How to multiplex 4x7segments with switches by using timer interrupt.

I am using AT89c2051 to multiplex 4x7 segments by configuring P3 as buffer for segments and P1.0~P1.3 as control bits for segments,two switches also connected at P3.0 and P3.1, I used the timer interrupt for multiplexing but i failed to use switches because thats are connected at same port which is being used for buffer for segments.Can anyone tell me how to use switches when using timer interrupt.