Programmable Paging Encoder

This invention relates to a paging encoder which utilizes a microcomputer to produce two-tone sequential or five-tone codes which are transmitted via an associated transmitter to portable telephone paging receivers.

Traditionally, paging encoders have been bulky, expensive, desk bound units suffering from limited capacity and a lack of adaptability which would allow operation across the spectrum of different selective signalling formats.

Incompatibility between signalling formats of the various paging systems creates a severe handicap on prior art systems because numerous formats are currently employed. The most popular are: the Motorola two-tone, Motorola five-tone, Motorola six-tone, General Electric two-tone (Type 99), and Reach two-tone signalling formats.

Attempts have been made to provide paging encoders which are capable of operating within the requirements of the various signalling formats, but such systems have been expensive to design and fabricate due to the numerous differences between the various formats.

For example, Motorola utilizes one second for the first tone, two to three seconds for the second tone, and requires seven to eight seconds for group calls. The system employs six reed groups of ten tones each, which permit about 870 codes in the basic tone pairing scheme and approximately 3,500 tone pairs in an extended assignment plan.

General Electric employs a 1-second first tone and a 1.5-second second tone, and does not allow for any group call. Instead it provides an extra tone, known as the diagonal tone, to replace the first tone of any identical tone pair. This occurs in pager codes employing a 0, 2, or 4 as the first number of the cap code. Incorporated in their code plan are three reed groups of ten tones each plus one diagonal tone that allows them to generate 900 different codes.

The Reach system features both fast and slow two-tone sequences. They have a wider frequency spread between their tones to facilitate high-speed encoding. Their high-speed tone timings are running about 100-150 milliseconds for both tones. The slower format employs a 2-second first tone and a 700-millisecond second tone. This slower scheme works in conjunction with their battery-saving feature to permit up to a year's operation between battery changes. Reach uses a single tone of 5 seconds duration to initiate group call. The Reach format incorporates a total of 60 tones. However, only tones 11-55 are used for two-tone selective calling and that permits 1000 codes.

Motorola uses a totally different strategy in its five- and six-tone decimal digital pager. Rather than selecting two tones from a large range of frequencies to generate all of the tones needed in a high capacity system, Motorola elected to use a new technique that allows the pagers to generate from 100,000 to 1,000,000 codes using only 12 tones. The straight five-tone address will produce 100,000 calls while adding 10 different preambles ahead of each address would accommodate 1,000,000 codes. This 1,000,000 code capacity would apply only to pagers with the battery-saving option that relies on the correct preamble to wake it up.

The basic signalling scheme used in the five-tone sequence consists of an optional 690 millisecond preamble tone followed by a 45-millisecond gap of unmodulated carrier, then five sequential tones each of 33 milliseconds in length and either a 52-millisecond gap (five-tone) or 52 milliseconds of special tone X (six-tone).

The X tone is used to activate the uninterrupted tone in the dual-address pagers instead of the normal pulsating tone that results from a five-tone address. Twelve frequencies are used to represent the digits 0-9, repeat tone R, and special tone X. The repeat tone is substituted each time there are two identical, successive digits appearing in the address code. For example, an address code of 25597 would be converted to 25R97. The preamble can be set to any one of the 10 tones 0-9, or can duplicate the first number in the address code.

In addition to all the different format problems, it is difficult to make any code assignment changes within the same format. For example, in the Motorola expanded code assignment plan, there are over 20 different cap code prefixes producing 180 group combinations (Motorola Pager Manual Table 3). Most encoders are capable of handling only one of the 20 combinations at a time, if that many. In earlier units, it was necessary to change reed banks in order to change from one code assignment to another.

In view of the preceding, it is a primary objective of the present invention to provide a paging encoder capable of easily changing formats, code assignment plans and preambles.

A further object of the present invention is to provide a paging encoder capable of easily changing formats, code assignments and preambles which is small and inexpensive and highly stable and reliable.

A still further objective of the present invention is to provide a paging encoder as suggested above which is capable of operating from a battery power source having a wide voltage range.

Another objective of the present invention is to provide a miniaturized paging encoder that can be used in combination with a portable transmitter such as a walkie-talkie or a mobile unit.

A still further objective of the present invention is to provide a paging encoder having wide format capabilities adaptable to function in any of the standard encoding systems.

Another objective of the present invention is to provide a paging encoder adaptable for combining with a signal generator to provide a testing system for paging receivers.

Another objective of the present invention is to incorporate microcomputer technology to create a miniaturized paging encoder capable of easily changing formats, code assignment plans, and preambles.

Another objective of the present invention is to provide a paging encoder utilizing microcomputer technology in combination with energy conservation means adapted to keep the microprocessor and associated electronics in an off state except during periods when encoding operations are being performed.

A still further objective of the present invention is to provide a microcomputer controlled paging encoder capable of providing encoding compatible with any of the below listed systems in response to positioning of a simple switch or jumper cable system:

Motorola Two-Tone Basic 870 Call

Motorola Two-Tone Expanded Code Plan

Tororola Five-Tone (No Preamble)

Motorola Five-Tone With X Tone and No Preamble

Motorola Five-Tone With Preamble

Motorola Five-Tone With X Tone and Preamble

Reach (High Speed)

Reach (Low Speed)

General Electric (Type 99)

The preceding, and other objectives of the present invention will become apparent in light of the specification, drawings and claims which follow.

The paging encoder disclosed herein employs a microcomputer to generate all the tones and timing requirements required by any of the paging encoding schemes in use.

The microcomputer of the paging encoder is programmed with a look-up table containing all of the code formats, while specific system formats are selected by either a series of jumper interconnections or a multiple contact switching arrangement. A keypad code entry automatically turns on the microcomputer and enters the desired code into the computer system which then converts it to the proper format and delivers it to an output means coupled to a compatible transmitter.

In addition to providing a properly encoded output signal, the microprocessor provides a lock-on function that maintains power to the system during the encoding function and disconnects the system from the power source at the completion of the encoding operation to conserve the power source.

Additional features of the system provided by the microprocessor are annunciating side tones for audible feedback and a push-to-talk enable function, both of which function in conjunction with the associated receiver transmitter. The push-to-talk enable function activates the transmitter and maintains the transmitter in an on-state for a period of time long enough to allow the generated code to be transmitted plus a brief additional period during which time an operator may add a verbal message.

The single drawing of this patent is a schematic representation of a preferred embodiment of the subject paging encoder illustrating the inputs, outputs, and supporting functions of the microprocessor.

Any of the large variety of microcomputers may be adapted to function in the present invention. However, for explanatory purposes a typical circuit describing the invention is presented hereby which utilizes a single chip microcomputer of the 8048 series. The integrated computer circuit and its associated operational and controlling circuits is illustrated in the FIGURE. The program required to adapt the microcomputer to perform the required functions is presented at a later point in this specification.

In its quiescent state, the paging encoder illustrated in the FIGURE is off. A voltage source in the range of 7 to 8 volts is applied at input pin 11 and coupled to a voltage regulator 12 which produces a regulated 5.6 volt output. Transistor Q13 which in the exemplary system is a type MPSA65, is normally off and the voltage distribution point VDD 14 for the system is at 0 volts. When one of the keys on keypad 15 is depressed, it provides a ground connection to the base of transistor 13 and this turns on the transistor and couples the 5 volt regulated power source 12 to the power distribution point VDD 14.

The keypad 15 may be any of a large number of available keypads such as the 12 button Digitran or Chomerics. In the preferred embodiment disclosed, a Digitran type keypad incorporating three light emitting diodes colored Red, Green, and Yellow is used. However, any keypad capable of being coupled to a system to provide a ground upon key activation may be utilized.

When transistor 13 is energized and a positive 5 volts is available at the voltage distribution point 14, the Red LED indicator 16 is energized to signify that the system is on and the microcomputer 10 is energized via input pin 40. Once energized, the microcomputer 10 provides a positive voltage level at pin 35 for a predetermined period of time. This positive voltage is applied to the base of transistor 17 and turns that PN2222 transistor on which, in turn, maintains transistor 13 in the conducting state to lock-on the power distribution circuit to keep the microcomputer 10 energized. A delay means is included in the microcomputer system which terminates the positive voltage at pin 35 after a predetermined delay period calculated to enable completion of the encoding processes after activation of the last digit via keyboard 15. Optional capacitor 40 provides a time delay which continues to allow activation of the transmitter via transistor 33 after removal of the output on pin 36 for a period of time which will enable an operator to transmit an additional message after the encoded signal. After the time delay, with the positive voltage level on pin 35 of microcomputer 10 removed, transistor 17 turns off, and transistor 13 turns off disconnecting the positive VDD voltage from the microcomputer and associated circuitry until such time that a key on keypad 15 is again activated.

In addition to turning on the power distribution system, keypad 15 provides a means to selectively apply ground potential to pins 12 through 18 of the microcomputer. When the computer is energized, these pins are normally at a positive potential due to their connection to a resistive network comprised of 100 K resistors to the regulated 5 volt distribution network. A ground input on pins 12 through 18 of the microcomputer 10 is interpreted by the microcomputer as a 2 out of 7 code forming one of the digits identifying a paging receiver to be alerted. When the complete paging receiver identifier has been entered into the microcomputer 10 via keypad 15 and input pins 12 through 18, a properly encoded pulse train comprised of square waves is applied to output pin 38 of the microcomputer 10. The type of encoding performed by microcomputer 10 is a function of selector switch 18 which selectively grounds pins 21 through 24 and 27 through 31 of microcomputer 10. In an alternate embodiment, the switch system may be replaced by jumper wires, but in either case selected pins are coupled to ground to cause the microprocessor to encode in accordance with a desired system format. Listed in the table below are the jumper connections or switch positions required by the exemplary system presented herein to enable the paging encoder to produce the indicated system formats. In the chart, a 0 indicates that the indicated pin of microcomputer 10 is open and a 1 indicates the pin is connected to ground.

When the system is functioning in any one of the Motorola five-tone formats, depressing the * on the keypad will cause the system to select an X tone regardless of the condition of pin 21 of the microcomputer.

When microcomputer pins 21, 22, 23 or 24 have been connected to select a Motorola code assignment, the below listed chart indicates the ground or open status that should be maintained on microcomputer pins 27 through 31 to select the 20 Motorola prefixes.

When microcomputer 10 pins 21, 22, 23 or 24 have been connected to select a Motorola five-tone format, the following chart indicates the connection of microcomputer pins 27 through 31 for selection of different preambles.

In accordance with the setting of switch 18 or the substitute jumpers therefore and the digits keyed in on keypad 15, computer 10 outputs on pin 38 the appropriate tones as square waves which are processed by the differentiator comprised of C19 and R20. This differentiator accentuates the highs in the output signal to compensate for their attenuation in the following low pass filter comprised of R21 and 22 and C23 and 24. This filter produces a triangular wave which is a pseudo sine wave. An additional capacitor, capacitor 25 is coupled to ground in parallel with capacitor 23 by computer 10 when the output is below 900 Hz to increase the roll off on the low frequencies. This provides better filtering at the low frequencies and stabilizes the output by compensating for the increased filtering of the higher frequencies. This eliminates most of the third harmonic distortion and the resultant sine wave controls condition of output transistor 26. In the illustrated embodiment, this transistor is a type PN2222 and the emitter is coupled to ground via a 1 kilohm potentiometer 27 with the output taken off of the variable potentiometer tap. This output is applied through a capacitor 28 to the low impedance output 29 and through resistor 30 to high impedance output 31.

Whenever a key on the keypad 15 is depressed, the computer 10 provides a chirp tone output at pin 37 to output jack 32 which may be connected to an annunciator such as the speaker of the receiver transmitter to which the encoder is coupled. This feature is to provide an audio indication of key actuation.

When the computer 10 has received the input from the keypad and prior to its commencing to output the resultant encoded data, pin 36 does high and causes transistor 33 to become conductive. This energizes the push-to-talk switch or relays in the associated transmitter via jack 34 and also provides a path for current flow through light emitting diode 35. In a preferred embodiment, this diode is the Green diode on the keypad and it indicates that an encoded signal is being transmitted.

The output or high level at pin 36 occurs approximately one-half a second before the encoded tones are provided at pin 38 of computer 10 and it lasts until power is disconnected from the computer as a function of removal of the high voltage level at pin 35 as previously discussed.

Capacitor 36 provides a delay function which prevents the computer 10 from becoming activated upon the application of the regulated 5 volts until the capacitor charges. There's an internal resistor within the computer that creates a voltage drop that causes this capacitor to require approximately 20 milliseconds before it enables the computer to power up.

Diodes are incorporated in the circuit to provide isolation for the power control circuit to ensure that the power control circuit will not affect the operation of the codes entered into the computer and to further ensure that operations within the computer will not adversely affect the operation of the power control system.

Normally closed push-button switch 38 grounds pin 32 of the microcomputer 10. When pin 32 is grounded, the push-to-talk function at pin 36 is withheld by the microcomputer 10. Depressing switch 38 removes the ground connection from pin 32 and allows the push-to-talk enabling signal to be applied to the transmitter and the encoded paging signal to be presented on output pin 38.

Grounding pin 33 of microcomputer 10 causes a 250 millisecond gap to occur between the first and second tones in the Motorola and General Electric two-tone formats.

Timing within the microcomputer 10 is controlled by a 3.58 MC crystal 39 connected across pins 2 and 3.

In the exemplary system presented herein, the microcomputer 10 is a standard type 8048 microcomputer programmed in accordance with the following instructions: ##SPC1## ##SPC2## ##SPC3## ##SPC4## ##SPC5## ##SPC6## ##SPC7## ##SPC8## ##SPC9## ##SPC10## ##SPC11## ##SPC12## ##SPC13## ##SPC14## ##SPC15## ##SPC16## ##SPC17## ##SPC18## ##SPC19## ##SPC20##

While preferred embodiments of this invention have been illustrated and described, variations and modifications may be apparent to those skilled in the art. Therefore, I do not wish to be limited thereto and ask that the scope and breadth of this invention be determined from the claims which follow rather than the above description.