OFFICE LINE OCCUPATION STATE DISPLAY TELEPHONE AND THE CONTROL METHOD THEREOF

PURPOSE: An office line occupation state display telephone and a control method thereof are provided to detect and display the use state of the office line by a microcomputer, thereby preventing the occupation states of plural telephones. CONSTITUTION: Filters(L1)(L2) removes noise of input and output signals. A ring sensor(100) senses incoming of ring signal through the office line. A hook relay(110) connects the telephone to the office line, thereby occupying the office line. A transformer(120) separates AC and DC flowing the office line. A DC holding unit(130) forms a loop of DC current flowing the office line, so separates the DC current and outputs different level voltages according to the DC level of the office line. A hook switch(140) senses on/off of a receiver. An LCD(150) displays the present state of the telephone. A memory(160) stores the basic state value of the office line. A microcomputer(170) controls the operation of each device, discriminates whether the other office line is occupied or not according to the output voltage level and displays the result to the LCD(150) after in the state that the office line is not occupied, the DC current is set as basic state value.