Patent ID: 7257323

Claim:
A signal-off detection circuit counting input data signals per a fixed time for detecting a disconnection state of said data signal according to whether the count value reaches a predetermined value (a positive integer greater than 1), the circuit comprising: a counter for counting said input data signals every fixed time and causing transition of its output level when reaching to said predetermined value; a first flip flop taking a predetermined level of said counter at the timing of the output level transition thereof and holding it for said fixed time; a second flip flop taking the holding level of the first flip flop every said fixed time and holding it; means for generating a reset pulse for resetting said counter and said first flip flop every said fixed time; delay means for delaying a data-taking-in timing pulse by a predetermined time to output as said reset pulse; wherein the holding output of the second flip flop is used for an alarm output, and wherein said data-taking-in timing pulse is also used as the data-taking-in timing pulse for said second flip flop.