Low cost/low current watchdog circuit for microprocessor
First Claim
1. A low current watchdog circuit for monitoring a microprocessor status signal and producing a reset signal, said watchdog circuit comprising:
- an input for receiving the status signal output from a microprocessor;
an energy storage device adapted to receive energy from an energy supply;
a sensor for sensing an amount of energy associated with the energy storage device and comparing the sensed amount of energy associated with the energy storage device with a threshold amount and producing a reset signal in response to the comparison, the sensor controlling the rate of energy flow into the energy storage device; and
an output adapted to provide the reset signal to the microprocessor;
wherein the sensor includes a voltage detector for monitoring a voltage potential across a voltage charging capacitor associated with the energy storage device, the voltage detector operating as a current sink to draw a small current that charges the capacitor, thus providing a watchdog circuit exhibiting a low quiescent current.
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Accused Products
Abstract
A watchdog circuit and method are provided for monitoring a microprocessor to detect the presence of a malfunction condition such as a program lock-up. The watchdog circuit includes a first capacitor coupled to a supply voltage and a transistor having a collector and emitter coupled in parallel with the first capacitor. The transistor has a base for receiving a signal in response to a status output signal generated by the microprocessor. A voltage threshold detector is provided for comparing a voltage potential associated with the capacitor with a predetermined threshold voltage and producing a reset signal in response thereto. The threshold voltage detector produces a small current which is utilized to charge the first capacitor. The reset signal is provided to the microprocessor to initiate a reset operation which will reset the microprocessor in an attempt to eliminate the malfunction condition. Additionally, a feedback path may be provided between the output and the base of the transistor to allow for repetitive reset signals during a continuous microprocessor malfunction condition.
75 Citations
15 Claims
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1. A low current watchdog circuit for monitoring a microprocessor status signal and producing a reset signal, said watchdog circuit comprising:
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an input for receiving the status signal output from a microprocessor; an energy storage device adapted to receive energy from an energy supply; a sensor for sensing an amount of energy associated with the energy storage device and comparing the sensed amount of energy associated with the energy storage device with a threshold amount and producing a reset signal in response to the comparison, the sensor controlling the rate of energy flow into the energy storage device; and an output adapted to provide the reset signal to the microprocessor; wherein the sensor includes a voltage detector for monitoring a voltage potential across a voltage charging capacitor associated with the energy storage device, the voltage detector operating as a current sink to draw a small current that charges the capacitor, thus providing a watchdog circuit exhibiting a low quiescent current. - View Dependent Claims (2, 3)
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4. A low current watchdog circuit for monitoring a microprocessor status signal, comprising:
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input means for receiving a status signal output from a microprocessor; a first capacitor coupled to a supply voltage; a transistor having a collector and emitter connected in parallel with said first capacitor, said transistor further having a base for receiving a signal in response to said status signal; a voltage threshold detector for comparing a voltage potential associated with said first capacitor with a predetermined threshold voltage and producing a reset signal in response to detecting a microprocessor malfunction condition, said threshold voltage detector operating as a current sink to draw a small current that charges said first capacitor, thus providing a watchdog circuit exhibiting a low quiescent current; and output means adapted to be coupled to a reset input of said microprocessor for providing said reset signal to the microprocessor. - View Dependent Claims (5, 6, 7)
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8. A low current watchdog circuit for monitoring a microprocessor status signal and producing a reset signal in response to detecting a malfunction condition, said circuit comprising:
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input means for receiving a status signal output from a microprocessor; a first capacitor having a first terminal coupled to a supply voltage; a transistor having a collector and emitter connected in parallel with said first capacitor, said transistor further having a base for receiving a signal in response to said status signal; a voltage threshold detector integrated circuit coupled to a second terminal of said first capacitor for comparing a voltage potential associated with said first capacitor with a predetermined threshold voltage, said detector circuit producing a reset signal in response to detection of a microprocessor malfunction condition, and said threshold voltage detector operating as a current sink to draw a small current that charges said first capacitor, thus providing a watchdog circuit exhibiting a low quiescent current; and output means adapted to be coupled to a reset input of said microprocessor for providing a reset signal to the microprocessor. - View Dependent Claims (9, 10, 11)
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12. A method for monitoring a microprocessor status signal and providing a reset signal to a microprocessor in response to detection of a malfunction condition, said method comprising:
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receiving a status signal output from a microprocessor; charging a capacitor with a small current drawn by a threshold voltage detector to achieve a voltage potential, the threshold voltage detector operating as a current sink to charge the capacitor, thus providing a monitoring method exhibiting a low quiescent current; discharging the capacitor with a transistor controlled in response to the status signal; comparing a voltage potential at one terminal of the capacitor with a predetermined voltage potential provided by said threshold voltage detector; and generating a reset signal in response to said step of comparing and providing said reset signal to a microprocessor to reset the microprocessor upon detecting a malfunction condition. - View Dependent Claims (13, 14, 15)
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Specification