I am pretty new to the circuit and I am trying to design a 4 (decimal 3,2,1,0) to 3 (base2 00, 01, 10, 11) encoder. I know how the internal, but I have no idea to represent those constant in Logisim, and I dont want user to choose more than one input.

Help appreciated!

 

try two OR gates

each has two connections

one to input "1" and "3" the other to input "2" and "3".

(input zero would not be used in this configuration - ala idiot switch)

 

Look at Page 5 of a BCD to Binary Converter

That gives a truth table for what you are trying to accomplish, but goes into double digit decimal numbers to binary.