i need to make a circuit that can convert 8bit number system.

we should be able to choose what base is your input, and give the value of your input using numeric keypad. then it will display the outputs in 7 segment common cathode for decimal, octal and hexadecimal and LED for binary.

pls help me what IC should b used.. and how to use that IC

 

The policy of this forum is that the Original Poster states his problem along with his attempt to solve it, even if it went wrong or didn't manage to finish it. You must make an effort yourself if you expect the community to make an effort to help you.

I will say however that there are IC's that convert binary to decimal numbers, like the 7447. From binary to decimal, you can do the same but by grouping the digits in triads and inserting them to the 7447 decoder. The same with groups of 4 for the Hexadecimal.

This approach takes the binary system as the carrier of information and converts it to the other types. If you want however to input the number in decimal form you will have to find keypads or something and I don't know how to manage that.