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Joined Jan 1, 2008
Hello Can Anybody Suggest Me To Rectify The Fault Of 89c51 Microcontroller . Actually I Designed A Circuit Of Latch And Some Trigger Circuit Which Is Trigeered By A Microcontroller 89c51the Problem Was When I Switch On Supply Momenyerely All The Port O/ps Of Mc Goes High Which Triggers All Latch And Other Circuits .


Joined Feb 24, 2006
This is not a fault in the processor, it is the fault of the designer who did not take RESET behavior into account. At RESET all pins should go to a defined state. A very convenient initial state is to be a high-impedance input. The quasi-bidirectional port of the original 8051 architecture (circa 1978) also makes this a very weak output high.

The well known solution for this problem is to make your outputs operate active low or to have an external lockout that prevents them from being turned on before the processor acquires control. If you insist on using active high outputs then you can require a greater current than the processors output pin can provide to turn them on. The solutions to your problem are numerous, but first you have to understand the output structure of the part you are using.