Electrical pulse counters – pulse dividers – or shift registers: c – Systems – Identifying or correcting improper counter operation
Patent
1991-01-23
1992-10-20
Heyman, John S.
Electrical pulse counters, pulse dividers, or shift registers: c
Systems
Identifying or correcting improper counter operation
377 39, 328138, 328133, 328140, H03K 2140, H03K 5153
Patent
active
051576996
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 normal conditions. A discrimination circuit is connected to monitor the outputs of the scale of N.sub.5 and N.sub.6 counters to determine the presence of a fault by detecting when either output no longer meets the associated relationship.
REFERENCES:
patent: 3723889 (1973-03-01), Oberst
patent: 3873928 (1975-03-01), Lafuze
patent: 4089060 (1978-05-01), Mitchell
patent: 4255809 (1981-03-01), Hillman
patent: 4468796 (1984-08-01), Suga
patent: 4649886 (1987-03-01), Igashira et al.
patent: 4686483 (1987-08-01), Isshiki et al.
Handa Masaaki
Miyazaki Hajime
Muranaka Tsukasa
Uehara Taisuke
Heyman John S.
Ogrod Gregory D.
Seiko Epson Corporation
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