8051 basic question IO ports

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Because i am new at 8051, i would like to know:

For example lets use port P1.
If i want to output something i just write P1 = number; in keil C.
As i understand that value will be always on that port until next write.

If it is true, and if i want now to receive something on P1, it can not be received if port is already transmitting something. How to prepare port for input?
 

for basic 8051 ,
if you want to make as input port
you must first write '1' to that port bit ,
then you can operate it as input port.

this is a must for 8051 before you apply any input voltage to port bit.

srizbf
15thmay2010
 

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    PCBwire

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Thanks, that was fast!
 

On power-on (or after reset) all P0-P3 pins have written a "1" into them, so they are already set as inputs .. see attached table ..

IanP
 

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    PCBwire

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It also depend upon which microcontroller ur using..
In some 8051 u have to decide direction of the port i.e. output or input
I f its bidirectional port then above logic is true i.e. writing 1 before reading..
 

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    PCBwire

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