a program w/ pin addresses using parallel port?

i used 3 seven segments , 2 are conected in data register and 1 in control register.

a cashier w/ output only 1&2. and each cashier has it's own counter from 0-99. and 2 push button connected in status register.each push button determines the cashier. each time a push button is pressed it will determine the cashier and it's counter. also the program needs to check every 5 sec. if any of the push button has been pressed. on the other hand this is a parallel port interfacing.