| 摘要 |
PROBLEM TO BE SOLVED: To obtain a switch device of simple constitution which does not malfunction against an external noise by detecting a signal break according to a signal generated by converting a clock signal through a wired OR. SOLUTION: The output of a buffer 35 varies between 'high impedance' a 'L' corresponding to 'H' and 'L' of the clock signal CLK0. The output of the buffer 35 is inputted to a break detector 26 through the wired OR consisting of a pull-up resistor 30 together with the output of a buffer 41. The break detector 26 consists of a one-shot multivibrator and outputs a pulse having specific width when the input level varies periodically, but holds the output at 'H' unless the input varies for longer than a certain time. For example, when the clock signal CLK0 is fixed at 'L', the output of the break detector 26 goes up to 'H', so a switching control circuit 21 controls selectors 32 and 38 to switch the signal to a normal clock signal CLK1. |
