The PC Keyboad has only a couple of signals to interface it. You can use one of the external Interrupt pins to get the microcontroller attention at keyboard time. There are also the input capture pins from timers that can be used to also generate interrupts to the CPU from an external signal.

There may actually be some 8051 derivatives that have a port that has status change interrupt hardware. I would look first at the Philips LPC932 to see if it has this feature.

Michael Karas

PS......For full explanation on the quasi bi-directional port operation of typical 8052 type chips hit the tutorial button at the left.

MJK