GB2289189A - Method for selective connection of a data processor to a telephone line or radio telephone - Google Patents

Abstract

An interface and cable, has a standard telephone jack connector (210) which connects to either a telephone line or a radiotelephone. The standard telephone jack connector allows use of a conventional telephone cable between the data modem and a telephone line. When connection to a radiotelephone is desired, a special cable (320) for the radiotelephone connects to the joint connector. A detection circuit 250 senses signals received at the joint connector to determine whether the joint connector (210) is coupled to the telephone line or the radiotelephone. A control switch (240) configures the data modem for the telephone line or for the radiotelephone based on the determination. <IMAGE>

Description

METHOD AND APPARATUS FOR SELECTIVE CONNECTION TO TELEPHONE LINE OR RADIOTELEPHONE Background of the Invention 1. Technical Field of the Invention The present invention relates to telephone line and radiotelephone interfaces and, more particularly, relates to a method and apparatus for selective connection through either a telephone line or a radiotelephone.

2. Description of the Related Art Data modems typically connect computers to a telephone line, such as a land line connection. Because telephone lines use a two-wire circuit having full-duplex operation, data modems typically use a hybrid to interface a modulator and a demodulator to the telephone line. This interface through the hybrid is necessary because each of the modulator and demodulator is half-duplex while the telephone line is full-duplex.

The hybrid transforms the half-duplex output of four wires from the modulator and demodulator of a data modem to the two wires of the fullduplex telephone line.

When connecting a data modem over a radio network, such as a cellular telephone network or radiotelephone network, several special problems exist. One problem is that a two-wire, full-duplex output of a data modem cannot be easily transmitted via a radiotelephone. This is because a radiotelephone has separate channels for transmit and receive.

A two-wire, full-duplex data signal would be susceptible to greater error than a half-duplex data signal on each of the separate transmit and receive channels. Radio data modems have thus been built specially dedicated to radio use. These radio data modems have a special connector for connecting directly to, for example, the jack of a radiotelephone.

Data modems are conventionally used in devices such as portable computers or facsimile machines with capability for connection to only land telephone lines. Users of these conventional land telephone line data modems are accustomed to connection of a standard telephone line jack on the data modem, such as an RJ11 connector, to another standard telephone jack, such as an RJ11 connector, on a wall of a building.

Data modems have been recently built capable of selective connection to both telephone lines and radiotelephones. For example, one known facsimile machine has two jacks, one for connection to a land telephone line and another for connection to a radiotelephone. One jack connects via a hybrid to a land telephone line and another jack connects directly to the radiotelephone. An on hook or off hook condition of the land telephone line and of the radiotelephone can be used to separately establish a communication status. However, two separate connectors consume valuable space for cable connection. In a portable computer, a larger door may be required to cover both connectors adding weight and additional cost. Further, separate connectors require extra effort by the user to make a connection.

Another example of a data modem capable of selective connection is provided by a computer modem interface that connects to either a telephone line or a radiotelephone through the same eight pin jack. The user must set up a data connection by indicating the type of connection, to either a telephone line or a radiotelephone. The particular model of telephone may be automatically identified or at least narrowed down by monitoring of data signals. However, connection to either a telephone line or radiotelephone is made by pins on the eight pin connector. Special cables are required for connection from particular pins of the eight pin jack to the telephone line or from other pins to the radiotelephone.

Brief Description of the Drawings FIG. 1 illustrates a cable connecting a modem to a radiotelephone according to the present invention.

FIG. 2 illustrates an interface to a data modem for connecting a telephone jack connector via a cable to a radiotelephone according to the present invention.

FIG. 3 illustrates alternative embodiments of interface to a data modem according to the present invention.

Detailed Description of the Preferred Embodiments Selective connection between a land telephone line and a radio telephone is provided via a single standard telephone jack such as an RJ11 jack or other standard connector used by a given land telephone system.

A user can thus connect the data modem to a land telephone line using the same cable as used by a conventional data modem. When a radiotelephone connection is desired, the user must still use a special cable, but the data modem will electrically recognize a particular connection. The user no longer needs to know to use a special cable for land telephone line connections. And, the user no longer needs to set up, by indicating on a computer keyboard, for instance, the type of connection.

FIG. 1 illustrates a cable 110 for connection between a radiotelephone 120 and a joint connector 155 of a data modem of a computer 130. The cable 110 contains a standard telephone jack connector 150 for connection to a joint connector 155 of the computer data modem.

The cable 110 also contains a radiotelephone connector 140 having a configuration adapted to a particular radiotelephone 145. The joint connector 155 of the data modem is capable of connection to either the radiotelephone 120 or a telephone line, such as a land line telephone jack on the wall in a building. The joint connector 155 preferably is a standard telephone jack connector, such as a RJ11 connector, as specified by the CCITT (Consultative Committee on International Telephone and Telegraph). The joint connector 155 can also be another standard connector, such as RJ45 or other standard telephone jack connector required by a local telephone system or system in a particular country.

The joint connector 155 also could be a unique proprietary connector wherein the same connector would be used for connection from the computer data modem to a telephone line or from the computer data modem to a radiotelephone.

A standard telephone jack connector is preferred for the joint connector 155, because most computer data modem users will connect to telephone lines. These users would prefer the convenience of a conventional telephone jack connection to the telephone line.

FIG. 2 illustrates an interface using a joint connector such as a telephone jack connector 210 for interfacing a computer 220 to a radiotelephone or a telephone line. The telephone jack connector 210 is configured by the interface circuitry for connection to either a radiotelephone connector of a radiotelephone or, instead, for connection to a land line telephone jack on the wall in a building. Modulated and demodulated data is transmitted and received on the same two pins when a telephone jack connector 210 is used in the exemplary embodiment of FIG. 2 according to the present invention. The modulated and demodulated data is transmitted and received over the tip and ring pins, for example, pins 3 and 4 of a standard telephone jack connector 210 such as an RJ11 connector.When the connector 210 is connected to a radiotelephone, other pins, for example, pins 2, 5 and 6, may be connected to control bus lines 281, 283 and 285 of the radiotelephone. Known radiotelephone buses typically require two or three control bus lines. For example, three control bus lines T, R and C can be used by the Motorola three-wire bus as illustrated for instance in U.S. Patent No. 4,369,516.

Other cellular telephones use a different number of lines, typically two lines. The computer 220 may be programmed to directly generate the control data for the radiotelephone, or a custom integrated circuit can be used to generate the control data for the radiotelephone. Because the telephone jack connector 210 is connectable directly to a land line, protection diodes 232,234 and 238 can be provided on control bus lines 281, 283 and 285. These diodes are preferably reverse biased zener diodes having a reverse bias cut-off voltage of about 30 volts to protect inputs to the computer 220, or other integrated circuit.

A cable 320 is provided for connection between the telephone jack connector 210 of the data modem and the radiotelephone connector 310 of a radiotelephone. The cable of this exemplary embodiment preferably has a standard telephone jack connector 150 such as an RJ11 connector on the telephone jack connector end 210 and has a radiotelephone connector 140 configured to a particular radiotelephone 120 on the radiotelephone connector end 310. Protection elements such as reverse bias zener diodes 332, 333 and 334 can also be provided in the cable 320 to protect the control bus lines through the radiotelephone 120. These zener diodes 332, 333 and 334 preferably have a reverse bias breakdown voltage ranging from about 30 volts to about 50 volts.The protection elements protect the control bus lines of the radiotelephone 120 in the event a user mistakenly plugs the standard telephone jack 150 directly into a telephone line. However, the characteristics of the protection element should be more accurately determined based on the input sensitivities of the type or manufacturer of the particular radiotelephone 120 compatible with the radiotelephone connector 140. Each cable 320 should correspond to a particular type or manufacturer of radiotelephone 120 because each cable will have only a radiotelephone connector 140 compatible with that particular type of radiotelephone. For example, a Motorola radiotelephone 120 will only adapt with a Motorola radiotelephone connector 140 and, therefore, the protection elements 332, 333 and 334 appropriate for the Motorola radiotelephone could be included in the Motorola cable 320.

The interface for the data modem has a control switch 240 for selectively connecting modulated and demodulated data to the joint connector of the telephone jack 210 in response to a determination by a detection circuit 250 whether the joint connector 210 is connected to a telephone line or is connected to a radiotelephone. The control switch 240 normally is positioned for connection to a radiotelephone. The detection circuit 250 is preferably a dial tone detector according to the exemplary embodiment of FIG. 2. When the dial tone detector of the detection circuit 250 detects a dial tone, the control switch 240 connects modulated data from a modulator 262 and demodulated data from a demodulator 264 to telephone line circuits such as a hybrid 270.

The dial tone detector of the detection circuit 250 detects a telephone line connection by sensing at least one of a loop current of at least about 20 milliamperes and a line voltage of about 7 volts. According to telephone standards, the telephone company must guarantee a loop current of at least 20 milliamperes and a line voltage of 7 volts for a telephone line.

When at least one or both of these characteristics are present, the dial tone detector of the detection circuit 250 determines that the telephone jack connector 210 is connected to a telephone line and not connected to a radiotelephone. The detection circuit 250 then provides a switch control signal to the control switch 240 to disconnect the modulated and demodulated data from isolators circuits 272 and 274 for the radiotelephone and to connect the modulated and demodulated signals to a hybrid circuit 270. The hybrid circuit 270 transforms the four-line, halfduplex outputs of the modulator 262 and demodulator 264 to provide a two-wire, full-duplex output for connection to the tip and ring lines of a telephone line. The hybrid 270 is a known circuit in the telephone art and can be implemented using discrete components or known integrated circuit implementation techniques.

FIG. 3 illustrates alternative preferred embodiments of the data modem having an interface according to the present invention. A radiotelephone detector 451 is used to control the control switch 240. The control switch 240, when connected to a radiotelephone detector circuit 250 in the embodiment of FIG. 2, would normally be in the telephone line mode. When the radiotelephone detector 451 in the embodiments of FIG.

3 detects control signals from a radiotelephone, then control switch 240 switches to a radiotelephone connection via isolators 272 and 274. The zener diodes 232,234 and 238 can alternatively be replaced by a relay 432.

The relay 432 can be controlled, for example, by a radiotelephone detector of a detection circuit 451 as also illustrated in FIG. 3. The radiotelephone detector 451 may built as part of the computer 220, or separate from the computer 220 as a custom integrated circuit. The radiotelephone connector 451 detects a radiotelephone control bus signal by looking for serial data communications received at the telephone jack connector 210 when the telephone jack connector is connected to a radiotelephone.

In an additional alternative embodiment, both a dial tone detector 455 and a radiotelephone detector 451 can be used as a detection circuit. In this alternative embodiment, control switch 240 is controlled via logic 457 by both the radiotelephone detector 451 and the dial tone detector 455. The control switch 240 thus connects to the isolators 272 and 274 when a radiotelephone is detected by the radiotelephone detector 451 and connects to the hybrid 270 when a dial tone is detected by the dial tone detector 455.

In this embodiment, extra security can be provided because the switch 240 would connect only when either a radiotelephone or a telephone line is positively identified by a detector circuit. The control switch does not need to default to a position when both the radiotelephone detector 451 and a dial tone detector 455 are used. If neither a radiotelephone nor telephone line is detected, the control switch 240 would be connected to neither the isolators 272 and 274, nor the hybrid 270.

The present invention thus allows elimination of a second connector for connection of the data modem to either a telephone line or a radiotelephone. By using the same connector for both connection to a telephone line or a radiotelephone, less space is consumed at the port of a computer, and a user is spared the burden of determining which connection jack to use for the data modem. Modems can now be built without the requirement of the addition of a connector dedicated for a radiotelephone connection.

Although the invention has been described and illustrated in the above description and drawings, it is understood that this description is by example only and that numerous changes and modifications can be made by those skilled in the art without departing from the true spirit and scope of the invention. For example, the interface of the invention can interface to other types of radios besides radiotelephones, such as trunked radios.

Furthermore, the invention should not be limited to interface data signals from data processing devices because voice signals may be used as the data signals.

Claims (10)

What is claimed is:

1. An interface between a data processing apparatus and a telephone line or a radiotelephone, said interface comprising: a joint connector capable of connection to either the telephone line or the radiotelephone; and a detector operatively coupled to said joint connector to sense characteristics of signals received at the joint connector to determine whether said joint connector is coupled to the telephone line or the radiotelephone.

2. An interface according to claim 1, further comprising a control switch operatively coupled to said telephone jack connector and said detector to switch connections to at least one pin of said joint connector in response to the determination by said detector.

3. An interface according to claim 2, further comprising a hybrid circuit operatively coupled to said joint connector and said control switch to selectively transform a duplex operation of signals received at the joint connector in response to the determination by said detector.

4. An interface according to claim 1, wherein said joint connector consists of a standard telephone jack connector and associated hardware.

5. An interface according to claim 5, wherein said standard telephone jack connector is a connector selected from the group consisting of RJ11 and RJ45 connectors.

6. An interface according to claim 5, wherein said joint connector consists of an RJ11 connector and associated hardware.

7. An interface according to claim 1, wherein said detector comprises a telephone line detector operatively coupled to said joint connector to detect a telephone line signal received at the joint connector when said joint connector is coupled to the telephone line.

8. An interface according to claim 8, wherein said telephone line detector comprises a circuit operatively coupled to said joint connector and capable of detecting at least one of a loop current of at least about 20 milliamperes and a line voltage of about 7 volts.

9. An interface according to claim 1, wherein said detector comprises a radiotelephone bus detector operatively coupled to said joint connector to detect radiotelephone bus signals received at the joint connector when said joint connector is coupled to the radiotelephone.

10. A method of interfacing between a data processing apparatus and a telephone line or a radiotelephone, said method comprising the steps of: (a) sensing characteristics of signals received at a joint connector; and (b) determining whether said joint connector is coupled to the telephone line or the radiotelephone based on the characteristics sensed in said step (a).