Cordless modem system having multiple base and remote stations which are interusable and secure

RELATED CASES

This is a continuation of application Ser. No. 08/541,287 filed on Oct. 10, 1995, now abandoned which is a continuation of application Ser. No. 08/242,122 filed on May 13, 1994. now abandoned

This application is related to Ser. No. 08/242,302, entitled “CORDLESS MODEM SYSTEM HAVING BASE AND REMOTE STATIONS WHICH IS COMMUNICATIONS SOFTWARE TRANSPARENT,” filed concurrently herewith.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a system having a cordless connection between a modem in a computer and a telephone land line, and more particularly to allowing multiple units and yet maintaining security of each connection.

2. Description of the Related Art

Mobile computers, particularly laptop computers and notebook computers have become increasingly popular. They have performance and capabilities near that of a desktop unit, and if color active matrix liquid crystal displays are utilized, the display is as good as a desktop unit. When combined with the mobility, the popularity is quite understandable. However, one problem with using portable computers is that often they need to be connected to various equipment. For example, when located in a office, it is desirable to connect to various office wide items or non-portable items. For example, a network interface is often necessary, as is a SCSI port for use with various external devices such as CD-ROMs. This situation has conventionally been handled using expansion bases, which contain expansion cards for network and SCSI use and connections for a video monitor, a printer and a full size keyboard, or port replicator strips, which are used to simply provide the connections to the monitor, printer and keyboard without the need for expansion cards.

One of the computer applications which is becoming prevalent is electronic mail or E-mail. The modern business often has a local area network (LAN), with E-mail and appointment calendar applications. A remote user, such as the laptop user away from the office needs to check periodically to maintain in full contact. Thus, a very common addition to a portable computer is a modem to allow remote access to the LAN or other dial up services. Typically this modem is installed in the laptop computer, not directly in any expansion base. So while an expansion base or port replicator may alleviate certain wiring problems, as the various cables need not be disconnected or connected when removing or installing the portable computer, it does not resolve the wiring concerns in the case of a modem, where a separate telephone line is still required to be plugged and unplugged into the modem in the computer. This results in aggravation for the user. Further, this phone line is yet another of the tangled mass of cables utilized with the modern computer. While the monitor, keyboard and SCSI cables are generally located right next to the computer to interconnect the various components, the telephone line often has to be strung across an office and thus is either unsightly or very difficult to route. This is a further drawback to standard conventional modem communications where the modem is contained in the personal computer, be it a laptop or a desktop unit.

Thus the use of a modem in a laptop computer results in aggravations for the user and additionally requires unsightly and cumbersome cabling. Therefore it is clearly desirable to simplify both the laptop portability concerns and the unsightly wiring problem.

SUMMARY OF THE PRESENT INVENTION

The present invention relates to a cordless modem system where a mobile station unit (MSU) is located in the computer or connected to the computer and a base station unit (BSU) which is connected to the telephone line. A radio frequency (RF) link is developed between the two units to allow a cordless connection between the computer and the telephone line. The BSU is completely powered from the telephone line, while the MSU is powered from the computer system. A software protocol is utilized between the two units to open a channel when a call is received or the computer wishes to go off hook. Each MSU and BSU have a personalized identification. The BSU is allowed to perform communications only with authorized and identified MSUs, while the MSU can perform communications only with BSUs with which it has previously communicated. A series of commands are present between the two units to allow the MSU to request a channel, the BSU to grant a channel, the BSU to notify of a ring, and the MSU to request the BSU to go off hook. In addition, there is preferably a command sequence to allow authorization of a particular MSU for use with the BSU.

Preferably, there are two channels in each MSU and BSU, each channel being full duplex. This presence of two channels allows multiple BSUs and MSUs to be utilized in a small area if desired. Once a particular BSU is receiving input or has made a connection with a particular MSU, the BSU is then dedicated to that MSU for the duration of the call. By having two channels, two BSUs can be present in the same environment. Communications between the two units are secure in that the BSUs and MSUs include collision detection logic to determine if both channels are already active. If so, the MSUs and BSUs do not start communication. If a channel is available, an MSU requests that channel, with the request command including the address or identification number of the MSU. The BSU receives the authorization request, checks its list of authorized MSUs and if present and the channel is available, provides a grant command to the MSU. When the BSU receives a call and a ring from the telephone line, after checking for an open channel, the BSU transmits a designated MSU identification along with a ring indication command so that only the specified MSU will answer the call. Further, the grant and ring indication commands include the BSU identification number so that the MSU will communicate only with that particular BSU while the call is on-going. In this manner, one MSU will not intercept the calls for another MSU after the link has been established and a BSU will not provide calls to unauthorized MSUS. This allows data transfer to be secure even though multiple MSUs are present and can generally share a single BSU.

Further, the development of the protocol is such that the communications software utilized in the computer is not even aware of the presence of the cordless connection. Both the MSUs and BSUs contain microcomputers and proper signaling to sense what action is requested from the modem or telephone line and perform the cordless or radio transmission function seamlessly. Thus conventional communication software can be utilized without any particular special commands or structure. This allows the user to continue to use his preferred communication software package.

Two embodiments of the MSU are provided, one configured as an external data access arrangement (DAA) to be connected with laptop modems configured to utilize external DAAs, while in the second embodiment the MSU is incorporated with the modem hardware to provide a single, fully integrated unit. The BSU is a single, preferably relatively small, box which simply plugs into the telephone line.

Thus by having this transparent cordless link, the laptop user does not have to disconnect or connect a telephone line each time he moves his laptop and further the telephone line need not be routed across open areas or through difficult passages.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings, in which:

FIG. 1

is a block diagram showing the computer, cordless connection and telephone jack according to the present invention;

FIG. 2

is a block diagram illustrating multiple computer and MSUs and multiple BSUs of

FIG. 1

;

FIG. 3

illustrates the frequencies used by the RF link;

FIG. 4

is a block diagram of the mobile station unit of

FIG. 1

;

FIG. 5

is a block diagram of the base station unit of

FIG. 1

;

FIG. 6

is a block diagram of a prior art modem utilizing an external DAA;

FIGS. 7A and 7B

are schematic diagram of the external DAA interface of

FIG. 6

;

FIG. 8

is the schematic diagram of the internal DAA of

FIG. 6

;

FIG. 9

is a block diagram of a combined modem and MSU unit according to the present invention;

FIG. 9A

is a diagram illustrating the installation of the integrated modem and MSU in a computer;

FIGS. 10A

,

10

B,

10

C,

10

D and

10

E are flowchart illustrations of the operation of the mobile station unit of

FIG. 1

; and

FIGS. 11A

,

11

B,

11

C,

11

D and

11

E are flowchart illustrations of the operations of the base station unit of FIG.

1

.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to

FIG. 1

, the basic arrangement of the components according to the present invention is shown. A computer system C, preferably a laptop or notebook computer but optionally a desktop computer, contains an internal modem M which is connected to a mobile station unit (MSU)

1

. The MSU

1

includes an antenna

400

. A telephone wall jack J is connected to telephone land line. A base station unit (BSU)

2

is connected to the telephone jack J and also includes an antenna

402

. A radio frequency (RF) link is established between the MSU

1

and the BSU

2

to pass information between the computer C and the telephone jack J. The MSU

1

contains a serialized identification number, preferably

24

bits long, as does the BSU

2

. This allows the MSU

1

to have a unique identity to allow security of communications. Similarly, the BSU

2

also has this identification to allow a secure link to be established. The MSU

1

is connected to the internal modem M by several alternate connections. In a first embodiment the MSU

1

is configured as an external data access arrangement (DAA) and is connected to an external DAA port of the internal modem M. In this embodiment the MSU

1

is contained in a small box or case. In an alternate embodiment the MSU

1

and the internal modem M are combined into a single unit, preferably in a PCMCIA form factor. The BSU

2

is connected only to the telephone jack J and is not otherwise powered but receives power from the telephone line. The BSU

2

is contained in a small box or case. The details of the MSU

1

and the BSU

2

are provided below.

The RF link between the MSU

1

and the BSU

2

is a two channel, full duplex link as illustrated in FIG.

3

. Center frequencies of 35.2 MHz and 43.24 MHz are preferably utilized with each channel. Each channel is developed as a five kHz sideband of the basic carrier, so that each channel has a 10 kHz bandwidth. The 35.2 MHz frequency is used as the transmit channel from the BSU

2

to the MSU

1

, while the 43.24 MHz frequency is used as being receive channel from the MSU

1

to the BSU

2

. The separation of frequencies allows both for duplex operation and also means that the MSU's

1

are not capable of receiving signals being transmitted by other MSU's, so that security is enhanced. The security process is described in more detail below.

Referring now to

FIG. 2

, a more complex arrangement is shown. In this case three computers C

1

, C

2

and C

3

include respectively MSUs

1

,

1

′ and

1

″. In addition, there are two telephone jacks J

1

and J

2

receiving respectively BSU

2

and BSU

2

′. The two BSU

2

and BSU

2

′ are within the signal range of each other, so that if they were to utilize the same channel interference would occur. However, because two different channels are utilized, two BSUs can communicate within the same general area. Each MSU

1

, MSU

1

′ and MSU

1

″ is free to communicate with either BSU

2

or BSU

2

′ depending upon channel availability and authorization access of the particular BSU

2

and BSU

2

′.

Referring now to

FIG. 4

, the block diagram of the MSU

1

is shown. An RJ 45 connector

404

is provided in the MSU

1

to allow connection of a cable between the MSU and the internal model M. A modem interface

406

is connected to the RJ 45 connector

404

and interfaces with the various signals. A power supply

408

is provided and connected to the modem interface

406

to receive power from the computer C and to provide the proper voltages for operation of the MSU

1

. DAA identifier logic

410

is connected to the modem interface

406

to identify that the MSU

1

is connected to the internal modem M. A microcontroller

412

, preferably the 68HC05 from Motorola, operates as the control point for the MSU

1

. A dual tone multi frequency (DTMF) decoder/encoder

414

is provided to allow signaling and dialing if necessary. An RF transmitter

416

is connected to properly frequency modulate the received audio signal and provide it to an antenna

418

. The transmitter

416

is controlled by the microcontroller

412

. A receiver

420

is connected to the microcontroller

412

and the antenna

418

to receive the RF signal from the base station BSU

2

and provide the audio signal to the modem interface

406

. The receiver

420

is similarly controlled by the microcontroller

412

.

Now the connections between the blocks will be described in more detail. The modem interface

406

receives the MODEM_CLK signal from the RJ 45 connector

404

and inverts and buffers this signal to develop a ˜MODEM_CLK signal provided to the DAA identifier logic

410

. In this description a tilde prefix or an asterisk suffix is used to indicate a negative logic signal which is active when asserted low. The signal name without the tilde or asterisk means that it is the inverse of that signal with the tilde or asterisk. Similarly, the modem interface

406

receives the ˜DTAL or inverted data signal from the DAA identifier circuitry

410

and provides a buffered and inverted version to the RJ 45 connector

404

. The DAA identifier logic

410

is configured to provide a code to the internal modem M to indicate the presence of the MSU

1

should the internal modem M need to make any changes. Conventionally the DAA identifier logic

410

provides the country code of the particular country for which the mobile station MSU

1

and base station BSU

2

are configured for operation. In an alternate embodiment the MODEM_CLK signal could be provided to the microcontroller

412

, which would then provide the DTAL signal. This embodiment slightly complicates the programming but also reduces the cost and space by allowing removal of the separate DAA identifier logic

410

.

An RIL* or inverted ring indication signal is provided from the modem interface

406

to the RJ 45 connector

404

, which in this case is simply a buffered version of the to be ˜RING_IND or ring indication signal provided by the microcontroller

412

. The OH* or inverted off hook signal from the RJ 45 connector

404

is inverted and provided to the microcontroller

412

to indicate that the internal modem M has requested the telephone line to go off hook. The TXA and RXAC or transmit analog and receive analog signals from the RJ 45 connector are provided to the modem interface

406

. The TXA signal is combined with signals referred to as FSK_TX and DTMF_TX or frequency shift keyed and DTMF transmit signals by an operational amplifier circuit to develop the AUDIO_TX signal which is provided to the transmitter

416

. Preferably the mobile station MSU

1

can provide either the analog or audio data being received from the internal modem M, which is utilized for conventional data communications, or can provide an FSK signal, which is utilized for command operations with the BSU

2

. The FSK_TX signal is a buffered signal provided from a serial output of the microcontroller

412

. Preferably DTMF tones can also be provided when necessary. An ˜AUDIO_EN or audio enable signal from the microcontroller

412

is associated with the AUDIO_TX signal in that it clamps the TXA signal being provided to a low level so that the FSK_TX signal used in the command phase is unimpaired. An AUDIO_RX signal received from the receiver

420

, which is the audio or analog data received over the RF link, is provided in a buffered format to the RXAC output. The ˜AUDIO_EN signal also acts to clamp the AUDIO_RX signal to a low level. Additionally, the RJ 45 connector

404

provides ground and 5 volt connections to the modem interface

406

. The modem interface

406

passes the 5 volt and ground connections to the power supply

408

.

The power supply

408

provides a 3 volt output for operation of the circuitry of the preferred embodiment, to save power, and provides VCC_TX and VCC_RX signals which provide power to the transmitter

416

and the receiver

420

so that they can be completely powered down when not in operation. To the end, the VCC_TX_EN and VCC_RX_EN signals are received from the microcontroller

412

to control or enable the VCC_TX and VCC_RX outputs. The power supply

408

also provides the ˜RESET signal to the microcontroller

412

to reset the operation of the MSU

1

when the power supply is inadequate.

The DTMF decoder/encoder

414

provides the DTMF_TX output, which is used if dial tones are desired, and receives the AUDIO_RX signal from the receiver

420

to allow decoding of any received DTMF signals. The DTMF decoder/encoder

414

is connected to the microcontroller

412

through data and control signals so that the decoder/encoder

414

can interrupt the microcontroller when a detected DTMF code is received and can provide a bi-directional data and control port.

The transmitter

416

includes a radio frequency phased-locked loop (PLL) synthesizer (not shown) which includes a serial interface. The PLL receives command and setup data from a serial data link comprised of the signals MOSI, MISO and SCK from the microcontroller

412

. The SCK signal is the clock signal while the other two signals are for the data input and data output. The serial interface allows the microcontroller

412

to properly program the PLL contained in the transmitter

416

to the desired frequency of channel

1

or channel

2

. The output of the PLL is then provided to appropriate mixing circuitry to mix in the AUDIO_TX signal to produce the RF_TX signal, which is provided to the antenna

418

. The antenna

418

can either be an integrated antenna or a short external antenna. Additionally, the microcontroller

412

provides the TX_RF_EN and TX_PLL_EN signals to the transmitter

416

. The TX_PLL_EN signal is used to enable or disable the PLL when desired, while the TX_RF_EN signal disables the actual output of the transmitter

416

which is provided to the antenna

418

. This allows the PLL to be activated or turned on in preparation for a transmission which is to occur.

Similarly, the receiver

420

includes a similar PLL, preferably the MC145170 from Motorola Semiconductor. The receiver

420

includes the MOSI, MISO and SCK signals. The transmitter

416

receives the VCC_RX signal from the power supply

408

to allow it to be completely powered down. An RX_PLL_EN signal is provided from the microcontroller

412

to receiver

420

to disable the PLL in the receiver

420

. The receiver

420

also includes a mixer FM IF system, preferably the NE/SA606 from Phillips Semiconductor. The mixer FM IF system receives an RF_RX signal from the antenna

418

and properly mixes out the channel receive frequency so that only the received audio data is present. This is provided as the AUDIO_RX signal to the DTMF decoder/encoder

414

and the modem interface

406

. An FSK_RX signal is a buffered version of the AUDIO_RX signal and is provided to a serial input of the microcontroller

412

. Thus the FSK_TX and FSK_RX signals are serial output and input of the microcontroller

412

. This serial interface of the microcontroller

412

is the command interface with the BSU

2

. Preferably the serial interface operates at a low speed, such as 1200 or 2400 baud. The receiver

420

also provides an RSSI or receive signal strength indication to the microcontroller

412

to indicate that the carrier is being received from a BSU

2

and that a channel is active. This allows the MSU

1

to monitor for a received signal indicating that a given channel is busy.

Thus the MSU

1

provides the capability to receive analog audio data from the computer C and provide it over an FM modulated RF link to the base station BSU

2

and to similarly receive an RF signal from the base station BSU

2

and decode the signal to provide the RXAC analog signal to the computer C. The microcontroller

412

provides the control function which is needed for the modem interface and allows command passing between the base station BSU

2

and MSU

1

.

Referring now to

FIG. 5

, a block diagram of the BSU

2

is shown. As can be seen, the organization is very similar to that of the mobile station MSU

1

except that the modem interface

406

has been replaced by a DAA

422

. An RJ11 connector

424

is provided to connect the data access arrangement (DAA)

422

to the phone line. The DAA

422

is connected to a transmitter

426

, a receiver

428

, a microcontroller

430

, a DTMF decoder/encoder

432

and a power supply

434

. The DTMF decoder/encoder

432

, the transmitter

426

and the receiver

428

are configured in the fashion similar to that of the mobile station MSU

1

and will not be further described in detail. Again, the microcontroller

430

is similar, preferably an M68HC05. The DAA

422

contains the necessary interface between the telephone line TIP and RING signals which it receives as inputs and the various other signals in the base station BSU

2

. The TIP and RING signals are provided to the power supply

434

to allow the base station BSU

2

to be entirely powered by the telephone line. For more details on this technique, please refer to copending application Ser. No. 08/242,314, filed concurrently herewith and titled “TELEPHONE LINE SOURCED POWER SUPPLY,” which is hereby incorporated by reference. The power supply

434

provides the desired

3

volt signal and transmitter and receiver voltages as necessary. The DAA

422

includes a two wire to four wire conversion to develop the RX signal and utilize the TX signal as is conventionally known. Details of this conversion are not included but an example is illustrated in U.S. Pat. No. 5,127,046, which is hereby incorporated by reference. Similarly, in the DAA

422

, the FSK_TX and DTMF_TX signals are utilized and combined with the audio signal received from two to four wire converter to provide the AUDIO_TX signal. The ˜AUDIO_EN signal is used to clamp or disable the audio signal from the two to four wire converter and AUDIO_RX signals so that the microcontroller

430

can properly communicate with the MSU

1

. A RING_IND signal provided from the DAA

422

to the microcontroller

430

provides a ring detection indication which can be transmitted via a command to the MSU

1

. The ˜OFF_HOOK signal is provided from the power supply

434

to the DAA

422

and is a combination of a VCC_TX_EN signal and a signal indicating that the power supply

434

needs recharged. Basically the power supply

434

includes a very large capacitor which is utilized to power the BSU

2

and the capacitor needs periodic recharging from the DC voltage present on the telephone line. When recharging is necessary, the power supply

434

causes the BSU

2

to momentarily go off hook to charge the capacitor. Thus, the ˜OFF_HOOK signal is developed either by the power supply

434

for charging or by the microcontroller

430

when communications are desired based on the VCC_TX_EN signal. In other respects the operation and configuration of the BSU

2

is the same as the mobile station MSU

1

and details are not provided.

Referring now to

FIGS. 6

,

7

A,

7

B and

8

, these are block diagrams and schematics of a prior art modem which is located internal to a laptop computer and includes provisions for an external DAA. This modem is used in the preferred embodiment as the MSU

1

of

FIG. 4

is designed to work with the external DAA connection. The modem

12

of

FIG. 6

has a preference to use a device connected to the external DAA connection prior to using the internal DAA, so that if the MSU

1

is present, it will be utilized rather than the landline interface present on the modem

12

. This description is provided for full enablement and to allow better understanding of the connections and operation of the mobile station unit MSU

1

.

FIG. 6

shows a logical block diagram of the various elements of the modem

12

. The modem

12

preferably consists of two circuit boards combined to form the small unit which can be contained in a laptop computer. A motherboard MO contains all of the components, including an RJ11 type jack

14

and an RJ45 type jack

16

, except those forming the internal DAA. The components of the internal DAA are located on a daughterboard DA which overlies the motherboard MO. This allows easy substitution of internal DAA's for various countries without requiring complete design of the entire modem

12

, particularly the motherboard MO. The laptop computer physically contains the modem

12

and connects via an internal connector to a UART/support chip

100

. The UART/support chip

100

typically connects to the host bus of the laptop computer, for example an EISA or ISA bus or PCMCIA interface, although it could be any type of typical communications bus. The UART/support chip

100

then appears as a universal asynchronous receiver transmitter (UART) to the laptop computer. The UART/support chip

100

connects to, among other things, a microcontroller

102

by both serial and parallel buses. The UART/support chip

100

provides a variety of functions to the modem

12

, including communications to the laptop computer, clock controls, configurable registers, and power down control for the microcontroller

102

. The UART/support chip

100

is typically an application specific integrated circuit, but could instead be constructed of discrete components.

The microcontroller

102

is typically an embedded controller, and in the preferred embodiment is a 68302 integrated multiprotocol processor, manufactured by Motorola Incorporated. A read only memory (ROM)

101

and random access memory (RAM) and non-volatile RAM (NVRAM)

103

are provided to allow for sufficient ROM and RAM space to contain the necessary firmware and data to operate the modem

12

.

The microcontroller

102

communicates with a data pump

104

by both serial and parallel buses. The data pump

104

is typically a modem data pump chip set supporting the various protocols of modem communication, including V.32bis protocol and fax protocols. In the preferred embodiment, the data pump

104

is a WE® DSP16A-V32FB-LT V.32bis plus FAX Data Pump Chip Set, sold by AT&T Microelectronics, and configured for 14.4 Kbps operation as a fax/modem. This chip set includes a digital signal processor (DSP) support chip

106

, a DSP

108

, and a coder-decoder (CODEC)

110

. This chip set is interconnected according to AT&T specifications and provides the typical data pump features of control, analog-digital and digital-analog conversion, digital signal processing, and interfacing.

The microcontroller

102

communicates with the data pump

104

by both serial and parallel buses. The serial bus is used to transmit and receive data that will become the transmitted and received modem data, while the parallel bus is used to control and configure various features within the data pump

104

. These features are controlled through the DSP support chip

106

. The data pump

104

converts the digital serial data provided by the microcontroller

102

into the appropriate analog format. This is typically done by the DSP

108

, which then transmits and receives the data via the CODEC

110

.

The CODEC

112

connects to the actual external lines through analog transmit and receive signals, TXA and RXAC. These signals are selectively connected to either an internal DAA

112

or a cellular/external DAA interface

114

. Details are provided below. The internal DAA is then connected to a telephone line by the RJ11 type jack

14

, while the cellular/external DAA interface

114

can be connected through the RJ45 type jack

16

to an external DAA, a cellular phone or to the MSU

1

.

Various signals are typically used to interface with telephone lines, including the ring indicator signal RI* and the off hook control signal OH*. A DAA generates and receives these signals, as well as the TXA and RXA signals, and converts them into a format suitable for that particular country's two-wire telephone system, or whatever type of telephone system to which the DAA is connected. The internal DAA

112

and the cellular/external DAA interface

114

receive OH* from the DSP support chip

106

. Three lines are bi-directionally connected to the cellular/external DAA interface

114

and to the internal DAA

112

. They are the lines carrying the RI* signal, a data signal DTA, and a clock signal CLK*. The functions of these signals in the modem

12

will become apparent.

The microcontroller

102

determines what is externally connected to the jacks and selects whether to use the cellular/external DAA interface

114

or the internal DAA

112

. The microcontroller

102

further selects whether to use the cellular/external DAA interface

114

in a cellular phone mode or an external DAA mode. This is all done via the RI* signal, the DTA signal, and the CLK* signal, and the circuitry to accomplish this will be shown and described later.

The microcontroller

102

uses the parallel bus between it and the UART/support chip

100

to configure and determine the status of the UART/support chip

100

. The UART/support chip

100

includes a number of registers addressable by the microcontroller

102

. The registers provide for control of and access to a number of digital input/output (I/O) pins on the UART/support chip

100

. One register provides the direction of each pin, either input or output. Another register provides the data value of bits which are set as outputs during a write operation and all data values when read. Additional bits can select the output pins as being tri-stated. Yet another register can select the various pins as causing an input to the microcontroller

102

upon a transition.

The laptop computer sends and receives data to the modem

12

via the UART/support chip

100

, which then serially communicates that data to the microcontroller

102

. The microcontroller

102

then establishes a communications link through either the internal DAA

112

or the cellular/external DAA interface

114

, whichever is selected. To establish the communications link, the microcontroller

102

directs the proper sequence of signals to either originate or answer a telephone call. For example, in the land line model, the microcontroller

102

typically directs the DSP support chip

106

to drive the OH* signal low, then, after configuring the data pump

104

through their parallel bus, “listens” for a dial tone on the line, and then directs the data pump

104

to dial the number. Then, the microcontroller “listens” for an answer carrier through the data pump

104

, and then directs the data pump

104

to establish whatever type of data communications link is desired. For the cellular phone

22

, the sequence will be cellular specific, but the principles of establishing a data communications link are the same.

After establishing a data communications link, the microcontroller

102

serially sends to the data pump

104

the data to be transmitted to the communications device. The data pump

104

then processes this serial digital data and converts into an analog form suitable for communication at the rate and in the protocol desired. It then transmits this information via the TXA signal to the device the microcontroller

102

has selected, the cellular/external DAA interface

114

or the internal DAA

112

, which then communicates via the active jack. Similarly, received data is transmitted from the active jack through the cellular/external DAA interface

114

or the internal DAA

112

to the data pump

104

, which subsequently transmits that data to the microcontroller

102

, which then transmits the data to the laptop computer by way of the UART/support chip

100

. Of course, the microcontroller

102

may perform compression/decompression functions on the data going either direction, or otherwise “massage” the data.

FIGS. 7A and 7B

show the circuitry for selecting between utilizing the RJ

45

type jack

16

and the RJ11 type jack

14

. This selection circuitry selects between the RJ45 type jack

16

shown in

FIGS. 7A and 7B

, and an internal DAA connector

200

, which then connects to the RJ11 type jack

14

via the internal DAA

112

, as will be shown later in FIG.

8

. This selection is accomplished by an internal selection signal INTERNAL, which is provided by the microcontroller

102

. The inverse of this signal, INTERNAL*, is generated by a MOSFET

202

in an inverting configuration. In the preferred embodiment, the MOSFET

202

is a 2N7002. When INTERNAL is true, the internal DAA connector

200

is active. When INTERNAL is false, then INTERNAL* is true, and the RJ45 type jack

16

is selected for communications.

This selection process is accomplished by activation and deactivation of CMOS switches, preferably provided in CD4016 devices. Specifically, when INTERNAL is low, INTERNAL* is high, and the RJ45 type jack

16

is connected by CMOS switches to the various signal lines required for communications with the data pump

104

, the UART/support chip

100

, and the microcontroller

102

and the internal DAA connector

200

has connections removed from those signal lines by other CMOS switches. The TXA signal is connected to the RJ45 type jack

16

TXAL signal line via a switch

204

. Similarly, the RXA signal is connected to the RJ45 type jack

16

RXAL signal line via a switch

206

, the RI* signal is connected to the RJ45 type jack

16

RIL* signal line via a switch

208

, and the DTA signal is connected to the RJ45 type jack

16

DTAL signal line via a switch

210

. Note that a separate data signal DTAI is also provided for connection to the signal line DTAL. This is for separate control by the microcontroller

102

, and is simply provided in the preferred embodiment to allow for independent control by the microcontroller

102

of the RJ45 type jack

16

DTAL line when the switch

210

is turned off.

When INTERNAL goes high, the internal DAA connector

200

becomes active. The TXA line is then connected to the internal DAA connector

200

TXA

0

signal line via a switch

212

, the RXA line is connected to the RXA

0

signal line via a switch

214

, the RI* signal is connected to the RI

0

* signal line via a switch

216

, and the DTA signal is connected to the DTA

0

signal line via a switch

218

.

The CLK* signal remains connected to both the RJ45 type jack

16

and the internal DAA connector

200

at all times. The CLK* signal can be used bi-directionally by both the microcontroller

102

and the UART/support chip

100

. It is typically, however, used as an input when using a Motorola or Nokia cellular phone, or when using the internal DAA

112

and it is on hook. CLK* is typically used as an output when using either DAA and they are off hook, or when using the external DAA

24

and it is on hook. The OH* signal is provided to the RJ45 type jack

16

as the OH*L signal line.

Also connected to the RJ45 type jack

16

are the ground signal GNDL and the 5 volt power supply +5VL. All of the signals on the RJ45 type jack

16

are protected and isolated by clamping diodes or transorbs

220

and inductors

222

. The 5 volt power supply +5VL is selectively provided to the RJ45 type jack

16

when the signal DAAPWR* goes true, or low. When DAAPWR* goes low, it turns on RJ45 type jack power supply enable circuitry

224

, which then drives +5V to the RJ45 type jack

16

+5VL line via the inductor

222

.

Before connecting to the RJ45 type jack

16

or the internal DAA connector

200

, the TXA signal is filtered and driven. Specifically, the TXA signal is coupled through a capacitor

226

, a resistor

228

, and another resistor

230

. A gain reduction block can be added if desired. It is then driven into a low pass filter

232

, whose cutoff frequency is well above the highest frequency needed for modem communications. Here, that cutoff frequency is approximately 42 kHz. The signal is then transmitted through a resistor

234

, the switch

204

, and a coupling capacitor

236

. After the coupling capacitor

236

, the line can also be sensed or selectively pulled up or down via the signal LCS, connected via a resistor

238

. The signal LCS, as well as signals EARTH* and DAAPWR are connected to the digital I/O pins of the UART/support chip

100

to allow the microcontroller

102

to control or monitor these signals. The PB

1

, PB

10

, and INTPWR* signals are supplied by the microcontroller

102

. These signals are provided for compatibility with international and national standards, for implementation of protocols used by the modem

12

, and for control of the cellular phone. Further, PB

10

provides the microcontroller

102

with direct control of the RI* signal.

Similarly, the RXAL signal, before being transmitted to the data pump

104

, is received from the RJ45 type jack

16

, and driven through the inductor

222

and a coupling capacitor

240

. It is then selectively driven through the switch

206

, and is then provided to other circuitry in the modem

12

as the RXA signal. As the data pump

104

requires coupling of the RXA signal, the CODEC

110

of the data pump

104

is provided with an RXAC signal, which is generated by coupling the RXA signal in a coupler

242

.

When the internal DAA connector

200

is selected by the switches

212

and

214

, the TXA

0

signal is first filtered through a capacitor

244

before being driven externally. This capacitor

244

is connected to the switch

212

. The RXA

0

signal is also first filtered through a capacitor

246

before being driven through the switch

214

. The previously mentioned signal LCS, in addition to providing a sense and a selectable pull up/pull down to the TXAL signal, also senses or selectively pulls up or down the TXA

0

signal between the internal connector

200

and the capacitor

244

via a resistor

248

. The EARTH* signal also provides a sense or selectable pull up/pull down of the RXAL signal between the RJ45 type jack

16

and the capacitor

240

via a resistor

250

and provides a sense or selectable pull up/pull down of the RXA

0

signal between the internal DAA connector

200

and the capacitor

246

via a resistor

252

. The PB

10

signal provides a sense or selectable pull up or down of the RIL* line via a resistor

254

, and the PB

1

signal is used to selectively attenuate the TXA signal via a resistor

256

, a capacitor

258

, and a switch

259

, after that signal has been filtered through the capacitors

226

and

228

. The DTAL and CLKL signals are pulled up to 5 volts through, respectively, resistors

260

and

262

. On the internal DAA connector

200

, two additional signals are provided. These are the internal power select signal INTPWR*, which is also pulled up by a resistor

264

, and the REF signal, which is a 2.5 volt precision reference.

FIG. 8

shows circuitry associated with the internal DAA

112

and provides an example of the DAA identifier circuitry

410

in the MSU

1

. Three main blocks of circuitry are shown: the country or DAA identification circuitry

300

, the power down circuitry

302

, and the DAA circuitry

304

. This circuitry is typically all placed on one board that is then connected to the main board of the modem

12

by connectors

305

and

306

, which connect to the internal DAA connector

200

. This allows for convenient swapping of internal DAA's when one desires to move to or remain in a different country. As previously discussed, the RJll type jack

14

is typically located on the main board of the modem

12

, and the connector

305

allows lines from the DAA circuitry

304

to connect to the RJll type jack

14

. Typically, the connectors

305

and

306

are separate physical connectors.

The DAA circuitry

304

is typical DAA circuitry used to connect a modem to a land line, or physical telephone line, and uses the standard signals TIP, RING, TIPV, RINGV, and GRNDSTRT. The internal DAA

112

is connected to the internal DAA connector

200

via the connector

306

. All of the signals from the connector

306

connect to the DAA circuitry

304

. The signals INTPWR* and the +5V power line connect to the power down circuitry

302

. When INTPWR* goes low, the power down circuitry

302

is enabled, and power is supplied to the DAA circuitry

304

through the signal INTDAAPWR. Specifically, a power switch

307

is connected to the +5V signal and to the signal INTPWR*. INTPWR* going low turns the power switch

307

on, providing power to an inductor

309

that then provides power to the DAA circuitry

304

. Filtering the supplied power, and connected between the inductor

309

and ground, is a filtering capacitor

311

. The power down circuitry

302

is standard switching circuitry, and is well known to those in electronic design.

The country identification circuitry

300

includes a shift register

308

, which in the preferred embodiment is a 74HC165. The shift register

308

has certain of its parallel inputs pulled up by pullup resistors

310

and certain of its parallel inputs pulled down by pulldown resistors

312

to indicate a particular country. The output QH of the shift register

308

is driven to its serial input S

1

as well as to an output buffer

314

. The output buffer

314

is typically a 74HC126, and its output selectively drives the data line, DTAO. The LD*/SHF signal input of the shift register

308

is driven by an RC circuit consisting of a resistor

316

and a capacitor

318

. The resistor

316

is connected to the CLKL signal and to the capacitor

318

, which is then connected to ground. The LD*/SHF signal input of the shift register

308

is connected between the resistor

316

and the capacitor

318

. This signal is also connected to the enable line of the output buffer

314

.

When the LD*/SHF signal is high, the output buffer

314

is enabled, and the shift register

308

serially outputs the contents of its parallel inputs on its QH output as clocked by its CLK signal input, which is connected to CLKL.

The time constant of the RC filter made up of the resistor

316

and the capacitor

318

is approximately 0.5 milliseconds. When the clock is running at its slow rate, which has a period of much greater than 0.5 milliseconds, the LD*/SHF signal remains low, as does the enable line to the output buffer

314

. This instructs the shift register

308

to load its parallel inputs A through H as specified by the pull up resistors

310

and the pull down resistors

312

, and tristates the output buffer

314

. When the CLKL signal is sped up, the LD*/SHF signal goes high, enabling the buffer

314

and causing the shift register

300

to shift data on the rising edges of the CLKL signal.

The pull up resistors

310

and the pull down resistors

312

are connected in an arbitrary way to indicate which country's telephone lines the DAA circuitry

304

is constructed to communicate with. In

FIG. 8

, the A, B, C, and D lines of the shift register

308

are pulled up, and the E, F, G, and H lines are pulled down. When clocked out, they serially clock out as “00001111.” For another country, another arbitrary value is used. Further, all eight bits need not be used to designate country codes. For example, they can designate a type of DAA such as the MSU

1

, or a particular configuration.

In this way, the microcontroller

102

can determine the configuration of the internal DAA

112

by “twiddling” the CLK signal and then reading the DTAO signal returned, which is returned to the microcontroller

102

as the DTA signal. This circuitry is repeated on any attached external DAA

24

in a similar manner. In addition, all eight bits need not be used for country encoding but can also be used for other decoding purposes.

The microcontroller

102

, through its signal lines INTERNAL and signal lines INTPWR* and DAAPWR* can both select and power up and down both the internal DAA

112

and any external DAA

24

. The INTERNAL line allows for selection between the RJ45 type jack

16

and the internal connector

200

, while the INTPWR* and DAAPWR* signals respectively provide for powering up or down the internal DAA

112

or any external DAA

24

. The powering up and down of the internal versus the external DAA's is important on a laptop or notebook computer, as keeping these DAA's powered up requires a good deal of energy. Thus, by powering down these DAA's when they are not required, the laptop computer that uses the modem

12

can experience significantly increased battery life because of these power saving features of the modem

12

.

FIG. 9

shows the block diagram of an alternate arrangement where the MSU

1

is integrated with the internal modem M preferably on a single PCMCIA type II form factor card. In this embodiment the modem M′ does not include an RJ11 connector

14

but rather only includes a dual keyed RJ45 connector

16

which is connected to the external DAA interface

114

. It is noted that the cellular connection is preferably disabled though it could optionally be utilized. Preferably also no internal DAA

112

is present for space reasons, instead utilizing an external DAA to a land line for direct wired communications. The internal DAA