Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR SELECTIVE CONNECTION TO
TELEPHONE LINE OR RADIOTELEPHONE
BackQround of the Invention
0 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 full-
duplex 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
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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
0 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.
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Summary of the Invention
In accordance with one aspect of the present invention, there is
provided an interface between a data processing apparatus and a telephone
line or a radiotelephone. The interface comprises a joint connector and a
detector. The joint connector is capable of connection to either the
telephone line or the radiotelephone. The detector is operatively coupled
to the joint connector to sense characteristics of signals received at the
joint connector to determine whether the joint connector is coupled to the
telephone line or the radiotelephone.
In accordance with another aspect of the present invention, there is
provided a method of interfacing between a data processing apparatus and
a telephone line or a radiotelephone. The method comprising the steps of
(a) sensing characteristics of signals received at a joint connector; and
(b) determining whether the joint connector is coupled to the telephone
line or the radiotelephone based on the characteristics sensed in the step
(a).
Brief Des~ ,lion of the D~wi~
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.
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Detailed Description of the Plefelled Embodiments
Selective connection between a land telephone line and a radio
telephone is provided via a single standard telephone jack such as an RJ-
11 jack or other standard connector used by a given land telephone system.
0 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
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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
0 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 ~rereldbly 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
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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
0 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 prefeLably 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, half-
duplex outputs of the modulator 262 and demodulator 264 to provide a
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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
0 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 commur~ications 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
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5 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
o 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
- 15 of the invention. For example, the interface of the invention can interfaceto 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
slgnals.
