Abstract: A key telephone system includes a main unit, a DSS interface, and a detector. The main unit includes a speech path switch, a plurality of call processing interfaces, an operating data memory, operation mode setting switches, and a controller for controlling the speech path switch by referring to the operating data memory when data transmission is periodically performed between the plurality of key telephone sets through the call processing interface in the call processing mode, and for updating contents of the operating data memory according to operating data externally input in the data setting mode. The DSS interface connects at least one DSS console. The detector detects that first normal data received, after a periodic data transmission with the DSS console through the DSS interface is an abnormal transmission for a predetermined period of time, is data unique to the key telephone set.

Abstract: A key telephone system includes a temporary registration memory for temporarily storing operating data and a final registration timing data memory for storing final registration timing data, including a timing condition for transferring contents of the temporary registration memory to the operating data memory. Operating data input by a user and the final registration timing data are written into the temporary registration memory and the final registration timing data memory, respectively, from a data input unit connected to the main unit during a data setting mode. The system discriminates establishment of the timing condition designated in accordance with the final registration timing data stored in the final registration timing data memory, whereupon the operating data stored in the temporary registration memory is transferred to the operating data memory.

Abstract: A key telephone system includes a plurality of key telephone sets having speakers and tone signal generators and communicating with each other through extension links. The key telephone system further includes a first memory, a second memory, a main CPU, a sub CPU, an MF signal generator, and a speech path switch. The first memory stores availability of the extension links. The main CPU discriminates whether all extension links are available according to the storage contents of the first memory in an extension call mode. The MF signal generator signals to a calling key telephone set that all the extension links are busy when the main CPU discriminates that all the extension links are busy. A second memory stores information on each calling and called key telephone set if the extension call is in a state where the MF signal generator signals that all the extension links are busy.

Abstract: There is disclosed a data transmitting and receiving circuit extremely advantageous when applied to a key telephone system. The data transmitting circuit comprises a voltage dividing circuit for dividing a power supply voltage to apply the divided voltage to one end of a primary winding of a transformer, and a driver circuit comprising a pair of transistors connected in series between the power supply and a common potential terminal, the node of the transistors being connected to the other end of the primary winding of the transformer. When data signal is transmitted, the data transmitting circuit is operative to complementarily turn and off the pair of transistors in accordance with the data signal. In contrast, when data is not transmitted, the data transmitting circuit is operative to cut off both the transistors. Thus, the data transmitting circuit can eliminate the possibility that a DC voltage on which a data signal to be transmitted is superimposed undesirably changes.

Abstract: In a key telephone system with a plurality of four-wire key telephone sets wherein a two-wire telephone set is connected to a main control device via a pair of speech lines so that intercom speech and office line speech are possible between the two-wire telephone set and other key telephone sets, the improvement wherein said main control device comprises a call signal generating circuit, first transfer switching means for transfer-connecting said speech lines between a pair of office speech lines and a pair of intercom speech lines, second transfer switching means for transfer-connecting said speech lines between said call signal generating circuit and said first transfer switching means, DC loop supervisory means for supervising a DC loop of said speech lines, and a control circuit inputted with an output of said DC loop supervisory means for controlling said first and second transfer switching means in accordance with the states of said office lines.

Abstract: In a signal transmission system of a key telephone system of the type comprising a main device connected to office lines and having an input/output port for transmitting and receiving signals, and a plurality of key telephone sets connected in parallel to the main device through a pair of signal lines for transmitting and receiving various control signals between the main device and the key telephone sets, wherein each of the control signals is constituted by a pulse width modulated time series signal of a predetermined number of bits, respective control signals are inputted and outputted in parallel to and from a bit input/output of the input/output port and wherein transmission and reception of the control signals between the main device and respective key telephone sets are simultaneously performed by parallel input/output operations of the calculating processing unit.