mattew zac wrote:
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you mean that I have to set the port pin at the beginning of my code? so if the switch is open the pin will remain high and if is closed, the pin will be connected to GND and will be low?
is that right?

Correct!

I don't know if Erik has already pointed you to them, but read the 3 80C51_FAM_*.pdf documents they are at:
http://www.semiconductors.philips.com/products/...other.html

Best regards,
Rob.