in FIG. 5 which allows the additional subscriber extension phone lines to be interfaced to the telephone paging system 10 via the remote line interface units 70, 71, 72. In this embodiment the dedicated control line 100 and the subscriber extension lines 101-131 are connected to the PBX 11 and the components of the telephone paging system 10 as explained above in connection with FIGS. 1-3.

The remote line interface card 70 would be connected across one of the extension lines 132-200. The remote line interface card 70 could be configured much like FIGS. 1 and 2 or 4, except that only one SIO chip 18 and one control CTC chip 30 would be required. The remote line interface card would detect ring signals on the selected remote extension line and send signals down the serial data lines 74, 75, 76 to the telephone paging system 10. The signal transmitted down the serial data line would represent that the particular remote extension line (e.g. 132) was ringing. Since this data is being transmitted serially, the beginning and end of this data would have to be marked. Only two SIO ports would be necessary: one to receive input from the remote line interface unit above and one to output the data to the remote line interface unit or the telephone paging system 10 below. The oscillator used on the remote line interface unit would not have to be as stable as the oscillator 14. The data base record stored in the memory in the telephone paging system 10 would also contain coded signals corresponding to the extension telephone number, pager identification number, status, and physical extension line number of each remote line connected to the system 10.

Using the remote line interface units 70, 71, 72, additional subscribers can be added to the telephone paging system 10 at minimal expense. The remote units will monitor each subscriber phone line and signal any "ringing" lines back to the system unit 10. The system 10 reads the digital information arriving from the serial communication line 76 and decodes the information to determine which remote phone line was ringing. The telephone paging system 10 could then proceed to page the subscriber to the remote line in the same manner described above for one of the subscribers line interfaces 36.

The preferred embodiment described above is a telephone paging system interfaced to a conventional telephone line branching system which has the capability of parking a call and conventional pagers that are responsive to POCSAG format paging code signals. However, it should be apparent that the present invention can be interfaced with other types of telephone line branching means or pagers. For example, the present invention could be adapted for use with a PBX that has voice synthesized announcements that could be played to the caller to indicate that the subscriber called is being paged. The present invention could also be used with a higher powered transmitter that would extend the range of the transmitted paging code signals from building wide to city-wide. At this point, a "meet-me" function in the PBX could be used by the subscriber receiving the call to accept the call at any phone in the city.

Other embodiments of the present invention should be also apparent to those skilled in the art from the foregoing description. For example, multiple transmitters 25 could be implemented in the system 10 so that more than one subscriber can be paged simultaneously. Also, a paging system other than POCSAG could be used. The system could also be modified to require the detection of more than one ring signal on a subscriber's extension line before transmitting a paging code signal. A PBX-type branching means may also be developed that identifies the intended subscriber line of an incoming call and then transmits a paging code signal in accordance with the present invention without putting a signal on the intended subscriber line.

Of course, it should be understood that various other changes and modifications to the preferred embodiment described above will be apparent to those skilled in the art. It is intended that the foregoing description be regarded as illustrative rather than limiting and that it be understood that it is the following claims, including all equivalents, which are intended to define the scope of the invention.