Paging universal remote control system

What is claimed is:

1. A method for communicating binary information signals and analog information signals in a paging system having at least one paging terminal, a paging system encoder, a paging system decoder, a paging system transmitter and a means for coupling said paging system encoder to said paging system decoder, wherein said paging system encoder, at separate times, generates either analog or binary signalling formats in response to analog or binary requests from said paging terminal, and further wherein said paging system decoder being coupled to said paging transmitter controls the transmission format of said paging transmitter, said method including the steps of:

(a) in response to an analog or binary paging request from said paging terminal, transmitting first and second control tones from said paging system encoder to said paging system decoder for a first predetermined period of time;

(b) in response to an analog paging request input, enabling an audio signal path from said paging system encoder to said paging system decoder, and transmitting an analog information signal followed by a pause and then, in response to a binary paging request input, enabling a binary signal path from said paging system encoder to said paging system decoder and transmitting a binary information signal;

(c) in the absence of said analog paging request input and in response to a binary paging request input, generating a pause for a second predetermined period following said second control tone, and transmitting from said paging system encoder to said paging system decoder, a binary information signal;

(d) sequentially detecting the first and second control tones, with said paging system decoder, and thereupon providing a path from said paging system decoder to said paging transmitter for the transmission of analog information signals from said paging system decoder to the paging transmitter;

(e) searching for a binary information signal with said paging system decoder, if the analog information signal is not received within a second predetermined period of time;

(f) interrupting said analog signal path, and enabling a binary signal path in response to detecting a binary information signal after said second predetermined period of time; and

(g) repeatedly searching for one of said control tones and, in response to detecting same, enabling either said analog signal path or said binary signal path without dekeying the transmitter.

2. A paging remote control system for transmitting analog and binary paging information, comprising:

(a) paging terminal means for inputting paging information and generating an analog or a binary paging information signal;

(b) paging encoder means coupled to said paging terminal means for selectively combining said analog and binary information signals into a predetermined encoded format to generate a composite output signal; wherein said predetermined encoded format includes a first control tone to indicate the transmission of analog information and a pause to indicate the transmission of binary information;

(c) linking means coupled to said paging encoder means for transferring said composite output signal;

(d) paging transmitter means for transmitting said analog or binary paging information signal wherein said paging transmitter means includes means for switching between analog and binary paging modes without dekeying said paging transmitter;

(e) decoder means being coupled to said linking means for receiving said composite signal, and further coupled to said paging transmitter means, said decoder means switching said paging transmitter between analog and binary signalling modes as indicated by said predetermined encoded format of said composite signal for recovering said analog and binary paging information signals from said composite output signal and selectively coupling said analog and binary paging information signals to said paging transmitter means.

3. The paging remote control system of claim 2, wherein said paging encoder inhibits generating analog paging information while binary paging information is being generated.

4. A paging remote control system for transmitting analog and binary paging information, comprising:

(a) first paging terminal means for inputting analog paging information and generating an analog paging information signal;

(b) second paging terminal means for inputting binary paging information and generating a binary paging information signal;

(c) paging encoder means coupled to said first and second paging terminal means for selectively combining said generated analog and binary paging information signals in accordance with a predetermined encoded format to generate a composite output signal, wherein the predetermined encoded format includes at the beginning a first activation signal and a function signal;

(d) linking means coupled to said paging encoder means for transferring said composite output signal;

(e) paging transmitter means for transmitting said analog or binary paging information signal wherein said paging transmitter means includes means for switching between analog and binary paging modes without dekeying said transmitter;

(f) decoder means coupled to said linking means, and further coupled to said transmitter means, said decoder activating said transmitter means in response to receiving the first activation signal and the function signal, said decoder further switching said paging transmitter between analog and binary signalling modes as indicated by said predetermined encoded format and recovering said analaog and binary paging information signals from said composite output signal and selectively coupling said analog and binary information signals to said paging transmitter means.

5. A method for transmitting paging information to a plurality of paging receivers via a plurality of remote paging transmitter stations in a paging system, the paging system having at least one paging terminal coupled to a paging system encoder, each remote paging transmitter station having a paging transmitter coupled to a paging decoder, each of the paging decoders being response to a communications link coupled to the paging system encoder, said method including the steps of:

(a) generating a the paging terminal, at separate times, a paging information signal and a paging mode control signal, the paging information signal representative of paging information and the paging mode control signal representative of the mode of the paging information;

(b) transmitting the paging information signal and paging mode control signal to the system encoder;

(c) coding at the paging system encoder the paging information signal into a coded signal having a predetermined encoded format in response to the paging mode control signal, wherein the predetermined encoded format includes at the beginning a first activation signal and a function signal;

(d) transmitting the coded signal through the communication link to at least one of the plurality of remote paging transmitter stations;

(e) receiving the coded signal at the remote paging transmitter station;

(f) decoding at the paging decoder the coded signal for recovering the paging information signal and the paging information mode signal, the paging decoder generating a paging transmitter control signal in response to receiving the first activation signal and the function signal;

(g) activating, in response to the paging transmitter control signal, the paging transmitter to receive from the paging decoder the paging information signal;

(h) transmitting by means of the paging transmitter the paging information signal to a plurality of paging receivers; and

(i) maintaining the activation of the paging transmitter until the paging decoder detects a predetermined period of cessation of transmitted coded signal.

6. The method of claim 5, wherein step (a) of generating further includes the step of generating an analog paging information signal and an analog mode control signal in response to an analog paging request.

7. The method of claim 6 wherein step (c) of coding further includes the step of coding in response to the analog mode control signal, the analog paging information signal into an analog data format wherein the analog data format comprises the function signal immediately followed by the analog paging information signal.

8. The method of claim 7, wherein step (c) of coding further includes the steps of:

(j) repeating for a plurality of analog paging requests the corresponding paging information signals into the analog data format until an absence of an analog paging segment; and

(k) generating a first predetermined period of silence following the last analog paging information signal.

9. The method of claim 7, wherein step (c) of coding further includes the steps of:

(l) waiting at the paging encoder for a subsequent paging information signal and paging mode control signal;

(m) determining at the paging encoder whether the paging mode control signal is a binary mode control signal or an analog mode control signal;

(n) immediately transmitting the analog paging information signal if the paging mode control signal is an analog mode control signal;

(o) transmitting a second predetermined period of silence followed by the binary paging information signal if the paging mode control signal is a binary mode control signal.

10. The method of claim 5 wherein step (a) of generating further includes the step of generating a binary paging information signal and a binary mode control signal in response to a binary paging request.

11. The method of claim 10, wherein the step (c) of coding further includes the step of coding in response to a binary mode control signal, the binary paging information signal into a binary data format, wherein the binary data format comprises a second predetermined period of silence followed by a binary control word and binary data.

12. The method of claim 10, wherein step (c) of coding further includes the steps of:

(p) repeating for a plurality of binary paging requests the corresponding binary paging information signals into the binary data format until an absence of a binary paging request; and

(q) generating a third predetermined period of silence following the last binary paging information signal.

13. The method of claim 10, wherein step (c) of coding further includes the steps of:

(r) waiting at the paging encoder for a subsequent paging information signal and a paging mode control signal;

(s) determining whether the paging mode control signal is a binary code control signal or an analog mode control signal;

(t) immediately transmitting the binary paging information signal if the paging mode control signal is binary; and

(u) transmitting a fourth predetermined period of silence followed by the activation signal and the analog paging information signal if the paging mode control signal is an analog mode control signal.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

This invention relates to the field of the paging base station and terminal communications using both binary signalling and analog signalling, and more particularly to the signalling scheme and apparatus for implementing a base station and terminal communications link for interactively transmitting both binary and analog signals.

In the past a paging base station was required to dekey its transmitter when changing for transmission of an analog signal to transmission of a binary signal or vice versa. To initiate an analog page, conventional paging systems utilize a sequence of a high level guard tone signal, a functional tone signal and a tone or voice signal accompanied by a low lever guard tone signal. To enter a binary paging mode, a prior art remote control paging encoder removes all activity from the remote control link for at least 300 ms causing the transmitter to dekey. The transmitter then rekeys in the binary mode after the remote site received a burst of FSK paging signals from the paging system encoder, equivalent to a binary comma for 100 ms.

A prior art paging system of this type is described in Motorola document number 68P06905B33 (1980) entitled "MICOR Tone and Binary Paging Transmitter Station." This instruction manual is available from the Service Publication Department of Motorola, Inc., 1301 East Algonquin Road, Schaumburg, Ill., or from Motorola C & E Parts, 1313 East Algonquin Road, Schaumburg, Ill.

This is disadvantageous in certain respects. By requiring dekeying of the transmitter, a signal such as a binary page followed by a voice message must be dekeyed after the binary signal and then rekeyed for the analog voice portion of the transmission and then dekeyed again and rekeyed for a binary end of transmission message. The result of this was a noise burst at the end of the voice message and prior to the binary turn-off code for the pager. The noise burst resulted from the loss of carrier from dekeying the transmitter.

It is well known that different modulation techniques are necessary for the appropriate transmission of binary and analog signals. Therefore, it is desirable to have a technique whereby both analog and binary signals can be sent to a pager by way of different modulation schemes without first dekeying the paging base station. Moreover binary pagers with voice messages require the base station to quickly transfer from an analog modulation mode to a binary modulation mode. Therefore, it is important to provide a signalling scheme whereby the base station can perform such a transition with a minimum of effort and without introducing extraneous signals that might be picked up by the binary pager. Also, dekey/rekey reduces system thru-put which is undesirable on heavily loaded channels.

SUMMARY OF THE INVENTION

Briefly described, the present invention contemplates a paging remote control system which comprises a series of predetermined tones and timed pauses. In accordance with the signalling scheme of the present invention a paging transmitter keys in an analog or binary modulation mode or makes transitions from one modulation mode to the other, in response to predetermined tones and timed pauses. According to the signalling scheme, if an analog modulation mode is desired, the paging system encoder generates a high-level guard tone signal for a predetermined interval. The high-level guard tone is immediately followed by a function tone signal. An analog paging signal can immediately follow the function tone signal.

If a binary modulation mode is required, the paging system encoder sends a high-level guard tone for a predetermined interval followed by a function tone. The paging system then pauses for a predetermined period of time and begins transmission of a binary comma signal which causes the paging base station to transfer to the binary mode. If an analog signal is to be sent after a binary transmission, the paging system pauses for a predetermined period of time and then retransmits the high-level guard tone signal. The analog paging signal can immediately follow the high-level guard tone signal and a transmission of the function tone signal is not required.

If the paging system is to make a transition from a an analog to binary modulation mode, the paging system encoder generates a pause for a predetermined length of time and then begins transmission of the binary signal. Retransmission of the high-level guard tone and function tone signals is not required.

It therefore is an object of this invention to provide an improved encoder and decoder which rapidly instructs a paging base station to key in an analog or binary modulation mode.

It is another object of this invention is is to provide a encoder and decoder which allows a paging base station to switch from an analog to a binary modulation mode without first dekeying the transmitter in order for the base station to make a transition from one transmission state to the other.

It is still another object of this invention to provide a paging base station remote control system which improves the volume of paging messages a paging system is capable of processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are block diagrams of two paging systems of the type which embody the signalling scheme of the present invention.

FIGS. 2a-2f show specifically formatted a signalling scheme for a communication link between a paging terminal and a paging base station.

FIG. 3 is an electrical schematic of an encoder which generates the required signalling to the paging base station.

FIGS. 4 through 14 are flow diagrams which define the operation of the microcomputer used in the encoder of FIG. 3.

FIG. 15 is an electrical schematic of a paging system decoder which decodes the signalling scheme illustrated in FIG. 2.

FIG. 16 is an timing diagram showing the function of the paging system decoder of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a block diagram of a paging system of the type which embodies the signalling scheme utilized in the present invention. The illustrated paging system includes a paging terminal (10) adapted to provide analog or binary paging signals. The paging terminal interfaces with a modem 12 and a paging system encoder 14. The modem 12 is a conventional device which converts a binary signal from the paging terminal 10 to a frequency-shift keying (FSK) signal used by the station encoder 14. The paging terminal 10 cooperates with the paging system encoder 14 by providing signals to the encoder 14 which indicate that the paging terminal 10 is about to transmit binary or analog signals. The encoder 14 then signals the paging terminal 10 when the encoder is ready to receive either type of signalling. An exact description of the paging terminal and the interface signals required by the paging system encoder are described in Motorola document 68P81063E15 (1982) entitled "Simulcast System Controller and PURC Station Controller" available from the Service Publication Department of Motorola, Inc., 1301 East Algonquin Road, Schaumburg, Ill., or from Motrorola C & E Parts, 1313 East Algonquin Road, Schaumburg, Ill.

The encoder 14 then generates a series of tones and timed pauses which are especially formatted and communicated to a paging base station which includes station decoder 16. The decoder 16 converts the formatted signals from the encoder 14 and selectively activates modem 18 and transmitter 20 in predetermined timed sequences as determined by the signals from the encoder 14. The paging transmitter 20 can then be selectively switched between analog or binary modulation modes in response to the signalling scheme of the present invention.

The paging system encoder and decoder can be connected in several ways. FIG. 1a shows an encoder and decoder being connected through a terrestrial wire-line. Referring now to FIG. 1b, the paging system encoder and decoder can also be connected through a communications link provided by a radio link transmitter 22 and a radio link receiver 24. In addition, the paging system signalling scheme can be expanded to control any number of simulcast paging transmitter remote sites 26, as shown in FIG. 1b. The paging system encoder and decoder are further described in copening patent applications entitled PAGING UNIVERSAL REMOTE CONTROL ENCODER AND PAGING UNIVERSAL REMOTE CONTROL DECODER by Dunkerton et al, patent application Ser. Nos. 487,490 and 487,488 respectively and assigned to the assignee of the present invention.

The signalling scheme shown in FIG. 2 has been developed to unify the base station control functions required in paging systems utilizing both binary and analog signalling. Most commonly, the analog signalling is in the form of sequential tone signalling. For the base station there are three modes of operation: (1) binary (FSK signalling), (2) audio (sequential tone signalling or tone and voice signalling), and (3) combinations of both binary and audio signalling.

Control of the paging base station is accomplished from paging terminal 10 which operates in conjunction with the paging system encoder 14 and is located either remotely or locally with respect to the paging transmitter 20. FIGS. 2A through 2F show that the station control sequence is preferably initiated by a high level guard tone of 2175 Hertz for a period of 120 to 140 milliseconds followed immediately by a 40 millisecond tone F1 of 1950 Hertz. These two sequential tones are transmitted by the encoder 14 and are intended to signal the base station to turn on its transmitter in preparation for transmitting a binary or analog signal to a pager unit. The pager base station need only be rekeyed if more than 350 milliseconds have lapsed since the last transmission.

A combination of binary data and analog data transmission is required for paging systems with mixed binary and tone signalling or tone and voice pagers which use binary signalling. The timing scheme in FIGS. 2A through 2F allows interactive analog and digital paging without dekeying the transmitter. FIGS. 2A through 2F show the time spacing of analog and binary signals that are preferred for the paging base station to respond appropriately. In FIGS. 2A, 2B, 2D and 2E it can be seen that for transmission of a binary signal after a high level guard tone-function tone is sent, a pause of 130 to 150 milliseconds is preferably inserted into the transmission before sending the binary data. The pause of a 130 to 150 milliseconds tells the decoder at the paging base station that there is no analog data and it allows transfer to a binary modulation mode upon receipt of binary data.

If analog data is to be sent immediately following a binary data transmission, a pause of 50 milliseconds is inserted between the end of the binary data and the beginning of the high level guard tone signal (G1). This insures that the paging base station has sufficient time to return to a condition in which it can sense a high level guard tone. Note in FIG. 2A that after the binary data has been received and transmitted by the paging base station and a pause of approximately 50 milliseconds has elapsed, only the high level guard tone need be transmitted to the paging base station to enable the paging base station in a analog modulation mode. The function tone is no longer necessary since the paging base station has been keyed previously and insufficient time has elapsed between pages to cause the base station to dekey.

Referring to FIG. 2A, a remote or local terminal transmits to a paging base station a guard tone function tone sequence G1, F1 to instruct the base station transmitter to key. After the guard tone-function tone sequence has been transmitted to the paging base station and has been received by it, the paging base station is immediately in a modulation mode that is appropriate for analog data. FIG. 2C illustrates this condition. Binary data is sent only after a 130 to 150 millisecond pause after the guard tone-function tone sequence. Binary data is sent to the base station via a modem 202 format (1200/2200 Hertz signalling) which is well known. Audio data may be sent immediately after the guard tone-function tone sequence along with a low level guard tone.

To initiate an analog modulation mode, a pause of approximately 50 ms follows the termination of the binary data transmission before the high level guard tone is again transmitted. Immediately following the second high level guard tone, the analog data (in this case a voice) is sent to the base station along with low level guard tone (not shown). A binary turn-off code ends the transmission to the binary pager and follows the voice message after a 130 to 150 millisecond pause in order for the paging base station to know that it may transfer to a binary modulation mode for the turn off code.

FIG. 2B shows the transmission of a binary only page. The base station is again keyed by a high level guard tone-function tone sequence. The appropriate 130 to 150 millisecond pause then follows the function tone. The pause tells the paging base station that there is no analog data and it may transfer to a binary modulation mode in anticipation of the binary data. The paging base station then receives the binary data after it has transferred to its binary modulation mode.

FIG. 2C shows the timing scheme for a sequential tone page. The high level guard tone-function tone sequence again keys the base station. This time the analog information is immediately transmitted after the function tone since the paging base station is in an analog modulation mode immediately following the function tone. Once analog information is received in the time period immediately following the function tone, the paging base station will stay in an analog modulation mode until it receives a 130 to 150 millisecond pause.

FIG. 2D shows a binary page followed by a sequential tone page. The first portion of the signal stream is the same as shown in FIG. 2B. After the binary data has been sent and received by the paging base station, a pause of about 50 milliseconds is inserted into the transmission stream to enable the paging base station to condition itself to receive a high level guard tone. The high level guard tone is transmitted from the paging system encoder and received by the paging base station. The paging base station immediately goes to an analog modulation mode and modulates the analog data which is immediately received after the high level guard tone.

FIG. 2E shows the signalling for multiple binary pages sent without pause. The timing scheme for multiple binary pages is essentially the same for a single binary page as shown in FIG. 2B. Binary data is simply sent one after the other without pause after the initial 130 to 150 millisecond pause.

FIG. 2F shows a sequential tone followed by a binary page. Again, the high level guard tone-function tone sequence keys the paging base station transmitter and also causes the paging base station to enter an analog modulation mode. The analog data is transmitted from the terminal immediately following the function tone and thus the analog data is appropriately modulated. The binary data is sent only after the completion of the analog data and a 130 to 150 millisecond pause.

In the preferred embodiment, the analog signal from the terminal is summed with a control tone that is preferably the same as the high level guard tone, only at a reduced amplitude.

In summary, to enable the binary mode after the high level guard tone-function tone sequence has been transmitted, a puase of 130/150 millisecond duration is inserted before sending the binary signal. If multiple binary pages are to be transmitted, the binary data identifying each pager should be sent in sequence without pause. Upon completion of the transmission of the binary information, approximately 50 millisecond pause must be sent before enabling the audio control in the paging base station. After the 50 millisecond pause, a high level guard tone is sent to the paging base station to enable the analog-audio mode. (Note: No function tone is needed after the initial station control set-up). If the paging base station does not receive a signal for a period of 350 milliseconds, the base station will automatically dekey.

If a binary signal is to be transmitted following an analog/audio signal, the sequence described above must be repeated. That is to say, 130 to 150 millisecond pause must follow the guard tone before the binary data is delivered to the pager base station.

FIG. 3 is an electrical schematic of an encoder which can generate the required signalling scheme of the present invention. A more detailed electrical schematic of the encoder circuit of the present invention is illustrated in Motorola document 68P81063E15 entitled "Simulcast System Controller and PURC Station Controller," available from the Service Publication Department of Motorola, Inc., 1301 East Algonquin Road, Schaumburg, Ill., on from Motorola C & E Parts, 1313 East Algonquin Road, Schaumburg, Ill. In accordance with the present invention, the various paging output terminals are provided to the respective binary, audio and voice input terminals of the paging system encoder. The signals are interfaced through transformers 102, 104 and 106 respectively, which provide impedance matching end isolation between the paging terminal and the paging system encoder. The transformers 102, 104 and 106 are then connected to buffer amplifiers 108, 110 and 112 which compensate for gain losses in the binary modem tones, paging tone and voice audio signals. The amplifiers 108 and 110 are connected to variable resistors 114 and 116 which provide further compensation between the various paging signals. It is desirable to adjust the binary modem tone, audio paging tones and voice audio tones so they are substantially equal in amplitude when they are connected to summing amplifier 126. The amplifier 112 is connected to a premphasis network 122 which conditions the voice audio signal and provides a standard frequency shaping used to transmit paging voice audio to remote paging transmitters. The premphasis network is then coupled to an amplifier 128 and a variable resistor 130 to compensate for gain variations in this signal path. The amplifier 128 also includes a notch filter to remove the guard tone frequency. The variable resistors 114, 116 and 130 are then coupled to electronic mute switches 118, 120 and 124. Mute switches 118, 120 and 124 can be any type electronic switch adapted to pass an electrical signal in response to an electrical control signal. The mute switches 118, 120 and 124 are coupled to a peripheral interface adaptor circuit (PIA) 132.

The outputs of mute switches 118, 120 and 124 are coupled to a summing amplifier 126 which combines the various signals in equal proportions. The summing amplifier is then coupled to an output amplifier 134 which is coupled to a transformer 136. The amplifier 134 and transformer 136 convert the output signal of summing 126 to a signal of amplitude and impedance required by the wire-line hookup or transmitter link used to couple the paging system encoder 14 to the paging system decoder 16.

The summing amplifier 126 also receives an input from the variable resistor 138 which is coupled to a programmable attenuator 140. The programmable attenuator 140 is coupled to two control signals from the peripheral interface adaptor 132 and a tone input from the low pass filter 142. The low pass filter 142 is coupled to a microcomputer 144. The microcomputer 144 generates the various control tone sequences of the paging system encoder and provides signals to the programmable attenuator 140 through PIA 132 to control the amplitude of the control tones coupled to the summing amplifier 126. The microcomputer 144 and the PIA 132 also control the operation of the mute switches in response to several input signals in accordance with the signalling scheme of the present invention. The present invention utilizes a widely used microcomputer integrated circuit designated MC6803 and available from Motorola, Inc. The companion peripheral interface adapter integrated circuit is designated MC6821 and is also available from Motorola, Inc.

The paging system encoder 14 is configured to provide direct user control via several switches, 146 through 162, which are disposed on a panel which is accessible to the user of the encoder. The switches 146, 148, 150, and 152 are connected to input ports of the PIA 132. Switch 146 when closed will cause the paging system encoder to enable the tone, modem and voice paths to be enabled simultaneously to the output terminal transformer for audio level set. Likewise, switch 148 when closed will cause a series of audio test tones, generated by microcomputer 144 to be placed at the output terminals of the encoder. Switches 152 and 150 are included with the paging encoder circuit to allow the paging system to accommodate additional RF link transmitters to be used in a simulcast system. For example, if a paging transmitter site is located a large distance from the paging terminal site, a repeater site will be included in the system. Each repeater site will require a certain amount of time to allow the repeater transmitter to key and therefore the high level guard tone must appear for an extended time to allow retransmission to the paging transmitter site. Each link site requires approximately 250 ms to retransmit the high level guard tone. Switches 150, 152 and configured to provide a binary encoded input to the encoder circuit which activates an additional guard tone period to be generated by the paging encoder. The high level guard tone signal can be increased in 300 ms increments, and a maximum of 1200 ms can be effected by switches 150, 152. If both switches 150 and 152 are open, no high level guard tone will be added to the normal tone sequence. If switch 150 is open and switch 152 is closed, 300 ms of high level guard tone will be added to the initial tone sequence. Likewise, increments of 300 ms can be added to the high level guard tone sequences by providing the various combinations of switches 150 and 152.

The paging system encoder circuit cooperates with the paging terminal 10 of FIG. 1, through the clear to page voice terminal 162, the clear to page binary terminal 160, the key analog terminal 156 and the key binary terminal 158. In operation, a paging subscriber will activate the paging terminal 10 of FIG. 1, through a telephone link by signalling the telephone number assigned to the unique pager address. The paging terminal 10 will then convert the telephone number to a signal comprising the exact pager address. The paging terminal 10 then signals the paging system encoder that a paging signal is imminent by activating either the key analog terminal 156 or the key binary terminal 158 depending on the type of paper being signalled. If the key binary terminal is activated, the paging encoder will generate the series of timed tones and pauses which place the paging remote transmitter site in the binary transmission mode. When the transmitter has been properly set up and keyed, the paging system encoder will activate the clear to page binary terminal, and activate the binary modem tone mute switch 118 to pass modem tones to summing amplifier 126 and output transformer 136. Similarly, if the system is to be placed in the analog audio transmission mode, the paging terminal will activate the key analog terminal 156 and the paging system encoder will generate the series of timed tones and pauses which place the paging remote transmitter in the analog transmission mode.

FIGS. 4 through 16 are flow diagrams which define the operation of the microcomputer 144 used in the encoder of FIG. 3. FIG. 4 details the operation of the initial program sequence when power is first applied to the paging encoder. Since it is not possible to predict a specific logic condition which will be present at any particular input or output terminal of the microprocessor or PIA, the power-up sequence of FIG. 4 establishes known conditions on all critical input and output terminals.

When power is first applied to the paging encoder 14, the program control of the microcomputer is configured to execute an initialization program 200. The program control then proceeds to item 202 and immediately sets the microcomputer interrupt mask which insures the program will not be interrupted during the power-up sequence. The program then initializes all random access memory variables.

The microcomputer 144 ports can be configured to function as either inputs or outputs to the microcomputer and must be configured according to program control. As noted in FIG. 3, the microcomputer 144 acts as the tone sequence generator for the paging system encoder. Any tones which may be present at microcomputer port P2 of FIG. 3 are shut off during the power-up sequence 200 by designating port P2 as an input. This step insures no tones are placed on the output of the encoder circuit until necessary.

The microcomputer 144 provides an internal tone generator which is controlled according to the state of an internal register. By entering a numerical value in the timer control and status register, a corresponding tone period will be generated by the tone circuit. According to the next item 206, the timer control and status register are initialized and subsequently, an arbitrary number is loaded into the TCS register.

The power-up sequence next designates the PIA ports as input or outputs.

Referring now to FIG. 3, signals KA, KB, HO1, HO2, TT and OA are coupled to PIA port A. Likewise, signals CTPA, CTPB, M0, M1, M2, M3, AT1, AT2 are coupled to PIA port B. In accordance with the present invention, FIG. 4 shows the PIA port configuration. Consequently, item 210 configures PIA port A as an input and PIA port B configures as an output. The power-up sequence next initializes the values associated with PIA port B by placing the code on the PIA port B 218 which corresponds to opening or inhibiting all mute switches 118, 120, 124, 125 of FIG. 3, inhibiting the clear to page signals 160, 162 of FIG. 3 and by adjusting the programmable attenuator 140 of FIG. 3 for maximum attenuation.

The paging system encoder makes decisions as to what subsequent actions to effect based on two integral system status Bytes which are an indication of the system's past and present activity. The system status bytes are designated New Status (NSTAT) and Old Status (OSTAT). Since the system operation will be affected by the old system status, for instance, an analog to binary transition, this byte must be initialized during the power-up sequence. Item 220 sets the system status byte OSTAT to a code comprising all binary ones, which indicate that the system is currently dekeyed.

The paging system encoder is now configured with initial conditions in critical areas which will ensure correct system operation. Subsequently, the interrupt mask is cleared 222, thus allowing the microprocessor to execute interrupt commands. Timeout period 224 is provided to allow all initial conditions on the system to stabilize. The paging encoder now enters the SCAN mode 300.

Referring now to FIG. 5, there is illustrated a flowchart embodying the scan method of the present invention. The flowchart in FIG. 5 provides a detailed description for the process steps necessary for implementing the scan method of the present invention in the paging system encoder 14 in FIG. 3. The scan routine forms the basic background operating scheme of the present invention. The primary task for the scan routine interprets key input commands from either hardware front panel switches or from the paging terminal and exits to one of five tasks, depending on the condition of the key switches.

When the scan routine is activated, item 302 retrieves the system status bits D6 from the system status bytes NSTAT and OSTAT.

Referring now to decision 306, if both system status bytes NSTAT and OSTAT show a binary 1 in D6, which is an indication of the hardware panel key switch, then the system is dekeyed, and program will enter item 304. If either data bit D6 from NSTAT or OSTAT is a binary zero, the hardware panel key switch has been changed and the program will enter the panel key handler (PKHNDL) routine 308. Item 304 retrieves the system status bits D1 and D0 from the system status bytes NSTAT and OSTAT. Status bits D0 and D1 of NSTAT indicate whether the paging system encoder is being signalled, that is, either an analog or binary paging signal is imminent from the paging terminal 10 or modem 12 of FIG. 1. Decision 310 then compares system status bits D1 and D0 which indicate if a key command has been received from the paging terminal. If NSTAT has not changed from the previous period OSTAT, the program returns to the initial item of the scan routine and continues searching for a change.

If NSTAT has changed, the system will enter item 316, which provides a 5 ms time delay. This time delay provides enough time to detect a key bounce or an erroneous input. Decision 318 compares the key bit D0 or D1 with the state of the key bit D0 or D1 5 ms earlier. If a key bounce is detected, decision 318 returns program control to the first step of the scan routine.

If a key bounce was not detected, the program proceeds to decision 320 which examines the D0 and D1 status bits in the OSTAT status byte. If the D0 and D1 status bits show 00, which is an impossible condition at this point in the program, the program control will exit decision 320 and proceed to error routine 334. If an error is not detected, the program proceeds to decision 322. If the system has been previously keyed in either the analog or binary mode, the program will proceed to decision 326. If the system was not previously keyed, the program will exit the scan routine and proceed to the select modulation (SELMOD) routine 370, which will be discussed in more detail later.

As noted previously, if the paging system has been previously keyed, the program will proceed to decision 326. At this point, the paging system will either dekey or change transmission modes.

If the system status bits D1D0 of NSTAT and OSTAT indicate the sytem was previously keyed and is now required to dekey, the program will proceed to the dekey routine 330. Alternatively, if the system status bits D1D0 of NSTAT and OSTAT indicate the system should remain keyed, but in another mode, the system will enter the modulation change routine 328.

The modulation change routine 328 occurs in mixed paging systems when binary pages are sent immediately after a tone-signalled page or vice versa. As previously discussed, mode information is carried on the system status bits D1D0. Item 352 retrieves the NSTAT status bits D1D0. Item 552 compares the NSTAT status bits with the OSTAT status bits. If the NSTAT status bits D1D0 are both equal to binary zeros, a race condition or overlapped key request is indicated. Decision 354 will then pass program control to item 356 which will then update the NSTAT status byte to the current value of OSTAT and subsequently select the statlus update routine (REPOLL) 346.

If either NSTAT or OSTAT contains a binary one in D1D0, the program will proceed to decision 360. If the OSTAT status bits D1D0 show 10 and the NSTAT status bits show 01, an analog to binary transition is indicated, and decision 360 will select the AUDBIN routine 362, which will be discussed in more detail later. If AUDBIN is not selected, the Program will program to decision 364. If the OSTAT status bits D1D0 show 01 and the NSTAT status bits show 10, decision 364 will select the binary to analog transition routine (BINAUD) 368. If BINAUD is not selected, an error has occurred and decision 364 will select the error routine 334.

If the error routine 334 is selected, Item 332 will reset the NSTAT status byte value to the normal value (D1D0=11) indicating the system should be dekeyed. The Item 332 then selects the dekey routine 330.

When invoked, dekey routine 330 will execute the tasks required to dekey or turn off the paging transmitter stations and reset the paging encoder 14 for the next key-up sequence. The dekey routine begins with item 338 which designates microcomputer port P2 of FIG. 3 as an inut, thus turning off any tone appearing on the port. The program proceeds to items 340 and 342 which updates the PIA port B bit status instruction so that the audio mute switches 118, 120, 124 and 125 of FIG. 3 are set to mute the signal paths, and so that the programmable attenuator is set for maximum attenuation. The program proceeds to item 344 which provides a waiting period required by the paging system to dekey. Item 344 then proceeds to the REPOLL routine 346. This routine is the end of the background loop. It updates the current status of the paging system encoder. Item 348 replaces the contents of the OSTAT register with the NSTAT status values, and then returns the program to the beginning of the SCAN routine 300.

Referring now to decision 322, if the system status bits indicate a key-up condition, the program will proceed to the modulation selection routine, SELMOD, routine 370. FIG. 5b shows the program sequence for SELMOD. The SELMOD routine 370 selects one of two sequencing tasks to be performed by the paging system encoder, depending on the system status bits D1D0 which indicate the key analog and key binary signals of the paging terminal. Item 374 reads the NSTAT status bit for any keying activity. If both status bits D1D0 are binary zeros, a race condition is indicated, and decision 376 will select Item 378 giving binary priority if both analog and binary key requests are simultaneous. Item 378 will update the NSTAT variables D1D0 to a 01 condition and select the key bin routine 386.

If the NSTAT variables D1D0 show a non-zero condition, a decision 376 will select decision 380. If the system status bits D1D0 indicate an analog page, decision 380 will select the KEYAUD routine 382. If KEYAUD is not selected, the program will select decision 384. If the system