US 5,969,558 A · Abnormal clock signal detector and switching device

Abstract

A system clock signal switching device capable of switching outputs from a plurality of clock signal generation systems i order to ensure the continuous supply of a stable system clock signal. An oscillation circuit A generates a clock signal CK1 as an ordinary system clock signal while an oscillation circuit B generates a clock signal CK2 as another separate clock signal, such as the time-count clock signal. The output lines of these circuits are connected with the input terminals of a multiplexer. An output clock signal monitor circuit checks the clock signal CK1 from the oscillation circuit A, wherein input terminals of the monitor are connected with the output lines to attain the operational clock signals for its monitoring operation. A monitor flag from the monitor circuit is supplied to a switching signal input terminal of the multiplexer via a line. An output line of the multiplexer is provided to a subsequent circuit using the system clock signal while the output line of the oscillation circuit B is provided to the subsequent circuits such as a time-count circuit.

Claims14

Dependent claims

A system clock signal switching device, comprising:

a plurality of clock signal generators for generating a respective plurality of clock signals, including a first clock signal generator for generating an observed clock signal and a second clock signal generator for generating a substitute clock signal;
a monitor device to receive the observed clock signal and the substitute clock signal, for monitoring the observed clock signal to detect an abnormality in the observed clock signal;
a multiplier that adjusts the frequency of the substitute clock signal to provide an adjusted substitute clock signal having a frequency that is substantially the same as a frequency of the observed clock signal;
and
a clock signal switch that provides an output clock signal, wherein the output clock signal corresponds to the observed clock signal if the abnormality is not detected by the monitor device and wherein the output clock signal corresponds to the adjusted substitute clock signal if the abnormality is detected by the monitor device.

2 more elements

Dependencies are inferred from the claim text.

Abnormal clock signal detector and switching device

Life of this patent

Abnormal clock signal detector and switching device

Life of this patent

Abstract

Claims14