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 system for transmissing data by a pulse signal through a pair of lines connected between a main unit and a key telephone set is disclosed. The main unit includes a transmitter for sending, prior to transmission of pulse train data, a start signal of a pulse train including a pulse of an n-bit (where n is an integer) specific logic value and a pulse of an (n+1)-bit logic value opposite to the specific logic value. The key telephone set includes a change detector for detecting a change in the pulse train of the start signal in a direction of the logic value opposite to the specific logic value, a logic value detector for detecting a logic value of an (n+1)th bit pulse from a detection timing of the change detector, a discriminator for discriminating on the basis of the logic value of the (n+1)th bit pulse whether a line connection for the key telephone set is normal, and a reader for reading data following the start signal according to a logic determined by a discrimination result.

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: Disclosed is a system for transmitting data by a data pulse train obtained by a combination of "0" or "1" bit pulse signals through a pair of lines connected beween a main unit and a key telephone set. The system includes a counter for sampling the pulse train and counting "0" or "1" bit pulse signals; a comparator for comparing a count of the counter with a reference value; and a correcting section for adding "0" or "1" correction pulses so as to set the count to be the reference value when the count is different from the reference value.