Discussion in "Project Help" started by    chhabiraj    Feb 4, 2009.
Wed Feb 04 2009, 04:52 AM
I am making project XY recorder using Micro controllerAT89C52.

This my first project .

I don`t know how to decide the value of resistor and capacitor at RESET Pin.

so help me Please.
Wed Feb 04 2009, 02:37 PM

resistor: 8K2, 1/4 watt (8.2K)
capacitor: 10uF,16V

hope you know how the above components are connected to the reset pin.

Wed Feb 04 2009, 03:13 PM
in case if u dont knw plz refer to the image below.....

the LED is optional....

Tags 8051 reset circuit8051 tutorials8051 projects
Tue Feb 10 2009, 12:16 PM
thanx... for your help.

My controller chip is to run at +5 V ..

so that capacitor charging time should be less than the time required by the controller to scan the reset Pin..

Depending on that basic How can I determine the value of resistor and capacitor?
Tue Feb 10 2009, 12:50 PM
sir, as far as i know the values are fixed for all applications..... like they are standard values..... their values donot differ from application to application
Tue Feb 10 2009, 07:40 PM
10uF and 8.2K is generally used, but logic behind this selection is as follows..

Whenpoweris turned on, the circuitholdsthe RSTpin highfor an amountof time that dependson the capacitor valueand the rate at whichit charges.To ensurea valid reset the RSTpin must be held high longenough to allow the oscillator to stsrt up plus two machine cycles.

On power up, VCCshould rise within approximately ten milliseconds.The oscillator start-up time will dependon the oscillatorfrequency.Fora 10MHzcrystal, the start-up timeis typically1rns.For a 1MHzcrystal, the start-up time is typically 10ms.

Inter 8051 Manual

Hope this answered your query I suggest any new student to read Intel Manual for learning 8051.

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