Why my AT89s5x sometimes needs to reset power supply ?

help about AT89s5x

hello
sometimes when i connecting the power suply to my chip it doasent work properly and then when i try again it work properly. does anybody know why somtimes my circuit need to reser supply?
i write my programs bye assembly language and i use adapter with 500mA current as power suply . and i use 7805 for regulat and my reset circut is one resistance and one capacitore, those are 10µf and 8.2KΩ
i use 12MHZ crystall and two 33PF for oscillator
thank you for your help

Re: help about AT89s5x

Hi Navid,

Read carefully the three application notes from Atmel site. These are a good starting point to solve your problems generated at start-up.

Analyzing the Behavior of an Oscillator and Ensuring Good Start-up (16 pages, updated 07/04)
This application note explains how an oscillator functions and which methods can be used to check if the oscillation conditions are met in order to ensure a good start-up when power is applied

http://www.atmel.com/dyn/resources/prod_documents/doc4363.pdf

External Brown-out Protection for C51 Microcontrollers with Active High Reset Input (15 pages, updated 11/02)
This Application Note shows in detail how to prevent system malfunction during periods of insufficient power supply voltage.

http://www.atmel.com/dyn/resources/prod_documents/doc4183.pdf

How to Calculate the Capacitor of the Reset Input of a C51 Microcontroller (8 pages, updated 10/03)
This Application Note explains how the reset of the 80C51 microcontroller works when the RST pin is a pure input pin and when the RST input is bi-directional. It gives rules to determine the extra components required to operate the reset function properly

http://www.atmel.com/dyn/resources/prod_documents/doc4284.pdf
http://www.atmel.com/dyn/resources/prod_documents/Reset-V13.xls

Regards,
silvio

help about AT89s5x

Maybe u can check your oscillator, ensure the length of the trace keep the same, and it should near the PIN of MCU.

Re: help about AT89s5x

What is your application? I mean, what does your microcontroller do? Does it drive DC motors? Does your circuit have relays? Does it need high current? Make sure your power supply can deliver enough current.

Noise on Vcc and ground tracks do exist, causing the micro to sometimes get 'hang'. To minimize them, give enough power supply current, make larger track widths, separate high current ground tracks from the ground tracks for digital circuitry part.

Try putting a decoupling capacitor (100nF) near the Vcc pin of every digital IC's, including your microcontroller. Check your PCB for bad soldering. From my experience, when you are very sure that your program is OK, the problem usually comes from hardware.

Re: help about AT89s5x

hello
my problem has been solved , i usually connect my micro after regulator but i connect other devices before regulator so a lotof current used by other divices.
(-;
thank you

Re: help about AT89s5x

One good advice is not to relay on single-capacitor reset circuit.
If you always use proper IC, such as DS1323, LM809M3, .. many others .. you will never have problems with properly reseting microcontroller and associated circuits ..