hi guys
i am having certain issues connecting the decoder and the seven segment display.rest of the circuit is sorted out but could not figure it out how to use the 3,4,5, legs of the decoder
all the legs are active low inputs
plz reply as soon as possible

 

Links are busted.

Pin 3 - Lamp Test will turn all of the segments on ("active"). The diplay will look like the number "8".
Pin 4 - RBO - Ripple Blanking Output
Pin 5 - RBI - Ripple Blanking Input

Ripple blanking is the process of supressing the display of leading zeros in a multi-digit display. The truth table on page 3 of the TI data sheet has the details.

http://focus.ti.com/lit/ds/symlink/sn7447a.pdf

Consider a three digit display. If the value to display is "56" you can display a blank followed by the digits "5" and "6" or you can display "056". It is all up to you how you want your display to look.