why in micro controller 8051 pull up resistors are not connected internally at port 0

[uday mehta]

all remaining three ports have pull up resistors internally. then why port 0 has not inter pull up resistors?

 

[tpetar]

all remaining three ports have pull up resistors internally. then why port 0 has not inter pull up resistors?

You just forget to mention what uC, you mention 8051 and this is family of microcontrollers.

 

[FvM]

Port 0 has dynamical push-pull instead. Omitting weak pull-ups apparently seemed appropriate to the original 8051 designers. The detail has been copied with each 8051 compatible IO-port since 30 years. 8051 developers use to know this, or learn it later on.