Telephone system for transmitting either a dial pulse or a dual-tone multi-frequency signal along a telephone line

Abstract: A telephone system for transmitting either a dial pulse signal or a dual-tone multifrequency signal along a telephone line. This telephone system includes a switching means for changing between a KEY signal from a key board and a control signal from a CPU. When a power interruption sensing means senses that the external power voltage is below a predetermined voltage, the switching means shunts from the control signal to the KEY signal and transmits either the DTMF signal or the DP signal along the telephone line.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: This invention relates to a telephone system, and more particularly to a multifunction telephone system having functions such as a facsimile transmission and automatic recording. 2. Description of the Related Arts: In recent years, with the progress in the public telephone network, the development of telephone systems having the functions of facsimile transmission and automatic recording have been popular. In this type of telephone system, it is necessary to incorporate a central processing unit (hereinafter referred to as a CPU) having the capacity of processing signals in order to realize an apparatus compact in size and having a lot of functions. Fig. 2 of the accompanying drawings is a schematic diagram showing the circuit configuration of a conventional telephone system. A KEY signal output from a keyboard 3 of a telephone system 1 is transferred to a CPU 4 which controls the operation of the entire telephone system. The CPU 4 outputs a CPU signal, which is a control signal, to an input controller 21 in a selected signal transmitting circuit 2 in response to the input of the KEY signal. The selected signal transmitting circuit 2 consists of a single-chip large scale integrated circuit (hereinafter referred to as an LSI), and the input controller 21 outputs dial data to both a dual-tone multifrequency (hereinafter referred to as a DTMF) signal generator 24 and an output controller 25 in response to the CPU signal. The DTMF signal generator 24 outputs a DTMF signal composed of a combination of two frequencies on the basis of the input dial data along a telephone line. At the same time, the output controller 25 outputs a dial pulse (hereinafter referred to as a DP) signal along the telephone line on the basis of the input dial data. The selected signal transmitting circuit 2 further includes a memory 23 which stores the dial data output from the input controller 21 and outputs the dial data that has been stored and is read out again at the time of redialing to both the DTMF generator 24 and the output controller 25. The controller CPU 4 is driven by an external power supply of +5V, while each component in the selected signal transmitting circuit 2 is driven by a telephone line current acquired from the telephone line via a resistor 29 and a diode 28. Thus, in the conventional telephone system 1, the CPU 4 processes the KEY signal entered from the keyboard 3 and outputs a control signal to the selected signal transmitting circuit 2, and then transmits either the DTMF signal or the DP signal along the telephone line. In the case where the external power supply drops due to, for example, a power failure, the CPU 4 will not operate on the telephone line current due to the large power dissipation of the CPU. As alternatives, it may be considered that the KEY signal is directly delivered from the keyboard 3 to the input controller 21 in the selected signal transmitting circuit 2. In such a circuit configuration, however, it is difficult to effect a compaction function by which a given telephone number is defined by a predetermined compacted telephone number and output to the input controller 21 because the KEY signal is not processed by the CPU 4. The article "Special Requirements and LSIs for Telephone Sets" by Y. Nishino, disclosed on pages 413 to 422 of IEEE TRANSACTIONS ON CONSUMER ELECTRONICS, Vol. CE-33, No. 3, August 1987, New York, NY, US, discloses a telephone system according to the preamble of claim 1. The central processing unit forms part of a separate repertory dialing control circuit and the external power supply is provided for a one-touch dialing number memory and a clock display in order to ensure certain background functions even when the telephone system is in ON HOOK mode. Furthermore, an interface circuit is provided between a repertory dialing control circuit and a selected signal transmitting means, which sends signals equivalent to the touch of the keyboard keys to the selected signal transmitting means. Accordingly, a key signal from the keyboard is supplied to the selected signal transmitting means directly and also via the central processing unit and the interface circuit. As both key signals are supplied to the selected signal transmitting means, it is necessary to indicate whether the repertory dialing signal from the CPU is allowable. A malfunction of a repertory dialing circuit may either be caused by a CPU disorder or by a loss of battery power which leads to a loss of the one touch dial information stored in the one-touch dialing number memory. In order to ensure that manual dialing is still possible in case of such malfunctions, a control circuit is provided in the interface circuit which instructs the selected signal transmitting means, i.e. dial signal generator, to accept input signals from the dial key only. The above described repertory dialing telephone requires a complex arrangement with a separate repertory dialing circuit, dial pulse circuit and connection circuit. It is an object of the present invention to provide a telephone system which basically functions even when the batterie power is lost and which has a reduced complexity. This object is achieved by a telephone system as claimed in claim 1. According to the claimed arrangement, the key signal from the keyboard is converted into a dial signal and subsequently switched in dependence on the voltage level of the power supply. Thus, even in case of CPU malfunctions due to drop in the voltage level, a dial signal is available, such that additional key interface circuits for converting key signals into dial signals are not required in the DTMF signal generator or the pulse dialer. Furthermore, a simple changeover switching means can be employed which switches either the dial signal from the input controlling means or the dial signal from the CPU to the selected signal transmitting means. BRIEF DESCRIPTION OF THE DRAWINGS The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as other features and advantages thereof will be best understood by reference to the detailed description which follows, read in conjunction with the accompanying drawings, wherein: Fig. 1 is a block diagram showing the circuit configuration of a telephone system according to this invention; and Fig. 2 is a block diagram showing the circuit configuration of a conventional telephone system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, a telephone system embodying the present invention will be described hereunder. Fig. 1 is a block diagram showing the circuit configuration of the telephone system according to one embodiment of this invention. A KEY signal entered from a keyboard 3 is transferred to an input controller 21 inside of a selected signal transmitting circuit 2. The input controller 21 distributes the received KEY signal as dial data, and outputs one of the distributed dial data to a CPU 4 for controlling the telephone system 1. The CPU 4 outputs a CPU signal at the "b" terminal of a changeover switch 22 in the selected signal transmitting circuit 2. The remaining dial data that is distributed by the input controller 21 is transferred to the "a" terminal of the changeover switch 22. This changeover switch 22 is connected to a DTMF signal generator 24, an output controller 25 and a memory 23. The telephone system 1 also includes a power interruption sensing means 5, which is connected to an external power +5V via a diode 26, for sensing the voltage drop in an external power supply to a value below a predetermined value. The changeover switch 22 is controlled by a KEY/CPU signal representative of the sensing signal from the power interruption sensing means 5. Namely, if the power supply voltage is below a predetermined level, the changeover switch 22 changes a contact point thereof to the side "a" in order to output the dial data from the input controller 21, whilst if the power supply voltage is above a predetermined level, the changeover switch 22 switches the contact point to the side "b" to issue the CPU signal from the CPU 4. The dial data output from the changeover switch 22 is transferred to both the DTMF signal generator 24 and the output controller 25, and then either a DTMF signal or a DP signal is transmitted along the telephone line. The dial data from the changeover switch 22 is stored in the memory 23, and in the case of redialing, this dial data is read out and output to both the DTMF signal generator 24 and the output controller 25. A drive current is supplied to both the CPU 4 and each component in the selected signal transmitting circuit 2 by way of diodes 26 and 27, respectively. Each component in the selected signal transmitting circuit 2 has an alternative power supply of a telephone line current acquired from the telephone line through a resistor 29 and a diode 28. These diodes 27, 28 and the resistor 29 constitute a diode switch 31. With such a circuit configuration, if the power supply drops below a predetermined voltage, the telephone line current is supplied to the selected signal transmitting circuit 2 via the resistor 29 and the diode 28, and then, by the use of the KEY signal from the keyboard 3 along the telephone line, either the DTMF signal or the DP signal will be transmitted . Thus, in the embodiment of the present invention, even if the CPU becomes inoperative due to the voltage drop in the external power supply, it is possible to transmit the DTMF signal and the DP signal by the utilization of the telephone line current, and when the external power supply is in a normal range, it is possible to change the definition of the KEY signal by processing the KEY signal from the keyboard with the CPU. A telephone system for transmitting either a dial pulse signal or a dual-tone multifrequency signal along a telephone line. This telephone system includes a switching means for changing between a KEY signal from a keyboard and a control signal from a CPU. When a power interruption sensing means senses that the external power voltage is below a predetermined voltage, the switching means shunts from the control signal to the KEY signal and transmits either the DTMF signal or the DP signal along the telephone line.

Claims: A telephone system comprising: a) a keyboard ( 3 ); b) a power interruption sensing means ( 5 ) for sensing a drop in an external power supply voltage below a predetermined voltage level; c) a selected signal transmitting means ( 2 ) comprising an output means ( 30 ) for outputting either a dual-tone-multifrequency signal or a dial pulse signal; and d) a central processing unit ( 4 ), characterized in that e) switching means ( 31 ) are provided for switching a drive current supply of said selected signal transmitting means ( 2 ) from said external power supply to a telephone line current if said external power supply voltage drops below said predetermined voltage level; and that f) said selected signal transmitting means ( 2 ) further includes: fl) an input controlling means ( 21 ) for receiving a signal from said keyboard ( 3 ) and for outputting a dial signal supplied to said central processing unit ( 4 ); and f2) a changeover switching means ( 22 ) for receiving said dial signal and a signal issued from said central processing unit ( 4 ) in response to said dial signal and for outputting either said dial signal or said signal from said central processing unit ( 4 ) in response to a signal from said power interruption sensing means ( 5 ), wherein said output means is arranged to output said dual-tone-multifrequency signal or said dial pulse signal in response to the output signal of said changeover switching means ( 22 ). A telephone system according to claim 1, characterized in that said changeover switching means (22) is arranged to output said dial signal from said input controlling means (21) if it is sensed by said power interruption sensing means (5) that said external power supply voltage drops below said predetermined voltage level and to output said signal issued from said central processing unit (4) when said external power supply voltage is above said predetermined voltage level. A telephone system according to claim 1, characterized in that said switching means (31) comprises a plurality of diodes (27, 28) connected with each other in parallel.

Inventors: SAJI MITSURO, SAJI, MITSURO, Saji, Mitsuro, c/o Rohm Co., Ltd.
Applicants: ROHM CO LTD, ROHM CO., LTD.
Application year: 1991
Main classification: H04M19
IPC codes: H04M1, H04Q1