Plural oscillator circuit arrangement for rapidly resetting a co

Details Plural oscillator circuit arrangement for rapidly resetting a co Plural oscillator circuit arrangement for rapidly resetting a co

1992-02-03

1993-03-23

Grimm, Siegfried H.

Oscillators

Plural oscillators

Selectively connected to common output or oscillator...

36493451, 3649344, 364DIG2, G06F 108, G06F 124, H03B 100, H03L 300

Patent

active

051968100

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a circuit arrangement for rapidly generating an oscillating electrical input signal at a predetermined frequency for input to a computer circuit means and, more particularly, to a circuit arrangement for rapidly resetting the computer circuit means with the oscillating electrical input signal. A circuit arrangement for resetting microprocessors has already been suggested in DE-OS 31 19 117. In this circuit arrangement the output signal of the clock generator is used for the purpose of resetting. To do this, the output signal of the clock generator is rectified and fed to the reset input of the microprocessor. When the supply voltage is switched on, the resetting process of the microprocessor is only concluded when the clock generator of the microprocessor has already begun to oscillate. Undefined states which can occur e.g. when the microprocessor is reset in a voltage-dependent manner but the clock generator has not begun to oscillate are accordingly reliably prevented. But such a resetting process can be of quite long duration under certain circumstances, particularly when generators are used which begin to oscillate only very slowly, e.g. quartz oscillators. Further, a circuit which is already known from the Siemens microcontroller 80C 517 has, in addition to a quartz oscillator, an RC oscillator which serves to monitor the quartz oscillator.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved circuit arrangement for supplying an oscillating electrical signal at a predetermined frequency to a computer circuit means advantageously for resetting a computer circuit, which does not have the above-mentioned disadvantage.
According to the invention the circuit arrangement for supplying an oscillating electrical signal at a predetermined frequency to computer circuit means comprises a voltage supply means for supplying a voltage; a first oscillator means connectable with the computer circuit means and the voltage supply means and being operable to produce a first oscillating electrical output signal when the voltage from the voltage supply means is applied thereto; a second oscillator means connectable with the voltage supply means and the computer circuit means and operable to produce a second oscillating electrical output signal and being structured to begin oscillating more quickly than the first oscillator means when the voltage of the voltage supply means is applied thereto (i.e. the frequency of the second oscillator increases more rapidly than that of the first oscillator when voltage is applied to it); means for connecting the second oscillator means with the computer circuit means acting to connect the second oscillator means and the computer circuit means when the voltage from the voltage supply means is greater than a preset minimum supply voltage and is applied to the second oscillator means; and means for connecting the first oscillator means with the computer circuit means after a predetermined time period beginning at a time of connection of the second oscillator means with the computer circuit means.
Advantageously in a preferred embodiment of the invention the first oscillator comprises a quartz oscillator and the second oscillator comprises an RC oscillator.
In contrast, the circuit arrangement according to the invention has the advantage that it is possible to set the computer circuit in operation very quickly since the computer circuit is first operated with an oscillator which begins very quickly to oscillate, but is possibly more unstable with respect to frequency, and is only then switched to an oscillator which slowly begins to oscillate, preferably a quartz oscillator which takes longer to start oscillating. Because of this step it is possible to set the computer circuit in operation very quickly at the occurrence of supply voltage so that the initialization process of the computer circuit has already been concluded when switching to the quartz oscillator. The step according to the inv

REFERENCES:
patent: 4868525 (1989-09-01), Dias
patent: 5126695 (1992-06-01), Abe

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