Modem unit

Abstract: A modem unit adapted to be coupled between a land or radio telephone line and terminal equipment. The modem unit comprises modem circuit means (8,27,85,507), coupled to the terminal equipment (250,251,506), for modulating data received from the terminal equipment and for demodulating data transmitted to the terminal equipment, and isolation means (C1,C2,34), coupled to the modem circuit means (8,27,85,507), for providing DC isolation between the telephone line and the terminal equipment (250,251,506), both the modem circuit means and isolation means being provided on the same modem integrated circuit card. The modem unit also includes a battery (515) for supplying power to various parts of the modem unit; detection means (502), coupled to the battery, for detecting an output voltage level of the battery; and selection means (504), coupled to the detection means, for selecting a frequency of a clock which drives the modem circuit means depending on the voltage level detected by the detection means. The modem circuit means (507) includes determination means (508), coupled to the detection means, for determining a modem function of the modem circuit means based on the voltage level detected by the detection means and function request information specified from the terminal equipment (506).

Description: BACKGROUND OF THE INVENTION The present invention generally relates to modem units, and more particularly to a modem unit which enables a data exchange between personal computers and the like via a telephone line. The size and thickness of portable personal computers, portable word processors and the like have been reduced by the recent technological development, and they continue to be further reduced. On the other hand, data communications between computers via telephone lines have also become popular. When making such data communications, a modem converts a digital signal into an analog signal and transmits the analog sigal to the telephone line, and also receives the analog signal from the telephone line and converts the analog signal into a digital signal. When using a modem in the form of a modem IC card with a portable data processing unit, for example, it is important that the power consumption of the modem IC card is small particularly when the modem IC card is battery-operated. In other words, it is desirable that the power consumption of the modem IC card is small so that the modem IC card can be used for a long time without the need to replace or charge the battery thereof. "Direct-coupled modem", Elektor, no. 10, October 1984, pages 48-55 discloses a modem unit according to the preamble of accompanying claim 1. SUMMARY OF THE INVENTION Accordingly, it is a general object of the present invention to provide a novel and useful modem unit in which the problems described above are eliminated. According to the present invention, there is provided a modem unit adapted to be coupled between a land or radio telephone line and terminal equipment, said modem unit comprising modem circuit means, coupled. to the terminal equipment, for modulating data received from the terminal equipment and for demodulating data transmitted to the terminal equipment, and isolation means, coupled to said modem circuit means, for providing DC isolation between the telephone line and the terminal equipment, said modem circuit means and said isolation means being respectively provided on a single modem integrated circuit card; characterised in that there are further provided: a battery for supplying power to various parts of the modem unit; detection means, coupled to said battery, for detecting an output voltage level of said battery; and selection means, coupled to said detection means, for selecting a frequency of a clock which drives said modem circuit means depending on the voltage level detected by said detection means, said modem circuit means including determination means, coupled to said detection means, for determining a modem function of said modem circuit means based on the voltage level detected by said detection means and function request information specified from the terminal equipment. According to the modem unit of the present invention, it is possible to automatically continue the data communication even if the voltage level of the battery fails, by reducing the clock frequency and reducing the modem functions. Other features and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system block diagram showing an example of a conventional modem unit; FIG. 2 is a system block diagram for explaining the operating principle of first and second embodiments of the modem unit according to the present invention; FIG. 3 is a system block diagram showing the first embodiment; FIG. 4 is a system block diagram showing an embodiment of a modem processor of the first embodiment; FIG. 5 is a system block diagram showing the second embodiment; and FIG. 6 is a system block diagram showing an embodiment of the modem processor of the second embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a description will be given of the problems of a conventional battery-operated modem unit, by referring to FIG. 1. In FIG. 1, a modem unit 480 is connected between the telephone line and a terminal equipment 481 such as a portable personal computer. The modem unit 480 modulates send data which is output from the terminal equipment 481 into an analog signal, and transmits the analog signal to a remote end via the telephone line. In addition, the modem unit 480 demodulates analog received data which is received from the remote end via the telephone line into digital data, and supplies the digital data to the terminal equipment 481. The modem unit 480 includes an oscillator 482, a power unit 483 which is a battery in this case, and a modem processor 484. The modem processor 484 is made up of a modem controller 485 and a modem circuit 486. The oscillator 482 generates clock pulses for driving the modem processor 484. The power unit 483 supplies the driving power to the modem processor 484. The modem processor 484 modulates the send data and demodulates the received data in response to the clock pulses generated from the oscillator 482. The modem controller 485 controls the input and output of the send data and the received data, and also controls the modulation and demodulation. The modem controller 485 includes a clock pulse input terminal CLK for receiving the clock pulses, a power source voltage input terminal Vcc for receiving the power source voltage, an input terminal SD for receiving the send data from the terminal equipment 481, and an output terminal RD for outputting the demodulated received data. The modem circuit 486 includes a modem and a processor. The modem modulates the send data in response to the clock pulses, and also demodulates the received data in response to the clock pulses. On the other hand, the processor carries out a predetermined processing on the data such as error correction, data compression and data expansion depending on the communication mode which is determined by the communication between the terminal equipment 481 and the terminal equipment (not shown) on the remote end. However, the frequency of the clock pulses generated from the oscillator 482 was conventionally fixed. Hence, it is possible to reduce the power consumption of the modem unit 480 by decreasing the frequency, but the processing speed of the modem unit 480 will deteriorate in this case. For this reason, the frequency of the clock pulses is set to a frequency which is as high as possible. It is conceivable to obtain the power for the modem unit 480 from the telephone line. However, the power which can be obtained from the telephone line is small, and an LSI which can operate at such a small power only has a communication speed of approximately 1200 bps at the maximum. But the recent modem unit generally operates at the communication speed of 2400 bps and require functions such as self-error correction, data compression/expansion, it is virtually impossible to satisfactorily drive such a modem unit by the power obtained from the telephone line. On the other hand, it is also conceivable to have the terminal equipment carry out the functions such as self-error correction and data compression/expansion, but this would only shorten the life of the battery which drives the terminal equipment. Next, a description will be given of the operating principle of first and second embodiments of the modem unit according to the present invention, by referring to FIG. 2. In these embodiments, the modem unit is normally driven by high-frequency clock pulses when the power source voltage of the modem unit is sufficiently high. But if the power source voltage decreases, the frequency of the clock pulses is decreased automatically so as to operate at a lower power consumption. It is also possible to simplify the processes by eliminating the error correction function, for example. The modem unit on the remote end is notified of the mode of the modem unit, so that the communication can be made according to the mode. In FIG. 2, a modem unit 501 has the form of the modem IC card and is loaded into a terminal equipment 506 which may be a portable personal computer. Of course, the modem unit 501 in principle may be connected externally to the terminal equipment 506. The modem unit 501 generally includes a battery 515, a power source voltage detection circuit 502, a voltage holding circuit 503, a clock generator 504, and a modem processor 507. The battery 515 may be built into the modem unit 501 or may be the power unit of the terminal equipment 506 in the case where the modem unit 501 is loaded into the terminal equipment 506. For the sake of convenience, it will be assumed that the battery 515 is built into the modem unit 501. The voltage detection circuit 502 detects the voltage state of the battery 515. The voltage holding circuit 503 holds a voltage state value indicative of the voltage level detected by the voltage detection circuit 502. The clock generator 504 generates clocks having different frequencies. The clock generator 504 includes a clock frequency selector 505 which selects the clock frequency at which the modem unit 501 to operate. The modem processor 507 carries out processings such as error correction, data compression and data expansion in addition to modulating the send data and demodulating the received data. The modem processor 507 includes a modem controller 516, a function processor 511 and a modem 509. The modem controller 516 includes a modem function determination circuit 508 and a message send circuit 514, and carries out the control functions of the modem unit 501. the modem function determination circuit 508 determines the function to be processed by the modem unit 501. The function processor 511 includes an error correction circuit 512 and a data compression/expansion circuit 513, and carries out functions other than modulation and demodulation, such as error correction and data compression/expansion. The error correction circuit 512 corrects the error in the data, and the data compression/expansion circuit 513 compresses and expands the data. The modem 509 includes a switching circuit 510 which switches the communication path to the remote end from the terminal equipment 506 to the modem function determination circuit 506 when notifying the mode of the modem unit 501 to the terminal equipment on the remote end. This mode indicates the selected functions such as the communication speed and error correction. The voltage detection circuit 502 constantly monitors the voltage from the battery 515, and outputs a voltage state value indicative of the detected voltage level. The voltage holding circuit 503 holds this voltage state value. The clock generator 504 selects the clock frequency which is used to drive the modem unit 501 depending on the voltage state value held in the voltage holding circuit 503. If the voltage level of the battery 515 is sufficiently high, the clock generator 504 selects a high clock frequency. On the other hand, the clock generator 504 selects a low clock frequency if the voltage level of the battery 515 is low. The modem processor 507 operates responsive to the clock pulses having the clock frequency which is selected by the clock frequency selector 505 of the clock generator 504. The modem function determination circuit 508 selects the required function or functions depending on the voltage state value and the function request information from the terminal equipment 506. For example, if the voltage level of the battery 515 is sufficiently high, it is possible to satisfy all of the required functions requested from the terminal equipment 506, and these functions are selected. On the other hand, if the voltage level of the battery 515 is low, the processing in the modem processor 509 is simplified so that a high-speed process can be carried out even in response to the low-clock frequency. In other words, if the terminal equipment 506 requests the error correction and the data compression/expansion, the modem function L determination circuit 508 determines whether to carry out only the error correction, to carry out only the data compression/expansion or not to carry out the error correction and the data compression/expansion, for example. If one of the error correction and the data compression/expansion is to be selected, the error correction is selected with a priority over the data compression/expansion. Prior to starting the communication, the modem function determination circuit 508 notifies the remote end of the determined processing function via the switching circuit 510 and the telephone line, so as to set the communication mode. In addition, the modem function determination circuit 508 also notifies the terminal equipment 506 of the set mode. The terminal equipment 506 makes the data communication with the terminal equipment on the remote end in accordance with the mode which is set by the modem unit 501. The function processor 511 inputs the function request information from the remote end via the switching circuit 510, and determines the function. In addition, based on the function request information from the terminal equipment 506, the function processor 511 supplies the processable function which is determined by the modem unit 501 depending on the voltage state value to the terminal equipment 506 via the message sending circuit 514. If a low function request is made from the terminal equipment 506 when the voltage level of the battery 515 is sufficiently high, that is, if the instruction from the terminal equipment 506 indicates that no error correction and no data compression/expansion are required, for example, the communication can be made at a sufficiently high speed even in response to low-frequency clock pulses. Hence, in this case, the modem function determination circuit 508 instructs the clock frequency selector 505 to select the low clock frequency, so as to extend the serviceable life of the battery 515. The modulation and demodulation operations of the modem 509 are the same as those of the conventional modem unit. In addition, the operations of the data compression/expansion circuit 513 and the error correction circuit 512 are the same as those of the conventional modem unit, except that the processing of the data compression/expansion circuit 513 and the error correction circuit 512 is started in response to the instruction from the function determination circuit 508. According to these embodiments, the modem unit 501 can operate even when the voltage level of the battery 515 decreases. In addition, the deterioration in the processing quantity caused by the decreased clock pulse frequency is compensated for by reducing the functions to be carried out, so as to enable a high-speed communication even when the clock pulse frequency is low. Furthermore, since the function selection can be made in steps, it is possible to carry out as much functions as possible depending on the voltage level of the battery 515. Moreover, if the terminal equipment 506 does not request high functions in a state where the voltage level of the battery 515 is high, it is possible to select the low clock pulse frequency so as to prevent unnecessary wear of the battery 515. Of course, it is possible to operate only the modem controller 516 in response to the clock pulses which are selected by the clock frequency selector 505, and operate the modem 509 in response to basic clock pulses. Next, a more detailed description will be given of the first embodiment, by referring to FIG.3 . In FIG.3 , a modem unit 520 and a terminal equipment 530 respectively correspond to the modem unit 501 and the terminal equipment 506 shown in FIG. 2. In 1 addition, a battery 521, a voltage detection circuit 522, a voltage state value holding circuit 524, a clock generator 525 and a modem processor 527 shown in FIG.3 respectively correspond to the battery 515, the voltage detection circuit 502, the voltage state value holding circuit 503, the clock generator 504 and the modem processor 507 shown in FIG.2. In this embodiment, a modem controller 528 of the modem processor 527 is driven by clock pulses which are selected depending on the voltage level of the battery 521. In addition, a modem 529 of the modem processor 527 is driven by basic clock pulses. This modem 529 is provided on an LSI which is independent of an LSI on which the remaining parts of the modem unit 520 are provided.. The voltage detection circuit 522 includes voltage comparators 523, 523' and 523''. The voltage comparator 523 compares the power source voltage from the battery 521 and a threshold value TH1, so as to detect the state of the power source voltage. For example, the voltage comparator 523 outputs a signal "1" if the power source voltage is higher than the threshold value TH1 and outputs a signal "0" if lower. Similarly, the voltage comparator 523' compares the power source voltage and a threshold value TH2, so as to detect the state of the power source voltage. The voltage comparator 523'' compares the power source voltage and a threshold value TH3, so as to detect the state of the power source voltage. The voltage holding circuit 524 holds the state of the power source voltage as the voltage state value depending on the outputs of the voltage comparators 523, 523' and 523''. For example, if the threshold values are such that TH1 > TH2 > TH3, the voltage state value is set to "011" when the power source voltage is lower than TH1 and higher than TH2. In this case, the state of the power source voltage can be held as a voltage state value having three stages. A reset signal *RST is supplied to the voltage state value holding circuit 524 and to the modem controller 528. The clock generator 525 includes an oscillator 525' and a frequency divider 526. The oscillator 525' generates basic clock pulses having a maximum clock pulse frequency of 30 MHz, for example. The frequency divider 526 frequency-divides the frequency of the basic clock pulses output from the oscillator 525' depending on the voltage state value which is held by the voltage state value holding circuit 524. For example, the frequency divider 526 generates clock pulses having clock frequencies of 30/n MHz, where n denotes the frequency dividing ratio. The modem processor 527 includes the modem controller 528, the modem 529 and a function processor 529'. The frequency divider 526 determines the frequency dividing ratio of the basic clock pulses depending on the voltage state value which is held in the voltage state holding circuit 524, and outputs the clock pulses having the frequency-divided frequency. For example, if the voltage level of the battery 521 is sufficiently high, the voltage state value is large, and the basic clock pulses having the frequency of 30 MHz is selectively output from the frequency divider 526 in this case. But if the voltage level of the battery 521 decreases, the voltage state value decreases, and the clock pulses having the frequency of 20 MHz is output from the frequency divider 526. Hence, the clock pulses having the maximum operable frequency is selected and output from the frequency divider 526 depending on the voltage level of the battery 521, that is, the power source voltage level. The voltage state value from the voltage state value holding circuit 524 is input to the input port of the modem controller 528. The modem controller 58 compares this voltage state mode and the function request from the terminal equipment 530, and sets the most appropriate operation mode, that is, the mode in which the most appropriate function process is selected. The modem controller 528 and the function processor 529' operate responsive to the clock pulses determined by the frequency divider 526. On the other hand, the modem 529 operates responsive to the basic clock pulses which have the frequency of 30 MHz and are output from the oscillator 525'. Next, a description will be given of an embodiment of the modem processor 527, by referring to FIG. 4 . In FIG. 4 , those parts which are the same as those corresponding parts in FIG.3 are designated by the same reference numerals, and a description thereof will be omitted. The modem controller 528 includes registers 540 and 541, a register comparator 542, a register 543, a function determination circuit 544, a command analyzer 545 and a message sending circuit 546. The modem 529 includes a switching circuit 547. The function processor 529' includes an error correction circuit 548 and a data compression/expansion circuit 549. In the modem controller 528, the register 540 stores the function request information which is received from the terminal equipment 530 via the command analyzer 545. The register 541 stores the voltage state value input from the voltage state value holding circuit 524. The register comparator 542 compares the contents of the registers 540 and 541. The register 543 stores the comparison result output from the register comparator 542. The function determination circuit 544 determines the function which is to be processed in the modem unit 520 depending on the content of the register 543. The error correction circuit 548 and the data compression/expansion circuit 549 are turned ON/OFF, that is, controlled to active/inactive state, depending on the determination result of the function determination circuit 544. The command analyzer 545 analyzes the function request information from the terminal equipment 530. In addition, when the command analyzer 545 receives from the terminal equipment 530 a query command of the function process which is determined by the function determination circuit 544, the command analyzer 545 controls the message send circuit 546 to transfer a message related to this function. The message send circuit 546 stores the information read out from the register 543 and send this information to the terminal equipment 530 depending on the function to be processed which is determined by the function determination circuit 544 or depending on the function information query command from the terminal equipment 530. Next, a description will be given of the operation of the system shown in FIG. 4 . The frequency divider 526 outputs the clock pulses having the frequency dependent on the voltage state value, and are supplied to the modem controller 528. The voltage state value held in the voltage state holding circuit 524 is input to the register 541 via the input port of the modem processor 527. On the other hand, the function request command from the terminal equipment 530 is input to the command analyzer 545, and the analyzed command is stored in the register 540. The register comparator 542 compares the values stored in the registers 540 and 541, and stores the comparison result in the register 543. For example, the register comparator 542 compares the voltage state value and the request value which is determined depending on the request from the terminal equipment 530. This request value has a large value when the function request is large such as the case where both the error correction and data compression/expansion are requested, and is small when the function request is small such as the case where there is no function request and both the error correction and data compression/expansion are unnecessary. The register comparator 542 selects the larger value and stores this value into the register 543. The function determination circuit 544 determines the function to be processed depending on the value stored in the register 543, and selects the function of the function processor 529'. If the error correction is required, the function determination circuit 544 turns ON a start signal which is supplied to the error correction circuit 548, and the function determination circuit 544 otherwise turns this start signal OFF. In addition if the data compression/-expansion is required, the function determination circuit 544 turns ON a start signal which is supplied to the data compression/expansion circuit 549, and the function determination circuit 544 otherwise turns this start signal OFF. Prior to making the data communication, it is necessary to notify the terminal equipment on the remote end the functions of the terminal equipment 530. Hence, the switching circuit 547 switches the communication path from the path to the telephone line to the path from the terminal equipment 530 to the function determination circuit 544. The function determined by the function determination circuit 544 is notified to the remote end, and the remote end carries out a control so as to make the processing by the same function. Such a control may be realized according to the CCITT Recommendations V.42/42bis. The function determination circuit 544 notifies the terminal equipment 530 of the function which is determined as a result of the communication with the remote end, as an indication message. The function determination circuit 544 also inputs the function request information from the remote end via the switching circuit 547, and determines the function. In this state, the terminal equipment 530 cannot confirm whether the message which is received as the indication message is caused by the active selection of the modem unit 520 or by an erroneous operation. Hence, the function determination circuit 544 sends to the message send circuit 546 a function selection message which indicates that the indication message is caused by the active selection of the function determination circuit 544. The message end circuit 546 sends this function selection message to the terminal equipment 530. When the command analyzer 545 receives from the terminal equipment 530 a query command of a function which can be processed by the modem unit 520, the command analyzer 545 reads the value stored in the register 543 into the message send circuit 546. The message send circuit 546 then sends the content of the register 543 to the terminal equipment 530. Next, a more detailed description will be given of the second embodiment, by referring to FIGS. 5 and 6 . FIG. 5 shows the second embodiment, and FIG. 6 shows an embodiment of the modem controller 528 shown in FIG. 5 . In FIGS. 5 and 6 , those parts which are the same as those corresponding parts in FIGS.3 and 4 are designated by the same reference numerals, and a description thereof will be omitted. In this embodiment, a determination result which is related to the function to be processed and is made in the function determination circuit 544 of the modem controller 528 is reflected to the selection of the frequency dividing ratio in the frequency divider 526. In other words, the voltage state value holding circuit 524 includes a voltage state value selection circuit 524' which selects a voltage state value corresponding to the determination result made in the function determination circuit 544. The selected voltage state value is supplied to the frequency divider 526. If the power source voltage is high and the voltage state value is large, the content of the register 543 is reflected to the selection of the frequency dividing ratio of the frequency divider 526 when the request value from the terminal equipment 530 is small. In other words, the voltage state value selection circuit 524' compares the value of the register 543 referred to by the function determination circuit 544 and the value which is input to the voltage state value holding circuit 524 from the voltage detection circuit 522. If the value of the register 543 is smaller than the voltage state value detected by the voltage detection circuit 522, the content of the register 543 is selected and output from the frequency divider 526. The frequency divider 526 outputs clock pulses having a low frequency depending on the function which is determined by the function determination circuit 544. As a result, if the power source voltage is sufficiently high and the function request from the terminal equipment 530 is small, the clock pulse frequency is kept low so as to prevent unnecessary wear of the battery 521. Otherwise, the operation of this embodiment is basically the same as that of the first embodiment. Therefore, according to the first and second embodiments, the communication will not be disabled immediately when the power source voltage of the modem unit decreases. Instead, the functions of the modem unit are automatically adjusted so that the communication can be continued with the reduced power source voltage, and the communication can be made at a low power consumption. Accordingly, the modem unit can be used for a longer period of time after the power source voltage begins to decrease. Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention.

Claims: A modem unit adapted to be coupled between a land or radio telephone line and terminal equipment, said modem unit comprising modem circuit means (8,27,85,507), coupled to the terminal equipment (250,251,506), for modulating data received from the terminal equipment and for demodulating data transmitted to the terminal equipment, and isolation means (C1,C2,34), coupled to said modem circuit means (8,27,85,507), for providing DC isolation between the telephone line and the terminal equipment (250,251,506), said modem circuit means and said isolation means being respectively provided on a single modem integrated circuit card; characterised in that there are further provided: a battery (515) for supplying power to various parts of the modem unit; detection means (502); coupled to said battery, for detecting an output voltage level of said battery; and selection means (504), coupled to said detection means, for selecting a frequency of a clock which drives said modem circuit means depending on the voltage level detected by said detection means, said modem circuit means (507) including determination means (508), coupled to said detection means, for determining a modem function of said modem circuit means based on the voltage level detected by said detection means and function request information specified from the terminal equipment (506). The modem unit as claimed in claim 1, characterised in that said modem circuit means (507) includes switching means (510), coupled to said determination means (508), for switching a communication path to the telephone line from the terminal equipment (506) to said determination means so as to notify the modem function determined by said determination means to a terminal equipment on a remote end. The modem unit as claimed in claim 1 or 2, characterised in that said modem circuit means (507) includes send circuit means (514), coupled to said detection means (503), for notifying the terminal equipment (506) of a modem function which can be processed depending on the voltage level detected by said detection means (502), said send circuit means adapted to notify the modem function determined by said determination means (508) prior to a start of a data communication or responsive to a request from the terminal equipment. The modem unit as claimed in any of claims 1 to 3, characterised in that said selection means (504) adapted to input function information determined by said determination means (508) and selectively output a clock having a frequency lower than normal depending on the modem function if said determination means determines this modem function responsive to a request from the terminal equipment (506). The modem unit as claimed in any of claims 1 to 4, characterised in that said modem circuit means (507) comprises: a modem (509) carrying out modulation and demodulation of signals based on a basic clock; a function processor (511), coupled to said modem, carrying out functions other than the modulation and demodulation; and a modem controller (516), coupled to said detection means (502), said selection means (504) and said function processor, controlling said function processor, and that said modem controller (516) operate in response to a clock which is determined based on the voltage level detected by said detection means (502) or the modem function determined by said determination means (508).

Inventors: ARAI YASUHIRO, MARUO NOBUHIDE, NARITA YOSHIAKI, ARAI, YASUHIRO, MARUO, NOBUHIDE, NARITA, YOSHIAKI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1993
Main classification: H04M11
IPC codes: H04M11, H01M2