Hi all,
I am working on a project based on AT89C55. Here if i connect pull up resistor's of 10K to port '0',then it gives problem i.e. my controller get stuck up without giving any display on LCD. If i disconnect pull up, it works properly, giving always low on port 0 pins.[even i write FF to port 0 through program ].
I have tried with 1K pull up also,but nothing improvement. Also i need high-low transition on Port 0. I hv not connected any pull up to Port 1,2,3 as it has internal pull ups.


Plz.......... suggest.

 

Sir,
Thanks for the quick reply.

Yes i am using port 0 as output pin. Also i have connected 74LS244 to this port pins directly & after that optocoupler . Here i want to switch on my output optocoupler by giving low to it.So initially all port pins should be at high, which i cant get.

Also i tried with another working microcontroller, but i didnt get any results.

Plz check out circuit diagram attached here n give your valuable suggestion.

I have not connected 0.1 microF cap at port pins,which are shown in digram.

Thnks n waiting for reply.

 

Sir,
I am using PC847 optocoupler.Thnks for the suggestion i'll think on it, But i m talking about microcontroller port 0 problem.Therer is 74LS244 IC between optocoupler & microcontroller,due to which this problem occur.

Plz .......suggest on this issue.

Thnks

 

Sir,
sorry for the delay in reply.
I tried with your suggestion but it didn't work .If i connect pull up of 10 k to all port 0 pins except pin no 32 then it works correctly. But if i connect pull up of 10 k to pin 32 then again my controller gets stuck up.Here there is no load on port pins,only pull up is there.

For this i have tried with another new controller but nothing happen.

Also i am facing new problem--- whenever i switch on power ,until i touch any of the port pin controller doesn't start executing program. It seems like any grounding
problem. Whether it is necessary to connect pull up to all port though they have internal pull ups?


thanks & please suggest on this.