Watchdog timer employing plural counters and discriminator for determining normal operating frequency range of input
US5157699A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 23, 1991 |
| Grant date | Oct 20, 1992 |
| Priority date | — |
| Expiry date | Jan 23, 2011 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH10N30/802
- WIPO fieldEngines, pumps, turbines
- WIPO sectorMechanical engineering
Abstract
A watchdog timer capable of detecting clock signals when the opening frequency of a frequency source drifts lower or higher than a normal desired operating range, increasing circuit safety and reliability. The timer uses first and second clock oscillation circuits to generate first and second signals of frequencies f.sub.1 and f.sub.2 which are then divided by 1/N.sub.1 and 1/N.sub.2 in first and second frequency dividers, respectively. Third and fourth frequency dividers are used to divide the second frequency signal f.sub.2 by 1/N.sub.3 and 1/N.sub.4, respectively. A scale of N.sub.5 counter is connected to receive the f.sub.1 /N.sub.1 frequency signal as a clock input and the f.sub.2 /N.sub.3 frequency signal as a reset input, and provides an output signal at a frequency of (f.sub.1 /N.sub.1)/N.sub.5 which is less than f.sub.2 /N.sub.3 when the clock circuits are operating under normal conditions. A scale of N.sub.6 counter is connected to receive the f.sub.2 /N.sub.4 frequency signal as a clock input and the f.sub.1 /N.sub.2 frequency signal as a reset input, and provides an output signal at a frequency of (f.sub.2 /N.sub.4)/N.sub.6 which is less than f.sub.1 /N.sub.2 under nor…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.