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Microprocessor Monitor and Reset Circuit

IP.com Disclosure Number: IPCOM000061224D
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Balliet, L: AUTHOR [+2]

Abstract

This article describes a circuit arrangement which has means of providing a reset signal to a microprocessor for power up or when the microprocessor is not executing code correctly. The need for this circuit appeared in applications of microprocessors in modules which required an automatic reset (manual reset not available) when the micro improperly executed code. An example is a micro-based module in an automobile which cannot be reset by the operator. The drawing illustrates the present circuit arrangement. Software (microcode), when properly executed, causes port P4 to toggle. Capacitor C5 and pull-up resistor R13 assure that only a negative-going signal at Pin 5 of inverter U2C causes Pin 6 of the U2C to charge C6 through diode CR4. CR4 prevents C6 from discharging through U2C.

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Microprocessor Monitor and Reset Circuit

This article describes a circuit arrangement which has means of providing a reset signal to a microprocessor for power up or when the microprocessor is not executing code correctly. The need for this circuit appeared in applications of microprocessors in modules which required an automatic reset (manual reset not available) when the micro improperly executed code. An example is a micro- based module in an automobile which cannot be reset by the operator. The drawing illustrates the present circuit arrangement. Software (microcode), when properly executed, causes port P4 to toggle. Capacitor C5 and pull-up resistor R13 assure that only a negative-going signal at Pin 5 of inverter U2C causes Pin 6 of the U2C to charge C6 through diode CR4. CR4 prevents C6 from discharging through U2C. U2D, C6 and R14 form an astable multivibrator whose output at Pin 8 remains low as long as C6 is charged through CR4 faster than it is discharged through R14. If P4 ceases to toggle, C6 discharges and U2D switches state causing Pin 8 to go high (micro is reset). With reset high, C6 charges through R14 until U2D switches state, causing Reset to go low allowing micro to run. CR3 provides power-up reset by discharging C6 when +5V supply turns off. Discharge path is through positive supply when it is low. When power (+5 V) is restored, the reset pin 8 of U2D goes high until C6 is recharged through R14. The key to the circuit is the use of Schmidt t...