Programmable time base circuit with protected internal calibration
First Claim
1. A time base circuit provided with internal calibration, comprising:
- oscillator means for providing an output signal having a predetermined operating frequency;
programmable counter means for receiving the output of said oscillator means and dividing said operating frequency by a factor of n to provide a reference signal operating at a reference frequency;
storage means for receiving from an external source the value of n for storage thereof and for interface of the stored value of n with said programmable counter means; and
inhibit means for inhibiting change of the value of n in said storage means after storage thereof;
said reference frequency being a calibrated value and determined after measurement of said output signal from said oscillator means, such that said programmable counter means provides an internal calibration capability.
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Accused Products
Abstract
A timeout circuit with internal calibration includes an oscillator (11) for generating an initial frequency for division by a modulo-n counter (20). The counter (20) receives the value of n from a calibration register (22) and divides the frequency of the oscillator by the value of n. A gate (26) prevents alteration of the contents of the register (22). The output of the counter (20) provides a calibrated frequency which is further divided by a day counter (32) for output to a countdown counter (34). The countdown counter (34) provides a predetermined countdown of the signal output by the day counter (32) and, at the end of the count, generates a Timeout signal. The predetermined countdown value is determined by a value stored in a register (36) which can be protected by a customer lock out circuit (42).
18 Citations
20 Claims
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1. A time base circuit provided with internal calibration, comprising:
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oscillator means for providing an output signal having a predetermined operating frequency; programmable counter means for receiving the output of said oscillator means and dividing said operating frequency by a factor of n to provide a reference signal operating at a reference frequency; storage means for receiving from an external source the value of n for storage thereof and for interface of the stored value of n with said programmable counter means; and inhibit means for inhibiting change of the value of n in said storage means after storage thereof; said reference frequency being a calibrated value and determined after measurement of said output signal from said oscillator means, such that said programmable counter means provides an internal calibration capability. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A timeout timer with internal calibration, comprising:
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an internal battery for providing an internal battery voltage; oscillator means for providing an output signal having a predetermined operating frequency, said oscillator powered by said internal battery voltage, said operating frequency being dependent upon the voltage level of said internal battery voltage; programmable counter means for receiving the output of said oscillator means and dividing said operating frequency by a factor of n to provide an output reference signal at a reference frequency; programming means for programming said programmable counter means and receiving the value of n from an external source and storing the value of n therein; first inhibit means for inhibiting change in the value of n stored in said programming means; presettable countdown counter means for receiving a predetermined count value, said presettable counter means operable to receive the output of said programmable counter means and count the cycles of said reference frequency by said predetermined count value and outputting a timeout signal at the end of said count; register means for receiving and storing from an external source said predetermined count value to interface with said presettable countdown counter means; and second inhibit means for inhibiting alteration of said predetermined count value stored in said register means. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
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16. A method for providing a time base with internal calibration, comprising the steps of:
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generating signal having a predetermined operating frequency; storing a value of n received from an external source; inhibiting alteration of the value of n after storage thereof; dividing the operating frequency by the value of n to generate a reference signal having a reference frequency; generating an internal battery voltage wherein the operating frequency varies as a function of voltage, the internally generated battery voltage enabling a virtually constant operating frequency; and maintaining storage of the value of n as a function of the uninterrupted presence of said internal battery voltage. - View Dependent Claims (17, 18, 19, 20)
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Specification