Abstract: A serial data generating circuit and a key input signal generating circuit are provided at a panel substrate side, and input key data are transmitted in series to a main substrate side of a telephone apparatus. The number of signal lines connected between the panel substrate and the main substrate are reduced. Further, on the main substrate side downstream of a selection circuit, a data converting and producing circuit which converts the serial input key data into parallel dial data is provided to permit switching of the signal source between a processor and the panel substrate to thereby enable a dial call origination even during a power failure condition.

Abstract: A DTMF signal generating circuit for producing output of a selection signal having a frequency corresponding to a signal entered from push buttons. A high frequency oscillation signal output from an oscillatory circuit are delivered to both a first frequency dividing circuit for dividing high frequency signals by a first dividing ratio and a second frequency dividing circuit for dividing high frequency signals by a second dividing ratio, thereby producing two kinds of divided signals each of which has its own predetermined frequency. A fractional frequency division is then accomplished by switching from an output of a first frequency dividing circuit to an output of a second frequency dividing circuit at a predetermined timing. The signals output form the switch are then counted by a ROM address counter, producing an output of an address value signal.

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

Abstract: A dialer circuit comprising a microcomputer for controlling the dialing of a telephone. This dialer circuit is capable of storing a telephone number and transmitting a signal concerning this telephone number to a telephone circuit according to a given command. The dialer circuit is equipped with a means for detecting the ON state or the OFF state of a hook switch; upon detection of the state of the hook switch, the dialer circuit performs a resetting of the entire system except a memory in which the telephone number is stored. The result is that when operating the hook switch, it is possible to automatically reset only the system, thus effectively preventing any reckless driving of the system.