Years ago(4-5 yrs) I've tried to interface the PC Key board with Atmel's 89c52, threre were 4 wires, 2-data & 2-power for interface using PS-2 connector...I've also seen RTC & LCD for data entry and time setting display..I've nod done programming but...my senoirs were there n they did that...I was initial phase of programming at that time..u can search for the post here or also at
www.8052.com...u can get help from there ...also 89c51 / AVR controller's application notes also contains some info. for the same...
Raj