hi;
all port pins are better at sinking current than sourcing.i am afraid some of you had a look at IOH which is a current sourced by port not sunk by it.instead look at IOL.it is the current sunk.its value for non bus ports like P1 is 1.6 mA for Atmel 89c52.use
the diode with its anode connected to 5v via a resistor and cathode to port pin.when you wish to turn it on write 0 at that pin.
Pranav