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RESET Circuit for Microprocessors

IP.com Disclosure Number: IPCOM000060449D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Herring, LC: AUTHOR [+3]

Abstract

In a typical microprocessor system, a circuit is required to reset the microprocessor when power is first applied. In addition, in many systems, a circuit is required that will hold the microprocessor in a reset state as power is going down, or is "dipping," to prevent damage to the circuitry from random processor sequences caused by low processor supply voltage. The circuit in the figure accomplishes this task. The input voltage is at a level higher than required by the microprocessor. This voltage is reduced by the voltage regulator VR1 to voltage V2 which supplies the voltage to the microprocessor. The voltage V1 is fed to a voltage reference circuit composed of R1 and ZD1. ZD1 is a zener diode that has a constant voltage drop across it. The resistor R1 is calculated to provide some minimum current through ZD1.

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RESET Circuit for Microprocessors

In a typical microprocessor system, a circuit is required to reset the microprocessor when power is first applied. In addition, in many systems, a circuit is required that will hold the microprocessor in a reset state as power is going down, or is "dipping," to prevent damage to the circuitry from random processor sequences caused by low processor supply voltage. The circuit in the figure accomplishes this task. The input voltage is at a level higher than required by the microprocessor. This voltage is reduced by the voltage regulator VR1 to voltage V2 which supplies the voltage to the microprocessor. The voltage V1 is fed to a voltage reference circuit composed of R1 and ZD1. ZD1 is a zener diode that has a constant voltage drop across it. The resistor R1 is calculated to provide some minimum current through ZD1. This network produces a reference voltage V3 that is applied to the positive input of voltage comparator M1 through resistor R4. The voltage V1 is also applied to the voltage divider network composed of resistors R2 and R3. The output of this circuit is applied to the negative input of M1. The resistors R4 and R5 provide hysteresis to the circuit to aid in stability. The resistor R6 is provided to pull up the output of M1 to the correct processor levels. The circuit operation can be described in three states based on the level of V1. 1. When V1 is less than (V2+2) volts, the output of VR1 is approximately 2 volts less than...