| 摘要 |
<p>PURPOSE:To provide the voltage detection system which can adjust manufacture variance of a semiconductor by itself by utilizing clock-cycle-to-battery-output- voltage characteristics of a built-in CR oscillation circuit mounted on the same chip. CONSTITUTION:At the time of replacement with a brand-new battery 22, an interruption period by a current battery voltage is observed by software. A CPU 11 finds an estimated oscillation period at voltage detection level by function approximation on the basis of previously evaluated characteristics of the battery voltage to the oscillation period of the internal CR oscillation circuit 14, and holds the result in a memory part 19 until next battery replacement. A user when using a voltage detection circuit measures the interruption period at the current battery voltage by the same method with initial setting. Then this measured period is compared with the estimated period which is previously estimated and stored at the time of the initial setting. When the CR oscillation period is larger than the set value, it means that a desired battery voltage level to be detected is reached; and an alarm display is made and battery replacement, etc., is performed.</p> |
