Method and circuit for performing automatic power on reset of an integrated circuit
AssigneeFairchild Semiconductor Corporation
InventorHassan Hanjani
Life of this patent
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Abstract
Method and circuitry for automatic resetting of an integrated circuit upon power up handles multiple clock sources and minimizes power dissipation. A robust voltage sensing circuit detects power up and triggers resetting of most of the circuit with the exception of the initialization circuit that includes an internal oscillator. After the circuit determines that the internal oscillator signal has settled, contents of non-volatile register are read to select the clock source for the circuit. Upon successful selection and clean up of system clock, the reset is removed.
Claims18
A method for resetting an integrated circuit upon power up, the method comprising:
- detecting a voltage level on a power supply node and generating a power on detect signal when the voltage level reaches a predetermined level;
- asserting a reset signal in response to the power on detect signal, the reset signal disabling a plurality of internal circuitry except at least an internal oscillator;
- counting a first predetermined number of cycles of an oscillating output of the internal oscillator;
- and
- reading contents of a first register to select a clock source after the completion of the counting step.
An integrated circuit comprising:
- a controller;
- a clock circuit coupled to the controller and configured to select between a plurality of clock sources including an internal oscillator;
- a voltage sensing circuit configured to detect a voltage level on a power supply node;
- a global reset circuit coupled to the voltage sensing circuit and configured to generate a global reset signal that, when activated, resets most of the integrated circuit except for at least the internal oscillator;
- and
- a register coupled to the clock circuit, and configured to store clock information,
- wherein, when the voltage sensing circuit detects a power up condition, the internal oscillator automatically runs for a predetermined number of cycles before the contents of the register are read to select one of the plurality of clock sources.
Dependencies are inferred from the claim text.