Tamura Electric Works, Ltd.

Junzo Kikuchi

Ryuzo Sugiura

Toshiro Yoshida

Yoshihiro Ikeda

Chuta Aikawa

Tomio Nishimura

Noriyoshi Sanada

Masaki Kuroda

Kouji Tanaka

Hikaru Sano

Mitsuyoshi Murakami

Mutsuhiro Yamamoto

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. Further, the data receiving circuit comprises a voltage divider common to the above-mentioned voltage dividing circuit, a comparator having a comparison input connected to the other end of the secondary winding of the transformer, and a reference voltage supply circuit for selecting either of two reference voltages depending upon a binary output level of the comparator to deliver the selected one to the reference input of the comparator. Thus, the data receiving circuit can provide a stable and steady receiving condition when a data signal superimposed on a DC voltage is received to change the data signal into a binary received signal.

Key telephone system

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. Under a normal state the speech lines are connected to the intercom speech lines through the first and second transfer switching means. At the time of arrival of an office line call signal the second transfer switching means is switched to send the call signal to the speech lines. Thereafter the second transfer switching means is reset and the first transfer switching means is switched to the office line speech lines in accordance with the output of the loop supervisory means.

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.

Control of a key telephone system using a pulse width modulated signal

A key telephone exchange system comprises office line units connected to office lines, terminal units respectively connected to key telephone sets and a main control unit for changing connections between respective office line units and respective terminal units. Each office line unit comprises a first memory device to store data transmitted between the office line unit and an office line, and a first processor for writing and reading data into and out of the first memory device for controlling origination and call requests to and from the office line. Each terminal unit comprises a second memory device adapted to store data transmitted between a terminal unit and a key telephone set, and a second processor for writing and reading data into and out of the second memory device for controlling transmission of data between a terminal unit and a corresponding key telephone set. The main control unit comprises a third memory device for storing states of use of the terminal unit and of the office line unit, and a third processor which sequentially scans data in the first and second memory devices of the terminal unit and of the office line unit and for exchanging connections between the terminal units and the office line units according to data obtained as a result of the scanning.

Key telephone system with multiple processor control

Growing community of inventors

Kawasaki, Japan

Junzo Kikuchi